Materials with a 1^st order magnetic transition have attracted much attention because of their large magnetocaloric effect, i.e. a large isothermal entropy change (ΔS) induced by a pseudo-static magnetic field. While this material family has hitherto almost solely been studied for the magnetic cooling effects due to the reversibility of ΔS, we have found that the irreversible heating power (i.e. energy loss) could be enhanced dramatically near T_C due to the magnetic phase coexistence associated with the 1^st order magnetic transition. An example of such a unique effect was observed in LaFe_11.57Si_1.43H_1.75 with its upper T_C of 319 K. The spontaneous magnetization (M_s) shows a very abrupt decrease from 110 Am²/kg at 316 K to zero at 319 K. This large M_s immediately below T_C along with the enhanced irreversibility of the hysteresis curve result in a specific absorption rate as large as 0.5 kW/g under a field of 8.8 kA/m at 279 kHz. This value is nearly an order of magnitude larger than that observed under the same condition for conventional iron oxide-based materials. Moreover, the large heating effect is self-regulated at the 1^st order T_C (319 K) which resides in the ideal temperature range for hyperthermia treatment of cancerous cells. This proof-of-concept study shows that the extraordinary heating effect near the 1^st order Curie point opens up a novel alloy design strategy for large, self-regulated induction heating.

We have shown that theranostic properties of the magnetic nanostructures (MNS) can be significantly enhanced by tuning their core composition and length of surface coating. In this study, we have synthesized monodisperse metal ferrite (MFe₂O₄) nanoparticles of size 8 nm using thermal decomposition method and functionalized with nitrodopamine conjugated polyethylene glycol (NDOPA-PEG). The composition was controlled by tuning the stoichiometry of MFe₂O₄ nanoparticles (where M = Fe, Mn, Zn, Zn_xMn_1-x) while the length of surface coating was tuned by changing the molecular weight of PEG (200 to 2000). The PEGylated MFe₂O₄ nanoparticles demonstrated high colloidal stability across a wide pH range (6-10) and cell culture medium and the cell viability studies showed no cytotoxicity. After optimization, the r₂ relaxivity of 552 mM^-1s^-1 and specific absorption rate of 355 W/g was obtained. Our results suggest that both core as well as surface coating are important factors to take into consideration during the design of theranostic MNS. When coupled with the desired targeting agents, these ultra-stable MNS have great potential in targeted theranostic applications.

Magnetic nanoparticles could help to improve clinical practice in the treatment of cancer, most probably in synergy with other conventional treatments [1]. There already exist methods to obtain magnetic nanoparticles with the appropriate properties to be used in diagnosis and therapy but these properties need to be optimized to avoid its alteration after intravenous injection due to aggregation in lysosomes inside cells or accumulation in tissues [2, 3].
In this work we will show the effect of different characteristics of the magnetic colloids, such as particle size and size distribution, colloidal properties of the aqueous suspensions, such as hydrodynamic size and surface modification, and magnetic properties that depend on the synthesis route, on their MRI relaxivity and heating capacity. Magnetic nanoparticles biodistribution and its transformation over time are also affected by these parameters and can be tracked by AC magnetic susceptibility measurements. This technique allows identifying and quantifying magnetic nanoparticles in tissues, differentiating them from other endogenous species such as the ferritin iron cores [4].
References
[1] M. Colombo, et al, Chem. Soc. Rev., 41, 4306, 2012.
[2] Y. Luengo, et al, Nanoscale, 5, 11428, 2013; A. Ruiz, et al, Nanoscale, 5, 11400, 2013.
[3] L. Gutiérrez, et al, Dalton Transactions 2015 (in press).
[4] R. Mejías, et al, Journal of Controlled Release 171, 225, 2013; L. Gutiérrez, et al, Phys. Chem. Chem. Phys., 16, 4456-4464, 2014;
Acknowledgements
This work was partially supported by projects from the Spanish Ministry of Economy and Competitiveness (MAT2011-23641), EU-FP7 MULTIFUN project (246479), EU-FP7 NANOMAG (604448), and AXA Research Fund (L.G.).

The side-effects of non-steroid anti-inflammatory drugs used in the management of osteoarthritis have elicited considerable research interest in the alternative treatment modalities including hyperthermia treatment of degenerated knee joint. This treatment may be extended to orthopaedic applications for economic and ergonomic purposes. Here, we report the use of Polyvinylidene fluoride (PVDF) encapsulated Chromium doped Iron (III) Oxide (CFO) nanocomposite for hyperthermia treatment of osteoarthritic knee joint. CFO was synthesised by sol-gel processing route and encapsulated in PVDF matrix using acetic acid media. X-Ray Diffraction (XRD) and Rietveld analysis confirmed the formation of CFO. Room temperature Vibrating Sample Magnetometry (VSM) and Differential Thermogravimetric Analysis - Differential Scanning Calorimetry (DTA-DSC) were used to analyse the magnetic and thermal properties of the encapsulated composites respectively. Scanning Electron Microscopy (SEM) was used to study the morphology of the composites. MTT assay confirmed the non-toxic nature of the nanocomposite. 3D finite element method (FEM) simulation of toroid and spherical geometry of the PVDF-CFO was carried out and the effects of volume percentage, geometry, implantable positions were studied using this method. The implications of the results for the development of implantable devices for the localized treatment of osteoarthritis have also been discussed.

Abstract: In the current study, an in vitro blood-brain barrier (BBB) model was developed using a triple co-culture of immortalized murine brain endothelial cells, immortalized murine astrocytes and mouse brain vascular pericytes. By measuring the permeability coefficients and TEER values [1], we examined the tightness of the cell monolayer and confirmed that this method has enabled brain endothelial cells to cross-talk with neighboring cells and therefore improved the integrity of the in vitro BBB model. After the model was successfully established and confirmed, permeability of several nanoliposomes was determined using this model.
Materials and Methods: The collagen coated nanoliposome and PEG coated nanoliposome were prepared and encapsulate with iron oxide [2]. SEM was used to characterize their surface morphology and TEM was used to assess the iron oxide inner core diameter. For the in vitro blood- brain barrier model, pericytes were cultured and seeded on the bottom side of the collagen-coated Transwell® inserts and astrocytes were seeded on the bottom of the 24-well plates separately. After 12 hours of adhesion, murine brain endothelial cells were seeded onto the upper side of the inserts and the inserts would then be placed in the 24-well plates containing astrocytes. The model would be evaluated and confirmed using TEER and FITC-Dextran transport [3]. Then, the model was used to test the permeability of the various nanoparticles. The model would be exposed to nanoparticles for 2 hours. After 2 hours, an iron assay kit was used to determine the iron concentration that passed through the model. Each experiment was conducted in triplicate and repeated at least three times.
Results and Discussion: Previous results showed that the highest permeability was obtained from collagen coated nanoparticles. This result suggests that nanoliposomes coated with collagen had better permeability across the BBB than nanoliposomes coated with PEG.
Conclusions: Through such experiments, magnetic nanomaterials (such as magnetic nanoliposome) suitable for MRI use which are less permeable to the blood brain barrier to avoid neural tissue toxicity and magnetic nanoliposomes suitable for brain drug delivery since they were more permeable to the BBB were created.
References: [1] Pardridge WM. Molecular Trojan horses for BBB drug delivery. Curr Opin Pharmacol. 2006; 6:494-500. [2] Krishnamoorthy G, et al. Collagen Coated Nanoliposome as a Targeted and Controlled Drug Delivery System. AIP Conf. Proc, 2010; 1276, 163. [3] Bennett J, et al. Blood-brain barrier disruption and enhanced vascular permeability in the multiple sclerosis model EAE. J Neuroimmunol. 2010; 229:180-191.

The properties of magnetic nanoparticles vary dramatically with size, and reproducibly controlling size is critical for practical applications. This is particularly true when moving into clinical settings, where regulatory approval requires demonstrated reproducibility in efficacy that can only be achieved with excellent size control. We present a general method for size control in the synthesis of nanoparticles by establishing steady state growth through the continuous, controlled addition of precursor. The steady state growth regime is characterized by a constant concentration of unreacted precursor as well as a uniform rate of growth in particle volume. This approach, which we have termed the “Extended LaMer Mechanism” of growth allows reproducibility in particle size from batch to batch, as well as prediction of size produced later in a reaction by monitoring early stages of growth. We have demonstrated this method using an important and challenging synthetic system, magnetite nanoparticles. To facilitate this reaction, we also devised a reproducible method for synthesizing an iron oleate precursor that can be used without purification. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000

Magnetic nanoparticles are unique among nanomaterials due to our ability to control their translation and rotation, and actuate thermal release, through the application of magnetic field gradients and time-varying magnetic fields. Furthermore, because of their biocompability and the fact that magnetic fields penetrate through the body, magnetic nanoparticles possess tremendous potential for biomedical applications. In this talk I will discuss our recent work aimed at understanding the response of magnetic nanoparticles to time-varying magnetic fields and engineering of magnetic nanoparticles for biomedical applications, such as thermal cancer therapy, magnetic particle imaging, and probing the mechanical properties of biological environments.

While magnetic nanomaterials have already been used in clinics for contrast enhancement in magnetic resonance imaging (MRI) [1], there has been no clinical approval for a drug delivery system containing such nanoparticles, yet. Magnetic nanoparticles currently investigated for their possible application in biomedicine are predominantly different crystalline polymorphs of iron oxides. For small enough crystal sizes, iron oxides exhibit the so-called “superparamagnetic” behavior, a feature combining high magnetization with very low coercive forces. Such superparamagnetic nanoparticles show great potential in therapeutic applications due to their ability to transform the energy of an alternating magnetic field to thermal energy in what is often called magnetic fluid hyperthermia [2]. These particles dissipate thermal energy by magnetic relaxation through the Brownian and Neel mechanisms. Therefore, aqueous suspensions at relatively higher nanoparticle concentrations (g/L), the so-called “ferrofluids”, also increase their temperature in the presence of an alternating magnetic field [3]. In this work, a composite multi-scale structure consisting of the biopolymer alginate, functional nanoparticles and a model drug is fabricated and analyzed. We examine the potential of flame-made SiO₂-coated Fe₂O₃ nanoparticles [4] as the stimuli-responsive material in the multi-scale composite structure. We perform detailed physicochemical and magnetic characterization on the hybrid alginate hydrogel beads and evaluate their potential in magnetic fluid hyperthermia and enhanced biomolecule release in the presence of an external AMF. The possibility to externally stimulate drug release will open up new possibilities in intelligent, on-demand drug administration.
References
[1] A. Singh, S. K. Sahoo, Drug Discov. Today, 19, 474-481 (2014).
[2] A. Jordan, R. Scholz, P. Wust, H. Fahling, R. Felix, J. Magn. Magn. Mater., 201, 413-419 (1999).
[3] G. A. Sotiriou, M. A. Visbal-Onufrak, A. Teleki, E. J. Juan, A. M. Hirt, S. E. Pratsinis, C. Rinaldi, Chem. Mater., 25, 4603-4612 (2013).
[4] A. Teleki, M. Suter, P. R. Kidambi, O. Ergeneman, F. Krumeich, B. J. Nelson, S. E. Pratsinis, Chem. Mater., 21, 2094-2100 (2009)

An intricate spatial and temporal control of magnetic microbeads during their motion is important for the successful transport of labelled chemical and biological species in microfluidic cells. Especially monodisperse beads with a superparamagnetic particle-loaded shell and a diameter of a few micrometers act as a model system for biological cell manipulation.
We present a detailed study, comprising bead entrapment and its phase-delayed continuous motion by periodic rotation of external magnetic fields, a frequency modulated local displacement, and thus a reduced bead velocity. The experimental data is underlined by a numerical model of microparticle dynamics. An almost complete agreement between experiment and modelling on the motion dynamics, including the temporary excursion, of the beads is achieved.
Circular magnetic thin film structures are obtained by sputter deposition and subsequent optical lithography. Magnetic polystyrene particles of different sizes and magnetic content are employed to the magnetic platform. Rotating magnetic fields are applied in a magneto-optical microscope allowing for the corresponding observation of the magnetic domain structure. All experimental events, including bead settlement, movement, and escape from the magnetic disk are recorded in real-time. Micromagnetic simulations are used to calculate the magnetization vector distribution and the magnetic stray field distribution. The rotating gradient of energy potential is derived by integrating the stray fields over the bead volume, taking into account the individual volume susceptibility and diameter of the bead. The numerical approach is based on a mechanical harmonic oscillator model of microparticle motion. Comparing modeling and experimental results, the role of superparamagnetic susceptibility, external magnetic field strength, and particle mass for the maximum particle velocity is investigated. The validity of the modelling results is confirmed by direct comparison to experimental time domain data on circular magnetic structures. By applying different magnetic field amplitudes and rotational frequencies we are able to control and adjust the number of bead jumps. The experimentally observed regimes of microparticle motion on the structures are fully replicated by modeling.
The experimental and theoretically analyzed bead response provides guidance for the design of future and more complicated devices with different sizes and shapes of magnetic structure patterns, as the approach can be applied without loss of generality to arbitrary ferromagnetic structures. The results form the basis for advanced platforms like microparticle logic devices and lab-on-a-chip biological applications.
Support through the DFG (MC9/13-1) and their Heisenberg Programme (MC9/9-2) is acknowledged.
[1] E. Rapoport, G.S.D. Beach, Physi. Rev. B 87, 174426 (2013)
[2] A. Chen, R. Sooryakumar, Scientific Reports 3, 3124 (2013)
[3] B. Lim, V. Reddy, X.H. Hu, et al., Nat. Comm. 5, 3846 (2014)

Abundance and relatively low cost of Ce provide a great incentive for its use in rare-earth permanent magnets. Unfortunately, ferromagnetic compounds with Ce tend to have low values of the ordering temperature and saturation magnetization. It has been reported [1] that the tetragonal Ce(Fe,Co,Ti)₁₂ compounds may exhibit application-worthy intrinsic magnetic properties. In this work, an attempt has been made to convert these intrinsic properties into the functional properties of a permanent magnet. A series of Ce_1-xSm_xFe₉Co₂Ti alloys was synthesized via mechanochemical processing of a mixture of CeO₂, Sm₂O₃, Fe₂O₃, Co and TiO₂ powders with metallic Ca in the presence of a dispersant powder. Submicron anisotropic powders with the desired crystal structure were collected after washing off the CaO dispersant and reaction byproducts. Contrary to the report [1], the magnetic anisotropy field of CeFe₉Co₂Ti was found to be smaller than 20 kOe and insufficient for supporting a significant coercive field. At the same time, the Ce_0.5Sm_0.5Fe₉Co₂Ti powder exhibited a notable coercivity of 1.8 kOe and a remanence of 86 emu/g. The powder of the well-known SmFe₉Co₂Ti compound, which was synthesized mechanochemically for the first time, exhibited a coercivity of 5.8 kOe. More detailed structural, microstructural and magnetic data will be presented and discussed.
[1] D. Goll, R. Loeffler, R. Stein, U. Pflanz, S. Goeb, R. Karimi,G. Schneider, Phys. Status Solidi RRL 8, 862 (2014)

Since Skomski et al. predicted a giant energy product of around 1 MJ/m³ for a composite material of Sm₂Fe₁₇N₃/Fe₆₅Co₃₅ (1)._, spring magnets are considered as promising candidates for the next generation of high performances permanent magnets (2). Composed of a mixture of hard and soft phases, spring magnets benefit from an effective exchange coupling (3). Theoretical studies showed that small soft grains of a few nanometers are required (1,3). The chemical routes of magnetic nanoparticles with controlled size and shape are now well mastered, opening wide potentiality for bottom-up approaches of new effective spring magnets (4,5).
We attempted to produce two kinds of exchange coupled magnets, by mixing and annealing fcc FePt NPs with FeCo NPs, and L1₀ FePt NPs with Co nanorods (NRs). The 6 nm fcc FePt NPs were synthesized by the reduction of metallic salts adapted from ref. (6), while the L1₀ FePt NPs were obtained following a multi-step process adapted from ref. (7). 5-8 nm FeCo NPs were obtained by an organometallic synthesis developed recently at the LPCNO, and the Co NRs (diameter 10 nm, length 100 nm) were synthesized by the polyol process (8). The nanostructured materials were characterized by TEM, XRD, EDS, TGA and VSM. Our work was mainly focused on the characterization of the inter-phases exchange coupling by various magnetic analyses : M(H) loops at different temperatures, Henkel plots and recoil curves. In the annealed L1₀ FePt NPs/Co NRs system with 30% at. Co, the exchange coupling was evidenced by a single step hysteresis loop with a coercivity of 15 kOe at room temperature and by the study of the recoil curves. For the annealed fcc FePt NPs/FeCo NPs system with only 10% at. FeCo, the exchange coupling was evidenced by a single step hysteresis loop with a coercivity of 10 kOe at room temperature and a positive δM value. The comparison of the different magnetic analyses led to open questions on their reliability, depending on the system studied and on the volume fraction of the softer phase.
1. R. Skomski, J. M. D. Coey, Phys. Rev. B. 48, 15812 (1993).
2. N. Poudyal, J. Ping Liu, J. Phys. Appl. Phys.46, 043001 (2013).
3. E. F. Kneller, R. Hawig, Magn. IEEE Trans. On. 27, 3588-3560 (1991).
4. H. Zeng et al.,Nature. 420, 395-398 (2002).
5. F. Liu, Y. Hou, S. Gao, Chem Soc Rev. 43, 8098-8113 (2014).
6. Y. Yu et al., Nano Lett.14, 2778-2782 (2014).
7. J. Kim, C. Rong, J. P. Liu, S. Sun, Adv. Mater.21, 906-909 (2009).
8. M. Pousthomis et al., Nano Res. (2015), doi:10.1007/s12274-015-0734-x

Due to the recent concern about the stable supply of heavy rare earth elements (HRE), finding a way to increase the coercivity of Nd-Fe-B magnets without Dy has become the center of permanent magnet research in Japan. In this talk, we will update our recent progress toward the development of high coercivity Nd-Fe-B permanent magnets. To obtain complete understanding of the microstructure-coercivity relationships, we revisited the microstructures of Nd-Fe-B sintered and hot-deformed magnets using aberration-corrected STEM complemented by atom probe tomography (APT). In addition, we employed electron backscatter diffraction to determine the misorientation of the grain boundaries. We found that the structure and chemical composition of the grain boundary phase show strong orientation dependence, i.e., the grain boundary phase parallel to the c-planes are mostly crystalline with a higher Nd concentration in contrast to that lying parallel to the c-axis that contains higher Fe content with the amorphous structure. These investigations have suggested it is the key to decouple intergrain exchange decoupling along c-planes of anisotropy magnets. We discuss the way to achieve coercivity higher than 2.5 T based on these new results.

The Nd-Fe-B magnets with excellent properties have extended the applications in the field of motors for Hybrid Electric and Electric Vehicles. It is well known that Nd-Fe-B magnets without doping dysprosium (Dy) show a decrease of coercivity at elevated temperatures. Therefore, development of the Nd-Fe-B magnets which can use at elevated temperature is expected. In order to reduce deterioration of coercivity of Nd-Fe-B magnets at elevated temperatures, it is important to observe the generating site of reverse magnetic domains and magnetic domain wall motion in Nd-Fe-B magnets. In this study, we conducted the in-situ observations of the magnetic domain structure change in Nd-Fe-B magnets at high temperature by transmission electron microscopy (TEM) / Lorentz microscopy with applying an external magnetic field.
Fine-grained sintered Nd-Fe-B magnets without Dy were prepared using HDDR processed powders. The average grain size of Nd₂Fe₁₄B magnets was about 380 nm. Thin foils suitable for TEM observations were prepared by a focused ion beam (FIB) thinning method (Hitachi FB-2100). TEM observations were carried out in a HF-3300EH at temperatures ranging from room temperature to 225 ^oC.
Prior to observation, a thin foil was magnetized by an external magnetic field of 2.0 T to almost saturation, then the magnetic domain structures were observed by the Fresnel mode with in-situ heating. At 225 ^oC, reverse magnetic domains were found to generate in the thin foil sample without applying an external magnetic field. When we applied a magnetic field to the foil parallel to the pre-magnetization direction at 225 ^oC, the reverse magnetic domain shrank then disappeared. However, when we stopped applying the magnetic field, the reverse magnetic domain generated at almost the same position. On the other hand, when we applied a magnetic field to the foils in the opposite direction, the reverse domain started to grow, i.e., magnetic domain wall motion was observed. The motion of domain walls was discontinuous; the domain wall jumped to one grain boundary to the neighboring grain boundary indicating that grain boundaries acted as pinning sites. From the observation results obtained in this study, it was revealed that demagnetization would proceed the nucleation of reverse domains followed by the domain wall motion at 225^oC. Therefore, the pinning sites would play an important role for enhancement in coercivity at high temperature.
Acknowledgement: This work is based on results obtained from the future pioneering program "Development of magnetic material technology for high-efficiency motors" commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Micromagnets made from high-performance materials like NdFeB have gained increasing interest for MEMS applications such as vibrational energy harvesters[1], microspeakers in hearing aids[2] or magnetic actuators for micro-mirrors[3]. Since the magnetic forces scale with the volume large structures are preferred. But deposition techniques like sputtering or evaporation as commonly used in microfabrication typically provide layers with thicknesses of a few µm only. Moreover, as in the case of hard magnetic materials, often high temperatures are needed and subsequent patterning is required. The application of electroplating solves the patterning issue and enables much thicker structures, but the range of materials is very limited. An alternative approach is the use of magnetic particles to build up bulky structures. Many techniques are based on printing or molding of polymers loaded with magnetic powder[4]. However, the post processing capabilities of substrates containing such magnetic structures are limited due to the low thermal insufficient chemical stability of the organic binders.
In this work, we present a novel approach that allows the wafer-level fabrication of temperature resistant (up to at least 400°C) micromagnets compatible with standard back-end of line technology. Powders from high-energy-density permanent magnets, such as NdFeB and SrFeO, as well as soft-magnets, such as MnZn-Ferrite and Fe, were filled into cavities created by deep reactive ion etching on 8 inch silicon substrates. Subsequent atomic layer deposition has been used to bond the loose particles within the individual molds into solid three-dimensional bodies. Structures with dimensions ranging from several tenths of microns to millimeters have been demonstrated. The rigidness of the embedded magnetic bodies is high enough to survive mechanical post processing of the substrates. Free standing structures obtained after removing the surrounding silicon in XeF2 gas phase can be handled using conventional tweezers.
Magnetic properties were measured in dependency of particle size, particle distributions and heat treatments via vibrating sample magnetometry. For NdFeB structures with a fill factor of 0.5 a saturation magnetization of 500 kA/m, a remanence of 330 kA/m, and a coercivity of 680 kA/m were measured. Although the cavities were filled manually with the magnetic powder reproducibility within 5% of the material parameters have been achieved.
To evaluate the corrosion stability of NdFeB the micromagnets were exposed for one hour at 400°C to air. After remagnetization the same performance was measured as before. To protect the micromagnets during subsequent wafer processing coating with common PECVD layers is possible without any degradation.
Literature
[1] N. Wang et. al., Proc. PowerMEMS 2009
[2] S.-S. Je et. al., Proc. Transducers 2009
[4] T. Nakano et. al., Proc. LEOS Opt. MEMS and Nanophot., 2009
[5] M, Pallapa et. al, Smart Mater. Struct. 24, 025007 (2015)

In the form of Mn_3-δGa, it has been reported that the L1₀ structure δ-MnGa and the DO₂₂ structure Mn₃Ga can be obtained in the composition range of δ = 1.2-2 and δ = 0.15-1.06 respectively [1]. It is known that both the L1₀ type δ-MnGa [2] and DO₂₂ type Mn₃Ga [1] possess high magnetic anisotropy energy K in the order of 10⁷ erg/cc at room temperature. In the present work, a systematic study has been carried out in order to elucidate the relationship between magnetic properties and structure of Mn_3-δGa thin films.
Multilayer thin films [MnGa 2 nm/Mn x nm] ×25 were deposited onto silica glass substrates using DC magnetron sputtering under base pressure of approximately 10^-9 Torr. Both MnGa (50-50 at%) alloy targets and pure Mn targets were used. The composition of films was controlled by tuning each thickness of MnGa and Mn layers. The multilayers thus fabricated were post-annealed at a temperature range from 200 to 500 ^oC for 10 hours. A 5 nm thick Ru capping layer was deposited after annealing process. The magnetic properties were characterized by an alternating gradient magnetometer in fields up to 2 T and a vibrating sample magnetometer in fields up to 9 T. The structural properties were analyzed by X-ray diffraction with Cu Kα radiation and a transmission electron microscopy.
Through the control of a Mn layer thickness x in the multilayer structure, both the L1₀ type MnGa and the DO₂₂ type Mn₃Ga were successfully fabricated. The saturation magnetization (M_s) observed for L1₀ MnGa and DO₂₂ Mn₃Ga were 215 emu/cc with x = 0.5 and 100 emu/cc with x = 2, respectively. Besides, a high in-plane coercivity (H_c) of 13.5 kOe was observed for the sample with x = 3 at room temperature. In the case of sample with x = 2, in-plane H_c is about 9.2 kOe, smaller than that for x = 3.
In summary, for the first time both the L1_o and DO₂₂ phases of the MnGa have been successfully fabricated onto glass substrates, which exhibit high coercivity.
[1] H. Niida, T. Hori, H. Onodera, Y. Yamaguchi, and Y. Nakagawa, “Magnetization and coercivity of Mn_3-δGa alloys with a DO₂₂-type structure,” J. Appl. Phys., vol. 79, pp. 5946-5948, Apr. 1996.
[2] T. Bither and W. Cloud, “Magnetic Tetragonal Phase in the Mn-Ga Binary,” J. Appl. Phys., vol. 36, pp. 1501-1502, Dec. 1964.

Magnetic materials are important in the production, transmission and use of electrical energy. Advanced permanent magnets (PMs) contain rare earth (RE) elements and are used in a multitude of applications [1] that play important roles in energy-efficient, low-carbon technologies. Recent severe price fluctuations for REs have prompted the search for alternative types of magnets to functionalize specific applications. Among these alternatives, high-performance ferrites and t-phase MnAl are promising choices due to the abundance of the constituent elements and potential for good magnetic properties [2,3]. Of equal importance to the search for alternative magnets is the necessity of considering environmental issues and factory production efficiency by finding energy- and cost-efficient recycling methods.
This presentation will cover aspects related to the synthesis, processing and industrial recycling of RE-free PMs. In particular the following topics will be addressed:
Tuning microstructure of ferrites for the production of high-coercive isotropic powders.
Rapid-milling as a fast processing technique developing the magnetic performance of MnAl melt-spun ribbons.
Recycling of ferrites in manufacturing line.
Optimization of an ultrafast-milling technique has allowed us successful preparation of highly-coercive isotropic ferrites powders: Sr-ferrite (SrFe₁₂O₁₉)-based nanocomposites and single-phase Co-ferrite (CoFe₂O₄). This technique has resulted in a 3-fold increase in coercivity (1.5 kOe to 4.7 kOe) of co-precipitated Co-ferrite powders after only 3 min of milling. This large increase is attributed to a combination of a fine microstructure and stress anisotropy imparted during milling. Sr-ferrite-based powders with coercivity > 6 kOe have been also obtained using this technique, which provides some of the largest coercivity values reported for isotropic Sr-ferrite powders.
Rapid milling of MnAl for only 9 min, followed by heat treatment at 3500C, has resulted in an increase in coercivity from 1.6 to 2.4 kOe, and an increase in magnetization (under H_appl^max=2.7 T) from 42 to 60 emu/g, respectively. This improvement is attributed to an increased content of t-phase generated during processing.
The presentation will conclude with demonstration of a recycling procedure for ferrites from wastes generated in production line that has been successfully demonstrated in an industrial environment. The procedure is cost-efficient allowing to the company the reuse of ferrites from their resulting residues, i.e. improving the production efficiency, and with no need of an extra-cost for removal of this waste by an external company.
Acknowledgements: Research supported by EU-FP7 NANOPYME Project (No. 310516), ENMA Project (MAT2014-56955-R) funded by MINECO and by Northeastern University.
References
[1] L.H. Lewis et al., Metall. Mater. Trans. A44, 2-20 (2013).
[2] NANOPYME website: www.nanopyme-project.eu
[3] F. Jiménez-Villacorta et al., Metals 4, 8 (2014).

3d/4d and 3d/5d structures involving heavy transition elements have long been known to possess good permanent magnetic properties because of their ability to induce large anisotropy in structures such as L1₀ magnets. However the use of heavy transition metals such as palladium and platinum is very expensive. Thus, a comprehensive understanding and desire to develop other itinerant 3d/4d and 3d/5d permanent magnets is of utmost importance to materials scientists. Alternatives must exceed the performance of their predecessors while being cost effective. There have been reports which suggest that low content of tungsten (W) has the potential to induce large magnetocrystalline anisotropy and increase magnetization in iron (Fe) and cobalt (Co) as a result of large spin-orbit coupling of 5d elements which can lead to strong 3d/5d hybridization.
In this study, the effect of grain size of mechanically alloyed Fe₉₀X₁₀ (X=W, Ta) powders on the magnetic properties was studied. Surprisingly tantalum (Ta) has the opposite effect on magnetization of Fe compared to W. As Ta gets dissolved in the Fe lattice the coercivity tends to peak at 50 Oe after 2 hours of milling and decreases thereafter, however saturation magnetization increases where it is maximum at 141 emu/g. In contrast, a maximum coercivity of 131 Oe was achieved after 80 hours of milling and a decrease from 160 emu/g to 128 emu/g in saturation magnetization was observed with W incorporation into Fe. One way to achieve high coercivities is to optimize the microstructure such that nucleation sites are avoided, and domain walls are pinned at thin planar defects. In light of this, Fe_100-xW_x (x = 5 - 20 at.%) and Fe_100-xTa_x (x = 5 - 33 at.%) was arc-melted and used as targets to deposit thin films of different compositions on silicon wafer substrates using the pulsed laser deposition technique. The effects of film composition, post annealing temperature, and deposition temperature on the magnetic properties parallel and normal to the film plane will also be discussed.

Magnetic materials play a critical role in devices for the conversion, transmission and storage of energy. There is a growing demand for permanent magnets with better coercivity and magnetic flux thereby, it is essential to improve the alloy design and processing of permanent magnets. The most powerful and strong magnetic alloys (i.e. Fe-Nd-B, Sm-Co) contain relatively high amount of rare-earth (RE) elements. Several factors of cost and limitation on RE supply have recently motivated a greatly augmented effort on development of RE-free permanent magnets by either minimizing or completely substituting the rare-earth elements. AlNiCo magnets are among the good candidates to replace the permanent magnets with rare-earth constituents. On the other hand, its low coercivity as compared to other permanent magnets has been regarded as the major problem in AlNiCo permanent magnets. The coercivity is expected to be maximized in the single domain range. For AlNiCo based magnets this range were theoretically calculated to be between 2 to 20 nm. In this study, AlNiCo powders were synthesized by ball milling and hydrogen plasma-metal reaction system to decrease the particle size in single domain regions and thus increase the coercivity. Mechanically-milled specimens in micron-length scale, showed no change in the crystal structure indicated by the X-ray diffraction pattern but the coercivity was found to be slightly higher relative to the bulk alloy. The coercivity of nanoscale powders produced by hydrogen plasma-metal reaction was found to be 5 times higher as compared to mechanically milled specimens. TEM analysis of the plasma synthesized nanoparticles showed a core/shell structure in which AlNiCo powders were encapsulated with magnetic Fe₃O₄. Presence of Fe₃O₄, in addition to the NiAl and FeCo phases was validated from both the X-Ray diffraction pattern and the selected area diffraction pattern in TEM samples prepared by FIB technique. EDS analysis in S/TEM showed that the level of oxygen within the core and the shell changes drastically. Oxygen content is observed to be high for the shell whereas the value drops down to almost 10% for the core. This suggests that the spherical nature of the plasma synthesized nanoparticles allows the formation of the core structure encapsulated with an oxide layer. It is observed that the oxide layer covers the surface of the magnetic AlNiCo nanoparticles throughout the sample continuously. This sshows that the core/shell structure improves magnetic coercivity and the magnetic oxide layer improves the magnetic properties. The magnetic behavior of AlNiCo powders with respect to size and core-shell structure formation will be discused in details in conjuction with TEM, S/TEM, VSM and XRD results.

As it shown in [1], severe plastic deformation has a great effect on magnetic properties of 4-f elements. For instance, in gadolinium a significant increase of the magnetocrystalline anisotropy (up to 2 orders of magnitude) has been observed. Thus, it is the question - is it possible to improve coercivity in 3-d based alloys with the help of severe plastic deformation or not? In our work we have chosen the objects of the investigation based of the following reasons.
1. The meteoritic tetrataenite phase of FeNi has the outstanding magnetic properties as a rare-earth free permanent magnet, but the synthesis of this phase is extremely difficult. Stabilization of the tetrataenite phase could be possible with addition of some extra elements [2]. After preparation of rapidly quenched precursors of Fe₄₈Ni₄₈X₄ (X=Ta, Zr, W, Mo, Re) the sample Fe₄₈Ni₄₈Zr₄ shows the highest coercivity and it was the reason to select it as the first object of the investigation.
2. (Fe, Co)₂B alloys have easy-axis magnetic anisotropy and they are promising materials as the rare-earth free permanent magnets. After preparation of rapidly quenched precursors
(Fe, Co)₂B alloys with small addition of Ti, Cr, Zr, Nb and Re the highest coercivity has been observed for the composition Fe_1.5Co_0.5BTa_0.3. That was the second compound for current research.
3. In the literature, there are a few works where the magnetic properties of rapidly quenched Co₈₀Zr₁₆B₄ were investigated and an enhancement of the coercivity (up to several kOe) has been reported after a heat treatment. This compound has been selected as the third one.
HPT (Bridgemen anvils) was performed under 5GPa pressure with 5 complete turns. Such a high plastic deformation was found to dramatically affect microstructure of the samples by reduction of the grain size down to the nanometer scale. No significant change was observed for Ni₄₈Fe₄₈Zr₄ and Fe_1.5Co_0.5BTa_0.3 alloys before and after the heat treatment, but for the Co₈₀Zr₁₆B₄ sample an increase of the coercivity up to 2.25 kOe has been found. The origin of the enhanced coercivity is suggested to be due to the refined grain structure obtained during the HPT process. Thus, it is demonstrated that HPT affects magnetic properties of 3d compounds and in some cases it is possible to enhance the coercivity of these materials.
The authors gratefully acknowledge the financial support of the RF President MD-770.2014.2 grant.
[1] S.V. Taskaev, M.D. Kuz&’min, K.P. Skokov, D.Yu.Karpenkov, A.P. Pellenen, V.D. BuchelnikovandO. Gutfleisch.J. Magn. Magn. Mater.331, 33 (2013).
[2] P. Manchanda, R. Skomski, N. Bordeaux, L.H. Lewis, and A.Kashyap.J. Appl. Phys.115, 17A710 (2014).

Self-assembly provides a toolbox of techniques for the bottom-up fabrication of magnetic nanostructures with useful properties. Block copolymer nanolithography allows few-nm scale pattern formation over a large area, and the resulting polymer microdomain patterns can be transferred into magnetic thin films by liftoff, damascene or etching processes. We will show how arrays of nanoscale dots or lines may be made from magnetic films and multilayers such as Co, MnAl, and tunnel junction films, and describe their magnetic properties, including the formation of domain walls in 30 nm wide Co wires and the strong perpendicular anisotropy in MnAl dots. The available geometries of magnetic nanostructures are expanded by using templating strategies to impose long range order on the block copolymer and to make mesh patterns or complex arrangements of dots, lines and spaces. Triblock terpolymers provide access to square-symmetry and Archimedean tiling patterns, enabling non-close-packed magnetic arrays.
A second example of bottom-up nanofabrication is the formation of two-phase oxide nanocomposites by codeposition of immiscible materials. Codeposition of a magnetic spinel phase such as CoFe₂O₄ and a ferroelectric perovskite such as BiFeO₃ leads to a vertical nanocomposite with pillars of one phase embedded epitaxially in the other. This forms a multiferroic nanocomposite with applications in low-energy devices such as data storage or logic, where the data is stored in the magnetic pillars and manipulated by applying electric fields. The random positions of the pillars limits their utility, and we will show how substrate patterning can direct the nucleation to form well ordered structures with coupled magnetic and ferroelectric properties. Control in the vertical direction is also demonstrated by forming composites with modulated pillar widths or compositions. These materials provide a playground for the investigation of nanoscale magnetic, ferroelectric and multiferroic phenomena, as well as opportunities for making new microelectronic or sensing devices.

Self-assembly of molecules and nanoparticles into tailored structures is a promising strategy for production and design of materials with new functions. The spontaneous organization of the nanoscale building blocks into periodically packed structures is dictated by thermodynamic constraints and system-specific boundary conditions that commonly span a complex energy landscape.
Engineering particle interactions has a pivotal influence on the resulting structures and the quality of the mesocrystals from nanocrystalline building blocks. Early work on self-assembly of nanoparticles focused mainly on spheres, with hexagonally packed arrays being produced from monodisperse spheres and in recent years on nanoparticle arrays based on A_mB_n binary crystal structures by mixing monodisperse spheres of different sizes. Much less experimental work has been devoted on the formation of ordered arrays and full characterization of three-dimensional structures formed from nonspherical objects.
Iron oxide nanocrystals have attracted much interest for a range of applications because of the combination of tunable magnetic and controllable surface properties. Here, we show that superparamagnetic iron oxide (γ-Fe₂O₃) nanocubes with well-defined size and morphology can be assembled over areas of several micrometers into highly ordered arrays and how the three-dimensional structure can be determined by a combination of electron microscopy and grazing incidence small-angle scattering (GISAXS). Highly monodisperse oleic acid capped γ-Fe₂O₃ nanocrystals were prepared by a nonhydrolytic synthetic approach and dispersed in toluene. Slow evaporation of the solvent produced highly ordered mesocrystals extending over more than hundred micrometers in the lateral dimensions and several hundred nanometers in height.
The colloidal γ-Fe₂O₃ crystals were characterized by magnetometry and Mössbauer spectroscopy. A considerable spectral change was observed in the presence of small external magnetic fields applied perpendicular and parallel to the surface of the thin films, highlighting the possibility of attaining a static magnetic spectrum at low applied magnetic fields at room temperature. Application of external magnetic field can influence the interaction between magnetic nanoparticles and induce a magnetic ordering in thin films. The optical transparency of the hybrid thin films is an advantage that can be used to fabricate opto-magnetic devices and recording media.

CoFe₂O₄ based magnetic thin films play a key role in various applications in the field of magnetic and magneto-optical recording, waveguides and magnetoelectric composites due to its attractive magnetic properties such as high coercivity, anisotropy, and magnetostriction¹ combined with its insulating electronic nature. Nanostructured CoFe₂O₄ is of particular importance for magnetic recording due to increased bit storage and improved signal to noise ratios for magneto-optical applications. In this work, dispersions of BaTiO₃-CoFe₂O₄ and CoFe₂O₄-SiO₂ nanoparticles are used to fabricate composite thin film assemblies for magneto-electric and magneto-optical applications. Nanoparticle dispersions of BaTiO₃-CoFe₂O₄ are fabricated via an efficient microwave assisted non-aqueous sol gel route and the SiO₂ dispersions are synthesized via Stoeber process. The dispersions are then further assembled into corresponding thin film composite geometries through sequential spin coating-drying steps followed by sintering. Structural and microstructural examinations on both BaTiO₃-CoFe₂O₄ and CoFe₂O₄-SiO₂ composites revealed the formation of several hundred nanometer thick and crack free thin films of desired phases with maintained nanogranular structure after sintering. To investigate the magnetic characteristics of the magneto-electric composites, in plane and out of plane hysteresis loops as well as zero field cooling and field cooling tests were carried out. In addition, synchrotron based x-ray magnetic circular dichroism technique at Fe, Co and Ti L₃ edges is employed to gain elemental insights into the magnetism of the BaTiO₃-CoFe₂O₄ composites for various BaTiO₃-to-CoFe₂O₄ ratios. For CoFe₂O₄-SiO₂ composites, we found that optical properties such as band gap and refractive index can be effectively tuned upon SiO₂ addition. In-plane magnetic characteristics of these films showed a superparamagnetic nature whereas polar Kerr rotation measurements revealed considerable magneto-optical hysteresis, which implies presence of perpendicular magnetic anisotropy. In this manner, we show that through sintering associated in-plane tensile stresses and negative magnetostriction of CoFe₂O₄, perpendicular magnetic anisotropy can be induced in these composites despite a fully isotropic nanoparticulate nature with ferromagnetic characteristics being preserved up to 50 wt% SiO₂ content. In conclusion, liquid phase thin film deposition using preformed nanoparticles can be effectively used to fabricate thin film composites of various compositions and different composite geometries with perpendicular magnetic anisotropy for magnetic, magneto-electric and magneto-optical applications.
1.Yanagihara, H.; Utsumi, Y.; Niizeki, T.; Inoue, J.; Kita, E., Perpendicular magnetic anisotropy in epitaxially strained cobalt-ferrite (001) thin films. J. Appl. Phys. 2014, 115, 17A719.

In this work we present a study about the magnetic properties of Co₃O₄ polycrystals with large size distribution. Co₃O₄ has technological importance principally due to their applications in Lithium batteries. This oxide has a spinel structure in which Co³⁺ ions occupy octahedral sites and do not contribute to the magnetic properties while the Co²⁺ ions in tetrahedral sites are arranged antiferromagnetically below T_N~30K[1].
Our crystals were synthesized by Pechini Method. CoSO₄.7H₂O was used as precursor and the resin obtained was calcinated at 800°C during 3 hours. The sample microstructure was investigated using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) measurements. Magnetic susceptibility (chi; and chi;') as a function of applied magnetic field (H) and as a function of temperature (T) in the range of 1.8K-300K measurements were performed using a SQUID-VSM magnetometer.
Cubic Co₃O₄ (ICSD Code:24210) is the only phase present in the sample and SEM image showed particles with diameter between 100nm and 1200nm, with 68nm of crystallite size on average. In chi; versus T data two peaks are evident, the first, at T_f=14K (freezing temperature) has a remarkable response to H, disappearing for Hge;35kOe and the second T_N=32K is well described in the literature as being the Néel temperature for Co₃O₄ bulk. As chi; versus T measurements are efficient to determine the freezing temperature but are not sufficient to investigate its nature we performed chi;' versus T measurements for a driven field H_AC=10 Oe and H_DC=0 Oe. In these analysis we observed that the peak at~32K is kept fixed by varying the driven frequency, in accordance with a transition characteristic of the antiferromagnetic material, although, as a result of frustration, the maximum at 14K presents an increase of intensity as higher is the driven frequency. Furthermore, an increase of chi; values for temperatures below T_f was also observed and is associated to uncompensated moments on the nanocrystals surface. The system also presented an exponential relaxation for remanent magnetization and two distinct behaviors in the M/H versus H curves. Around T_f there is an decrease of M/H values as H is increased, although, the same starts increasing around 4.5kOe reaching a plateau at 55kOe. Around T_N the M/H values decrease for all H range and the curve also reaches a plateau which is close to that observed for M/H values around T_f, however less intense.
Analyzing these data we suggest that below T_f the system is in a metastable state in which there is a competition between uncompensated superficial moments and the moments associated to the antiferromagnetic bulk portion, an result of changes in the particles surface attributed to the particle size reduction[2]. Results showed that the metastable state is dependent not only on temperature but also on applied fields.
[1] J. Phys. Chem. Solids, vol. 25, pp. 1-10,1964.
[2] J. Appl. Phys.,vol. 102, p. 103911, 2007.
Acknowledgments: CNPq and FAPESP.

Self-assembled nanocomposites of itinerant ferromagnetic SrRuO₃ (SRO) and superconducting YBa₂Cu₃O₇ (YBCO) as nano crystallites and matrix, respectively are sythesized and the nanocomposites so formed are structurally phase separate. We are able to demonstrate metal to insulator transition in the normal state of YBCO (the high temperature regime of YBCO-SRO nanostructures) and a crossover between superconductivity and magnetism at low temperatures with increased concentrations of SRO in YBCO matrix. Starting from a much diluted concentration of SRO in YBCO-SRO nanocomposites, which exhibits an insulating phase at high temperatures and superconducting phase at low temperatures, by increasing the magnetic interactions as a function of SRO doping, we investigated the electronic correlations and the interplay between superconductivity and magnetism throughout the temperature regime. A crossover from the superconducting phase to the magnetic phase with increasing density of nano-size SRO crystallites in the YBCO matrix is observed as a consequence of competing interactions between these two ordered phases.

Ferrites thin films have a number of technological applications in areas such as telecommunications (microwave and millimeter wave devices), magneto-electric coupling devices, and are also promising candidates for future spintronic devices. Properties such as higher resistivity leading to lower eddy current loss, high saturation magnetization and Neel temperature, and low magnetic losses make spinel and hexa-ferrites attractive materials for high frequency applications. Ferromagnetic resonance (FMR) has proved to be an excellent tool to study various relaxation mechanisms in high frequency magnetic material applications.
Traditionally, epitaxial thin film of NiFe₂O₄ films have been deposited on a variety of substrates such as SrTiO₃, MgO, MgAl₂O_4shy;, Al₂O₃ etc., all having a lattice mismatch of ~3-10% with NiFe₂O₄. These films normally exhibit low saturation magnetization and at least an order of higher magnitude ferromagnetic resonance (FMR) linewidth as compared to NiFe₂O₄ bulk single crystal. A higher value of lattice mismatch and a chemically incompatible substrate crystal structure lead to degraded magnetic properties primarily due to development of antiphase boundaries in ferrite thin films.
We have used single crystal MgGa₂O₄ substrate, which has a spinel structure similar to that of NiFe₂O₄ and an extremely small lattice mismatch (~0.6 %), to deposit NiFe₂O₄ films using pulsed laser deposition technique. TEM studies show absence of antiphase boundaries, a defect always present in ferrite films deposited on other substrates. We obtain FMR linewidths at least one order of magnitude smaller than the previously reported values at comparable frequencies and film thickness, e.g., for a frequency of 10 GHz we obtain a linewidth of ~32 Oe for a 450 nm film. These FMR linewidths are comparable to that of bulk single crystal NiFe₂O₄. More importantly, we obtain a linear variation of the linewidth with microwave frequency and are able to determine the value of Gilbert damping parameter as 0.002. The details of film deposition, structural, magnetic and ferromagnetic resonance characterization, along with a comparison of physical and magnetic properties of same film deposited on a different substrate (MgAl₂O₄) will be presented.

Iron nitride thin films may have wide applications in both biomedical and energy applications. The magnetic properties of these films can be tuned or modified by incorporating copper nitride in the thin films of iron nitride by varying the iron to copper ratio in the film. Similarly, by systematically changing other fabrication parameters, the magnetic properties of these films can be tuned for desired applications. In this study, iron copper nitride thin films have been fabricated by RF/DC magnetron sputtering technique, either by co-sputtering iron and copper in the presence of ambient Ar+N₂ or layer stacking of iron nitride and copper nitride layers. The fabrication conditions namely substrate temperature, nitrogen partial pressure and iron and copper sputter powers have been varied systematically during fabrication and its impact on structure, composition and magnetic properties of the films has been studied. X-ray diffraction has been used to study the structure of the as-fabricated films and their thickness and density are estimated using x-ray reflectivity measurements, along with scanning electron microscope measurements. The relative compositions of iron, copper and nitrogen in the films have been determined using x-ray photoelectron spectroscopy. Finally, the magnetic properties of the films have been measured using a vibration sample magnetometer and these results have been correlated with growth, structure and composition of the films.

Among Mn-X alloys, the low temperature phase (LTP) MnBi (NiAs type), L1₀MnAl (tau;-phase), and L1₀MnGa (δ-phase) possess the high magnetic anisotropy constant K (10⁷erg/cc at 300K). The anomalous temperature dependence of magnetic anisotropy that increases with temperature T for a temperature range from about 100 to 500K [1,2] has been the subject for many workers. Some recent theoretical works showed the close correlation between magnetic anisotropy energy and lattice constant [3]. However, the experimental results are not well explained by those theories, and the magnetic anisotropy mechanism is still open for question. A recent experimental work on the LTP MnBi thin films showed the correlation between K and saturation magnetization M_s that the K inversely proportional to M_s with a power of eight [4]. Very few theoretical work has been found in literature to account for this experimental result. In the case of tau;-phase MnAl, a theoretical work showed that the effective shy;spin orbit coupling constant is much larger than those for individual Mn and Al atoms, almost one order of magnitude [5], leading to a large magnetic anisotropy. A recent work in tau;-phase MnAl thin films showed the linear dependence of K on T [6]. This result is at variance with the theoretical prediction put forward.
A systematic study on the temperature dependence of magnetic anisotropy in MnX alloys (X=Bi,Al,Ga) fabricated onto silica glass and single crystal (MgO and SrTiO₃) substrates has been carried out. Multilayers of (Mn(x nm)/Bi, Al, Ga (y nm)) x N were first deposited onto substrates, followed by an annealing process at temperatures T_a for annealing time t_a. Measurements of magnetic properties were carried out by using VSM in fields up to 90 kOe. Structural characterizations were conducted by XRD and TEM.
For LTP MnBi thin films, there is a distinctive difference in morphology between those films onto glass substrates and single crystals. This change in morphology reflects a significant difference in magnetic properties, such as magnetic anisotropy and coercivity. It is found that the structural transformation of MnGa thin films from L1₀ to DO₂₂ phase has been successfully controlled by changing Mn thickness x. The present talk will present the results of magnetic anisotropy of those compounds in conjunction with structure.
The work was partially supported by NSF-CMMI 1229049 and TDK.
References:
1. C. Guillaud, Ph.D. thesis, University of Strasbourg, Strassbourg,1943.
2. T. Chen and W. Stutius, IEEE Trans. Magn. 10, 581 (1974).
3. N.A.Zarkevich, L.-L.Wang, and D.D. Johnson : App. Phys. Lett., Materials, 2,032103-1 (2014).
4. T.Suzuki,T. Hozumi et al.: IEEE Trans.Magn.(Accepted for publication).
5. A.Sakuma, Y.Manabe and Y.Kota : J. Phys. Soc. Jpn., 82, pp. 073704-1 (2013).
6. S.Zhao, T.Suzuki et al.: IEEE Trans. Magn.(Accepted for publication).

Nanocrystalline metals have led to widespread interest ranging from magnetic, catalytic and energy applications. It has generated great desire to grow nanoalloys with controlled properties and well-defined structures on the atomic scale coupled with flexibility. A new synthetic scheme of nanoalloys which avoids incompatible reduction potentials and rates would be critical to grow high purity and stoichiometry metal nanostructures. Here, I will report the metal-redox strategy through a spontaneous oxidation-reduction reaction to grow nanocrystalline alloys using molecular-scale zerovalent metal resources. Selection of proper zerovalent metal species, allows for chemical thermodynamic control of the compositional stoichiometry during the temperature-dependent nanoalloying reactions. These findings demonstrate a practical and scalable strategy for magnetic nanoalloy growth, and can potentially produce key metal components of superior metallurgical quality for catalytic and magnetic systems.

Heusler alloys draw increasing attention due to their attractive electrical, magnetic and optical properties for new generation electronics and spintronics [1, 2, 3]. It is a large and diverse class of crystalline cubic materials made of three constituting metallic or semi-metallic elements. Depending on the elements chosen and application desired, one can prepare a half#8209;metallic ferromagnet, semiconductor, topological insulator or others. Both Rh2MnAl and Rh2MnBi are ferromagnetic [2, 3].
To fully exploit the properties of Heusler alloys, a sufficient level of their material qualities has to be reached and hence their growth process understood [1, 2]. We studied the growth process and its effect on the resulting properties of Rh2MnAl and Rh2MnBi thin films. The films were deposited in a UHV sputtering chamber using a MgO(100) substrate mounted on a holder with controlled heating. The substrate should provide suitable conditions for epitaxial growth due to high lattices match. Deposition from compound targets mostly leads to deviations from stoichiometry in the prepared film. Thus, three individually controlled magnetrons with single metal targets were operated simultaneously in a DC Ar plasma. Targeted thickness of the films was 300 nm. Prepared samples were characterized by several microscopic and spectroscopic techniques - AFM, SEM-EDX, XPS, XRD. Magnetic behavior of the samples was investigated by a vibrating sample magnetometer.
Diverse combinations of plasma pressure, substrate temperature, power applied to the magnetrons and deposition duration was tested. Demanded purity and stoichiometry was achieved conveniently. Room-temperature deposited films are amorphous, as clarified by XRD, and their surface was typical with a spongy morphology. As anticipated, the surface morphology changed and the material crystallized after the deposition at 600°C (Rh2MnAl) and 400°C (Rh2MnBi). The sample surface was composed of well defined and densely organized nanocrystallites, as observed by SEM and AFM. Although the epitaxial growth of the films was successful, the path to produce the desired L21 superstructure remains complex, as inferred from diffraction patterns. In other words, the prepared films suffered from structure disorder. However, this is not uncommon for full Heusler alloys [1].
Ferromagnetic behavior of both alloys was confirmed but the measured magnetization was low which may reflect structure disorder [1]. It is also possible that the lower values are caused by a relatively rough surface morphology which induces undesirable surface states.
[1] T. Graf, S. S. P. Parkin, C. Felser, IEEE Transactions on Magnetics 47 (2011) 367.
[2] M. Gilleszlig;en, R. Dronskowski, Journal of Computational Chemistry 30 (2008) 1290.
[3] I. Galanakis, P. H. Dederichs, N. Papanikolaou, Physical Review B 66 (2002) 174429.

Iron oxide magnetic vortex nanoparticles are appealing for biological applications because of their biocompatibility and excellent colloidal properties. The vortex state possessed by these particles prevents them from being attracting to each other and aggregating. Furthermore, their magnetic shape anisotropy makes them ideally suited for transducing magnetic torque to cell membranes upon application of static magnetic fields or for heating cells in AC magnetic fields. In this work, iron oxide magnetic vortex nanoparticles are synthesized and functionalized for the application of modulating voltages across the neural cell membrane. In addition, micromagnetic simulation is used to explore the magnetic phases of tertiary ferrite (AFe₂O₄, A = Mn, Zn) magnetic vortex nanoparticles as a function of geometry and doping. Neurons are chosen as a biological testbed for this project because the amplification mechanism of action potentials allows these cells to respond robustly to the small inputs applied by nanoparticles.

The large scale production of contrast agents for bio-imaging is a key requirement for their successful clinical application. Here, highly magnetic Zn_0.4Fe_2.6O₄ nanoparticles were produced via scalable and dry flame spray pyrolysis in a single process step. The size of these non-stoichiometric Zn-ferrites was precisely controlled from 7 to 57 nm. Crystallinity as well as magnetic properties were carefully addressed and a clear size dependence was shown. The produced nanostructures showed an extraordinary room temperature saturation magnetization of up to 71 emu/g. Special emphasis was put on their application as contrast agents for magnetic resonance imaging. A maximum r2 relaxivity of 403 s^-1 mM^-1 (Zn+Fe) was reported. Further, their potential as therapeutic hyperthermia agents was investigated. Here the dependence of the heating efficiency on the particle size and magnetic properties was analyzed and the requirement of a strong superparamagnetism in the sample was shown.

According to the American Cancer Society, an estimated 231,840 new cases of breast cancer are expected to occur among women during 2015. Despite successful treatment of the primary malignancy, relapse and subsequent metastatic spread can still occur at distant sites, including bone, lungs, liver, and brain. Out of which 80% to 90% of breast cancer metastasized and signals the entry of the disease into an incurable phase. To date, limited treatment options exist for breast cancer metastasis to bone. The difficulty of eliminating bone-residing cancer necessitates an alternative novel diagnostic combinatorial treatment regimen to manipulate drug resistance and microenvironment of tumor cells with minimal off-target effects. To this end, we engineered multifunctional theranostics nanomedicine (MTNs) made up of poly(lactic-co-glycolic acid) (PLGA) core containing therapeutic doxorubicin (DOX), higher density of super-paramagnetic iron oxide nanoparticles (SPIOs (5nm), and decorated peripherally by Bisphosphonate. Bisphosphonate, Alendronic acid, used herein targets the bone mineral (Ca²⁺ ion) and also has been used clinically for the treatment of bone related diseases. These MTNs were characterized by their hydrodynamic diameter of 100 ± 5 nm and longer blood circulation half-lives with the higher loading of SPIOs and DOX. Analysis by Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) and Ultraviolet Visible Spectrophotometer (UV-Vis) revealed 70 µg/mL of SPIOs and 7% by weight of DOX were encapsulated into 1 mg of MTNs. Transmission electron micrographs (TEM) showed that SPIOs were well packed and embedded into the core of the MTNs, which in turn exhibited the magnetic relaxivity r₂ of 400 mM^-1s^-1 (at 14 Tesla magnetic strength), which is an order of magnitude higher than that of iron oxide based clinically used magnetic contrast agents such as Feridex^® (r₂ = 120 mM^-1s^-1) and Supravist^® (r₂ = 57 mM^-1s^-1). In 10 minutes of magnetic induction heating, it was found that the temperature raised to 45 °C in a bulk suspension. Such a rapid elevation of temperature of the nano suspension realizes us to believe that the local temperature at the nanomedicine core would be higher enough to release the drug rapidly at tumor site. Due to the multi-functionality and higher magnetic relaxivity, MTNs would hold a promise in multimodal treatment of metastatic breast cancer to bone by limiting off target effect.

One of the most popular functional magnetic materials with various applications including multi-tera bit storage device, catalysis, sensors, and a platform for high-sensitivity biomolecular magnetic resonance imaging (MRI) for medical diagnosis. We developed a facile route to magnetic iron oxide nanoparticles synthesized by reacting Fe(II) salt with alkylamine in the presence of polyethyleneimine (PEI) in an aqueous-phase at the relatively low temperature of 95 0C without any post-treatment such as calcination and heating in an autoclave. We also studied the roles of alkylamine and PEI in the formation of iron oxide nanoparticles. The synthesized iron oxide nanoparticles were then characterized by using TEM, XRD, XPS, FTIR, and superconducting quantum interference device (SQUID) magnetometer. The synthesized iron oxide nanoparticles have octahedron shape and narrow size distribution. After the surface modification using the polyethylene glycol (PEG), PEG-stabilized nanoparticles showed lower cytotoxicity than PEI-particles, demonstrating these biocompatible iron oxide nanoparticles could have beautiful various applications including biomedical imaging, diagnostics, and therapeutics.

Iron oxide nanoparticles often possess superparamagnetic properties, which in turn makes them attractive for a variety of engineering and biomedical applications (i.e. in diagnosis and therapy as drug specific delivery systems or hyperthermia treatment of cancer). Several synthesis methods have been developed: chemical co-precipitation, thermal decomposition of organic solvents, sol-gel, micelle inverse among others. A fast and facile method of alternative synthesis environment-friendly is proposed in order to obtain Fe₃O₄ (magnetite) nanoparticles from plant biomass extracts of Cinnamomun verum, NaturalVanilla sp. (pod) and synthetic vanilla extract. Reducing agents like phenolic compounds from aqueous plants extracts have been used to yield magnetic nanoparticles as fast, easy and economically viable process. This method avoids the use of expensive equipment, and hazardous chemicals, requiring a subsequent removal to diminish nanoparticles toxicity for biomedical application. Fe₃O₄, MNPs were obtained by bio-reduction and identified by XRD (PDF-19-0629) corresponding to an inverse spatial group Fd3m (227) inverse spinel FCC structure. Lattice parameters were a=8.366 Å in C. verum, a= 8.355 Å in synthetic vanilla and a= 8.3632 Å in Vanilla sp. IR peaks at 576 cm^-1 correspond to Fe-O bonding formation; while the vibrational peaks at 576-1641 and 3415 cm^-1 suggest phenol molecules involved in bio-reduction process. XRD and HRTEM diffraction patterns overlapping were corresponding with Fe₃O₄ peaks (220),(311),(400),(511), and (440). The d spacing 2.4 Å in Vanilla sp. and 2.7 Å in C. verum match the main diffraction plane (311) 2theta;= 35° in both analysis. The particle size calculated by Scherrer's equation (t=Kl/b cos #415;) in Vanilla sp. was 12 nm and 14 nm in C. verum. AFM-MFM data show a monodomain arrangement of 2-3 nm in Vanilla sp. and 5-6 nm in C. verum. VSM data indicate that magnetization increases rather using C. verum extract (64.89 emu/g) than Vanilla sp. (46.6 emu/g). The bio-synthesis of Fe₃O₄ MNPs obtained by aqueous plant extracts are commensurable to those obtained by a chemical method.
The authors thank to CINVESTAV-IPN, CONACyT for their financial support, and Lotto-Bionanolab-Conacyt-CINVESTAV-IPN Project 211506.
Keywords: Fe₃O₄ nanoparticles, bio-reduction, plant extracts.
References.
[1] G. Canizal, P. Schabes-Retchkiman. 2006. Materials Chem and Phys 97:321-329.
[2] R. Herrera-Becerra. 2010. Appl Phys A 100: 453-459.
[3] G. Rosano-Ortega, P. Schabes-Retchkiman, C. 2006. Ame Sci Pub 6:1.
[4] T. Liu, J. Wang, J. 2013. Col & Surf A: Physicochem Eng Aspects 436:675.
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Modern probe based applicators are becoming increasingly important for cancer treatment because they are localized and less invasive treatment options. Currently, the most widely used is radiofrequency ablation (RFA). However, issues related to heat sink effect, charring and an unreliable contact between the RFA probe active tip and biological media lead to decreased lesion sizes. In this study, a novel magnetic heating probe that has the potential to overcome these challenges and also increase efficacy of treatment is proposed and analysed. The probe is essentially a cannula with two main parts: a distal heat-generating tip made of a magnetic nanocomposite and a proximal insulated shaft. A description of the concept and functional operation of the probe is presented. In an effort to assess its feasibility, we evaluated the ability of probe tip (made of PMMA-Fe₃O₄ nanocomposite) to generate heat in biological tissue using alternating magnetic field parameters (field strength and frequency) that are acceptable for human use. Heat generation by MNPs was determined using the linear response theory. The effects of device properties and treatment parameters on the thermal dose were studied. Lesions were revealed to have an ellipsoidal shape and their sizes were affected by treatment time. However, their shapes remained unchanged. Furthermore, our numerical predictions also showed reasonable agreement with the experimental results previously reported in the literature. Our predictions demonstrate the feasibility of our novel probe to achieve reasonable lesion sizes, during hyperthermic or ablative heating using AMF parameters (field strength and frequency) that are acceptable for human use.

Keywords: Magnetite, magnetic nanoparticles, hydrothermal synthesis.
In the last decades, the synthesis of magnetic nanoparticles has been intensively pursued because of their many technology possibilities. Indeed, the reduction of the size to the nanometer scale has led to the discovery of novel and extraordinary properties with found many applications in various technological fields.
Fe₃O₄ nanoparticles have attracted much interest recently due to their magnetic properties and potential application in different areas ⁽¹⁾, such as supercapacitors electrode materials ⁽¹⁾, heavy metal adsorption ⁽²⁾, magnetic carriers for protein separation ⁽³⁾, etc. Moreover these magnetic nanoparticles with various controlled morphologies may have some unique physical and chemical properties, such as a specific surface area and unique lattice plane.
To date, a variety of Fe₃O₄ nanoparticles with various morphologies, include sphere, cube, wire, core-shell, have been synthesized ⁽⁴⁾. However, most of this literature only focuses on one kind of morphology. In this work, we developed a simple and environmentally friendly method in order to prepare stable Fe₃O₄ nanoparticles with controlled morphologies including sheet, octahedron, cubes and spheroids in the same conditions of synthesis. The morphologies of these nanoparticles are controlled through simply adjusting the reaction temperature.
Acknowledgment.
Financial support of this work from the Autonomous University of the State of Mexico, Grant 3688/2014/CIB is gratefully acknowledged. We also thank Lizbeth Triana Cruz and Marco Antonio Camacho Loacute;pez from CCIQS for technical assistance in IR and Raman Spectroscopy Studies.
References
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Abstract
Multifunctional magnetic nanoparticles exhibit diverse range of applications ranging from optoelectronic and energy-related devices to biomedical usage, especially in hyperthermic treatment of cancerous cells and magnetic resonance imaging. In this respect, bifunctional Au-Fe₃O₄ nanoparticles have been sought after due to their excellent surface chemistry characteristics, optical nature, superparamagnetic properties, as well as the biocompatibility offered by Au which can be used as an anchor point for biofunctionalization. Specifically, these multifunctional magnetic nanoparticles hold a lot of promise for hyperthermia treatment of cancerous tissue. These superparamagnetic can be injected into the cancerous tissue, where they can possibly lead to the necrosis of the cancerous by releasing heat under the application the application of an alternating magnetic field. Au-Fe₃O₄ nanoparticles can also be used in magnetic imaging studies as contrast enhancing agents. In this presentation we will discuss about the synthesis, magnetic property and functionalization of Au-Fe₃O₄ composite nanoparticles along with in vitro magnetic imaging studies. Superparamagnetic Au-Fe₃O₄ bifunctional nanoparticles were synthesized using a single step hot-injection precipitation method using Fe(CO)₅ as iron precursor and HAuCl₄ as gold precursor in presence of oleylamine and oleic acid while, Triton^® X-100 was employed as a highly viscous solvent to prevent agglomeration of Fe₃O₄ nanoparticles. Detailed characterization of these nanoparticles was performed by using X-ray powder diffraction, transmission electron microscopy, scanning tunneling electron microscopy, UV-visible spectroscopy, Mössbauer and magnetometry studies. Magnetic measurements also indicated that these nanoparticles were superparamagnetic in nature due to Fe₃O₄ region. The saturation magnetization for the bifunctional nanoparticles was observed to be ~74 emu/g which is significantly higher than the previously reported Fe₃O₄ nanoparticles, suggesting that these multifunctional magnetic nanoparticles might offer a better hyperthermic efficiency. Biofunctionalization of these nanoparticles were achieved by attaching L-cysteine, EGCG, polylysine, and polycapronoloactone. The cysteine functionalized Au-Fe₃O₄ bifunctional nanoparticles showed no significant cytotoxicity to the CHO cells up to 48 h even at concentrations of 1 mg/ml making them suitable for biomedical applications such as local heat generators (hyperthermia) for cancer treatment and drug delivery vehicles.

Long blood circulation time and biocompatibility, without compromising on the contrast efficacy are a pre-requisite for the fabrication of MRI contrast agents. We have successfully fabricated hydrophilic polyvinyl pyrrolidone (PVP) coated gadolinium oxide (Gd2O3) nanoparticles for T1-weighted MR imaging. PVP-Gd2O3 nanoparticles showed a reduced longitudinal T₁ relaxation time and an improved longitudinal relaxivity (r₁) of 12.1 mm^minus;1 s^minus;1 at 7 T. The in vitro studies on Hamster Kidney (HK-2) cell lines show a cell viability of upto 140% and in vivo MR imaging studies in 6 weeks old SCID mice show a constant signal for almost 12 minutes. Inorder to prolong the biocompatibility and blood circulation, so as to improve the signal enhancement, we have conjugated Bovine Serum albumin (BSA) over Gd2O3 nanoparticles. Ultra-small oleic acid capped Gd2O3 nanoparticles of average size 2.9 nm were synthesized and converted into hydrophilic phase by surface coating with mercaptoethanoic acid through ligand exchange mechanism. BSA was conjugated over the hydrophilic Gd2O3 nanoparticles by strong covalent amide bond formation. The average size of the BSA-Gd2O3 nanoparticles was found to be 21 nm. This uniform linkage of Gd2O3 nanoparticles onto the BSA chains improves the signal contrast. Since albumin is the most abundantly occurring protein in the mammalian physiology, BSA-Gd2O3 nanoparticles show better stealth characteristics and hence evade the immune response, thereby prolonging the blood circulation time. We report the successful fabrication of PVP-Gd2O3 nanoparticles for improved T1 weighted MR imaging and BSA-Gd2O3 nanoparticles for pro-longed circulation time, without compromising on the contrast efficacy.

Magnetic hyperthermia is a fast emerging, non-invasive and promising cancer treatment strategy. We have attempted to address the current challenges of the same, viz, improved biocompatibility and enhanced heating characteristics, through a single combinatorial approach. For comparison studies, both superparamagnetic iron oxide nanoparticles (SPIONs) and ferrimagnetic iron oxide nanopaticles (FIONs) of sizes 10 nm and 30 nm respectively were synthesized by thermal decomposition method. Two different surface modifying agents, viz, Cetyl Trimethyl Ammonium Bromide (CTAB) and 3-Aminopropyltrimethoxysilane (APTMS) were used to convert the as-synthesized hydrophobic iron oxide nanoparticles to hydrophilic phase and to conjugate Bovine Serum Albumin (BSA) over the iron oxide nanoparticles via two different methods, viz, surface charge adsorption and covalent amide bonding respectively. The haemolysis studies on erythrocytes show that the haemolytic index of BSA-FIONs is <2% and the cell viability of Baby Hamster Kidney (BHK) cells is upto 120%. Thus BSA-FIONs render better biocompatibility and blood circulation. It is observed from the results that, irrespective of the type of surface modifying agent and the method of conjugation, the Specific Absorption Rate (SAR) value of the BSA-FIONs is 2300 W/g when compared to 1700 W/g for FIONs without BSA. This is due to the prevention of agglomeration and improved heating characteristics imparted by BSA. It is evident from the reported results that BSA conjugation over the FIONs (with high saturation magnetization of around 85 emu/g) provides a single combinatorial approach to significantly improve the biocompatibility and also enhance the SAR value for clinical magnetic hyperthermia. To our knowldge this is the first attempt to address both the pressing challenges in magnetic hyperthermia, through a single strategy.

Surface functionalization of nanoparticles has been performed as a strategy to attain the desired response for therapeutic and diagnostic applications. We herein report the facile synthesis of superparamagnetic iron oxide nanoribbons (SPIONRs) comparatively monitoring their functionalization in water with three ligands (i.e., dextran, polyethylene glycol (PEG) and chitosan), in order to endow them with enhanced colloidal stability. Our findings indicate that PEG ligand facilitates an enhanced colloidal stabilization enabling the cationic molecules to be firmly adsorbed on the anionic SPIOs surfaces via electrostatic interactions. It was observed that the nanoribbons exhibit large exposed active surface areas for a more effective targeting of ligands and cell receptors, thus promoting multivalent interactions. The relaxivity and cytotoxicity assessment of SPIONRs on HeLa cells and Jurkat T lymphocyte cells will be also discussed.

Bifunctional magnetic and luminescent materials have important role in many applications in biological system because of the combination of two properties in the same particle. Superparamagnetic iron oxide nanoparticles as magnetite and maghemite have high magnetization of saturation and a luminescent complex can act like as temperature sensor. A strategy to combine these compounds in a same system is coating functionalized silica. It is important that interaction between luminescent complex and silica shell be a chemical bonding to prevent leaching of the complex. In this study we present a synthesis of a magnetoluminescent system constituted of magnetite nanoparticles coated with a functionalized mesoporous silica and a europium complex [Eu(tta)₃(adppo)₂] covalently linked. The iron oxide particles were synthesized by modified solvothermal strategy and provided 100 nm spherical nanoparticles. The magnetite phase was identified by XRD and FTIR measurements. It is found that particles have a high magnetization of saturation in 85 emu g^-1, with low hysteresis, characterizing superparamagnetic behavior. Mesoporous silica shell was carried out surface-protected etching process and it was subsequently silicon hydride-functionalized (Si-H). TEM images reveal that core-shell system was obtained with a 40 nm diameter porous shell, exhibiting high surface area (209 cm² g^-1). The europium complex linkage was performed by hydrosilylation reaction between Si-H groups on silica surface and allyl of the ligand in complex. The luminescence emission and excitation spectra showed the pattern of europium ion which reveals the presence of the luminescent complex in the system. Lifetime emission monitoring the more intense signal of europium (⁵D₀—⁷F₂) was 0.30 ms at room temperature. It is possible to obtain a temperature sensor by monitoring of the lifetime as function of temperature. We obtained a promising magnetic and luminescent hybrid system with potential for biological applications.

Magnetic field sensorics are extensively used for magnetic data storage, navigation, bio analysis, position tracking, nondestructive testing, and geomagnetic discovery. Recently, magnetoelectronics was applied for noninvasive investigations of the human body¹. Superconducting quantum interference devices (SQUID) represent a conventional magneto-encephalography device. These systems have a vast importance in neurological disease treatment but rather high fabrication and maintenance costs limiting their wide spread applicability. High cost is defined by a cryogenic helium cooling system required for operation of SQUID-based sensorics. Furthermore, the sensory elements cannot be located in the proximity to the object of investigation, e.g. human brain.
The development of high-performance magnetic sensors has benefited from the discovery of the new effect in metal-based amorphous wires² known as the giant magneto-impedance (GMI). The key feature of GMI sensorics is their high sensitivity to pT magnetic fields while operating at room temperature. Low price and high universality suggest extensive applications of GMI devices for bio-magnetic field detection. However, a viable technology needs to be developed to produce arrays of compact GMI sensing elements in a CMOS compatible way.
Here, we apply strain engineering^3,4 to realize arrays of GMI sensors, which are directly on-chip integratable. For the latter, we put forth a new platform relying on photopatternable, stable imide and acrylic polymers allowing for auto-assembly of the planar NiFe/Cu-based structures into 3D architectures possessing the GMI functionality. The self-assembly is triggered by an external stimulus, i.e. humidity. The process is CMOS compatible and allows integrating multiple functional elements including pick-up coils and GMI sensors into a single tube. The integration aspect is absolutely crucial to enable successful detection of small signals as the sensor response can be directly conditioned using advanced silicon electronics. The typical length of the tube is in the mm range with diameters of some tens of µm. Careful characterization of the GMI sensing elements before and after the self-assembly process reveals that their magnetoelectrical performance is drastically improved (80x) when transformed from the planar into the 3D architectures. The pick-up coil enhances the sensitivity and boosts the signal-to-noise ratio of the devices. Compact GMI sensors equipped with pick-up coils operate at ambient conditions and demonstrate very high sensitivity to external magnetic fields.
In this contribution, the fabrication and characterization of the novel GMI platform will be presented. The potential of these sensorics for magneto-encephalography applications will be highlighted.
References:
1. Funke, M. E. et al.Epilepsia52, (2011).
2. Nakayama, S. et al.PLoS One6, (2011).
3. Mei, Y. et al.Adv. Mater.20, (2008).
4. Ionov, L. Mater. Today17, (2014).

Bulk cobalt ferrite (CoF) has high permeability, high saturation magnetization, low magnetostriction and high magnetocrystalline anisotropy, and high electrical resistivity that ensures low eddy currents. Though these properties make CoF a candidate material for high frequency applications, its high coercivity leads to hysteresis losses. We have therefore prepared and examined the magnetic and electrochemical characteristics of nanostructured CoF, with a view, respectively, to applying CoF in hyperthermia and in energy storage. Nanocrystalline CoF, both in powder and thin film form, could be synthesised in minutes at low temperature in the solution medium, using microwave irradiation. Ferric acetylacetonate [Fe(acac)₃] and cobalt acetylacetonate [Co(acac)₂] in stoichiometric proportion (1:2) were used as the precursors and their solution in a suitable mixture of alcohols was irradiated for various durations and at various levels of incident power. The resulting samples were annealed under different conditions, and characterised by powder XRD, FTIR, XPS, SEM, TEM, and magnetic measurements. The as-prepared powder is found to have the spinel structure, with a crystallite size of ~9 nm. Depending on the annealing protocol, the annealed samples have crystallite sizes ranging from 9 nm to 30 nm. XPS analysis shows that the samples have the partially inverted spinel structure, with the degree of inversion ranging from 0.33 to 0.59. Magnetic measurements show that, at room temperature, the CoF powder samples are superparamagnetic, with strong magnetization at relatively low fields, making them suitable for application in the hyperthermia treatment of cancer. Low temperature measurements (30 K) show that the saturation magnetization of CoF powder can be as high as 83 emu/g and that of the CoF film is 403 emu/cc. The nanocrystalline CoF films are also superparamagnetic at room temperature, the saturation magnetization and coercivity increasing with annealing temperature. We have also investigated nanocrystalline CoF powder for its potential for energy storage. In a composite formed with carbon, CoF is found to be a promising electrode material for supercapacitors. The specific capacitance is found to depend on CoF crystallite size. Details of the magnetic and electrochemical measurements, its cytocompatibility, and the electrochemical characteristics of the powder/carbon composite as a function of the crystallite size of CoF will be reported. The results of similar investigations on CoF films will also be presented.

Graphite-doped hematite and magnetite nanoparticles systems (~50 nm) were prepared by high energy ball milling for processing times ranging from 2 to 12 hours. 57Fe Mossbauer spectroscopy has been used as a high resolution analytical tool to study their structure, magnetic properties, site preference and phase evolution. The spectra corresponding to the hematite milled samples exhibited line broadening and were analyzed by considering two sextets, indicating the incorporation of carbon atoms into the hematite lattice. A quadrupole-split doublet was added for the ball milling time of 12 hours, representing the contribution of ultrafine particles. The Mossbauer spectra of carbon-doped magnetite were resolved considering a sextet and a magnetic hyperfine field distribution, corresponding to the tetrahedral and octahedral sublattices of magnetite, respectively. The increase in the width of the distribution with milling time suggests that carbon atoms show preference for the octahedral sites. A quadrupole split doublet was incorporated in the fitting of the 12-hour milled sample. The recoilless fraction for all samples was determined using our previously developed dual absorber method. It was found that the recoilless fraction of the graphite-doped hematite nanoparticles decreases as function of ball milling time. The f factor of graphite-containing magnetite nanoparticles for the tetrahedral sites remains constant, while that of the octahedral sublattice decreases as function of ball milling time. These findings on the recoilless fraction further support the idea that carbon atoms exhibit preference for the octahedral sites of magnetite.
NSF-DMR-0854794 and NSF-DMR-1002627-1

Using Magnetic drug delivery enables targeting tumors deep in the body through the remote control of magnetic nanoparticles with external magnetic sources. There are two main advantages related to this technique: 1) it is a non-invasive approach towards treating cancer cells 2) it has been depicted by many researchers that this method enhances the concentration of drug in the tumor region. Effective concentration requires magnetic sources exhibiting very high magnetic fields and very strong field gradients. However, we demonstrate that such sources cause even 150 nm nanoparticles to form significant chains and aggregations. These aggregates can easily exceed the size of the interstitial tumor space and prevent particles from transcytosis and phagocytosis into the intended tumor cells.
In this work we offer a new scheme to concentrate and de-aggregate magnetic nanoparticles simultaneously at tumor sites in order to enable transcytosis and phagocytosis. This technique relies on dynamically tuning the direction (but not magnitude) of the field to put magnetic nanoparticles into repulsive configurations with neighboring particles driving them into disruption. In situ experiments that recreate porous tissue with a Teflon scaffolding show that penetration of the MNPs is enhanced by 2-fold with dynamic magnetic fields compared to static fields. Cell studies have also been done to study the effects of dynamic magnetic fields on biological systems.
In this work, we have simultaneously developed theoretical, numerical and experimental frameworks to study particle kinetics under dynamic magnetic fields. Experimentally we have investigated both computer-controlled solenoid setups with low gradients and robotically controlled permanent magnets. Visualization of nanoparticles was enabled with a customized dark-field setup that allowed collection and analysis of real-time behavior. Our numerical models include Brownian motion and magnetic models that account for mutual magnetization between neighboring particles.

The seamless integration of magnetic nanomaterials with cells and biological circuits is crucial for sensitive, specific and biocompatible applications in medical diagnosis and therapy. Combining tools and techniques from synthetic biology with material science, we have demonstrated in vivo biosynthesis of magnetic nanoparticles with tunable physical properties based on engineering of biomineralization proteins such as ferritins. Protein self-assembly based synthesis yields control over the size, shape and polydispersity of the inorganic nanoparticle products and naturally confers biocompatibility. To monitor and optimize in vivo bioinorganic synthesis, we developed a genetic biosensor that enables real-time fluorescent measurement and sorting of cells for intracellular iron uptake and sequestration. Genetic engineering of cellular transporters for accumulation of specific transition metals allows both increased production as well as doping of magnetic iron oxide particles by Co and Zn to vary coercivity. Furthermore, by targeted protein mutagenesis combined with directed evolution of random mutagenesis libraries, we discovered and characterized mutations that alter iron binding and nucleation, leading to significantly increased magnetic permeability that facilitates magnetic sorting and manipulation of the transgene expressing cells. Integrating the mutated genes into natural or synthetic genetic circuits has enabled the genetically-encoded nanoparticles to serve as reporters of biological activities analogous to the green fluorescent protein. However, with the much lower attenuation in tissues of magnetic field compared to visible light, chemical or inflammation induced biosynthesis of magnetic nanoparticles in gut bacteria generated image contrast via T2 weighted MRI, enabling non-invasive detection of disease and diverse compounds in deep tissues of animal models and humans with improved sensitivity. Furthermore, magnetic hyperthermia of the biosynthesized nanoparticles allows radio-frequency remote-control of biological circuits and activity in vivo via heat-sensitive protein and RNA constructs, leading to exciting novel applications in neuroscience and therapy.

The Molecular Imaging and Nanotechnology Laboratory at the University of Wisconsin - Madison (http://mi.wisc.edu/) is mainly focused on three areas: 1) development of multimodality molecular imaging agents; 2) nanotechnology and its biomedical applications; and 3) molecular therapy of cancer.
In this talk, I will present our recent work on molecular imaging and image-guided drug delivery in cancer with a variety of nanomaterials. The nanomaterials that will be discussed in this presentation include magnetic nanoparticles, magnetic nanocomposites, nano-graphene oxide, micelles, silica-based nanoparticles, among others. The primary imaging techniques used in these studies are positron emission tomography (PET), photoacoustic tomography (PAT), optical imaging, and magnetic resonance imaging (MRI). Three of the major molecular targets that we are investigating are CD105 (i.e. endoglin), VEGFR, and integrin α_vβ₃. A few representative side projects will also be presented, such as the facile synthesis of PET/MRI dual-modality agents via chelator-free radiolabeling.

In order to targeting deliver medicines to cancer cells, variety of nanoparticles have been applied as carriers for drugs and targeting molecules, and magnetic nanoparticles (MNP) is one of the most typical examples. As a widely used carrier in drug delivery system, MNP has mangy merits such as biocompatibility, low toxicity and hydroxyl group-rich surface. In additional, the well-known magnetism of MNP enable it to be employed as a contrast agent in magnetic resonance imaging. In this study, MNP with surface modification of targeting molecules and anticancer drugs was fabricated. MNP was first synthesized by FeCl₃ and FeCl₂ in the presence of ammonia solution at 70 °C with stirring, the size and the morphology of resultant nanoparticle was investigated by dynamic light scattering and electron microscopy respectively. The surface of MNP was then immobilized with a short peptide called epidermis growth factor fragment (EGFfr) at different MNP/EGFfr ratios, which has much lower molecular weight than whole EGF protein, and can target cancer cells with overexpressed epidermis growth factor receptor (EGFR) on the surface, via a Succinimidyl 3-(2-Pyridyldithio) Propionate (SPDP) linker. EGFfr-DOX-MNP with various MNP/EGFfr ratios was incubated with EGFR surface overexpressed A549 cell line and the uptake of EGFfr-MNP was evaluated using inductively coupled plasma optical emission spectrometry, by which means the MNP/EGFfr ratio can be optimized. Doxorubicin (DOX) was subsequently conjugated as a model drug with MNP through a pH sensitive 6-hydrazinonicotinate acetone hydrazone (SHNH) linker. When EGFfr-DOX-MNP was administrated and uptake by cancer cells, the low pH inside cancer cells induce the cleavage of SHNH and the release of DOX, resulting in cell death. The release rate of DOX was confirmed in vitro by incubating DOX-MNP in citrate buffer (pH 5.3) and measuring the absorbance of released DOX at 484 nm. In vitro cell uptake test was performed using A549 cell line, and CHO was chosen as a control because of the low expression level of EGFR. EGFfr-DOX-MNP and bare MNP was incubated with two cell lines, the uptake of nanoparticles by cells was observed by transmission electron microscopy and confocal laser scanning microscopy and the toxicity of nanoparticles was determined by MTT assay.

Graphene Quantum dots (GQDs) are proving to be an effective Imaging paraphernalia for the comprehension of morphological alterations in the cellular membrane due to high absorption coefficients and Quantum efficiency. Such Quantum dots can be used in drug/delivery vehicles, Biolabelling as well as in PCR. An upsurge of expanded interest in the field of Magnetic nanotechnology has led us to allow indepth exploitation of magnetic nanoparticles in nanomedicine. Encapsulating the core made up of magnetic nanoparticles by Gold nanoshell leads to the development of a proficient biocompatible and stabilized drug/delivery system under physiological conditions. Further creating a nanocomposite by allowing conglomeration of Au- Fe₃O₄ core-shell with GQDs
This modular design enables Au-Fe₃O₄-GQDs to perform multiple functions simultaneously, such as in multimodal imaging, drug delivery and real-time monitoring, as well as combined therapeutic approaches. The ability of MNPs to enhance proton relaxation of specific tissues and serve as MR imaging contrast agents is one of the most promising applications of nanomedicine. In the present work, Au-Fe₃O₄ nanoparticles are used as able cargo for the docking of anti-cancer drug such as Doxorubicin (DOX) using cysteamine as a linker for the attachment. The attachment could be monitored using UV-visible spectroscopy. The stability of Au-Fe₃O₄ nanoparticles was scrutinized by measuring the flocculation parameter which was found to be in the range of 0-0.65. Further, zeta potential measurements confirmed the pH of 7.4 at which maximum drug attachment can take place. The amalgamation of the drug along with activated folic acid as a navigational molecule is the critical phase for targeted drug delivery. Attachments were verified using FTIR and NMR which confirmed the formation of non-covalent interactions. The drug loading capacity of the Au-Fe₃O₄ was found to be 76%. Drug-release was studied using the AC magnetic field generator and was found to be temperature dependent phenomena. GQDs were found to be effective players in tracking the drug-delivery vehicle around the miscreant cell and inside them. Au-Fe₃O₄-GQD-FA-DOX complex was found to be comparatively non-toxic for normal cells and considerably toxic for Hep-2 cells due to hyperthermal properties of SPIONS and targeted-mechanism of folic acid.

The Magneto-impedance (MI) effect is a large change of the electrical impedance of soft magnetic materials to the flow of an ac current as a function of the external magnetic field. MI has been extensively studied in different soft magnetic materials, shapes and configurations and in a wide range of frequencies, and thin film MI structures are well suited for magnetic microsensors. In previous works we have systematically studied the influence of the preparation conditions and the structure on the properties of thin film permalloy-based multilayers. In this work we use an optimum combination of magnetic and non-magnetic layers that maximizes the MI performance. The MI multilayer structures exhibit a large sensitivity to low magnetic fields due to their high permeability, making them suitable to be used as magnetic biosensors whose performance competes with fluxgate magnetometers.
Devices were made from sputtered permalloy (Py) films which had soft magnetic behavior at thicknesses below 200 nm. Thicker (up to 1 micron) soft multilayer structures with high permeability were obtained by inserting thin (nanometer thick) Ti spacers between consecutive Py layers. Additionally, the MI performance was greatly enhanced in sandwich structures composed by a non-magnetic Cu layer between two magnetic multilayers of equal thickness. For fabrication simplicity we used an open flux configuration stack of [Py(100 nm)/Ti(6 nm)]₄ /Cu(400 nm)/ [Ti(6 nm)/Py(100 nm)]₄. Rectangular samples 10mm x 0.5mm were deposited by DC sputtering through shadow masks under a 250 Oe magnetic field oriented perpendicularly to the long side of the samples inducing a transverse anisotropy. A second series was prepared by photolithography using a lift-off procedure to achieve micro-patterned rectangular samples, 0.5 to 2 mm long and 10 to 140 µm wide.
Hysteresis was measured using the magneto-optical Kerr effect (MOKE). For magneto-impedance measurements the samples were inserted into a microstrip transmission line. Samples were characterized in a frequency range from 300 kHz up to 300 MHz, at fields up to 150 Oe. The impedance was extracted from the measurement of the reflection coefficient in a network analyzer as a function of the frequency and the applied magnetic field. The magneto-impedance ratio, calculated from the absolute value of the impedance Z, was MI = 100*(Z-Z_min)/Z_min = 350 % and the sensitivity, calculated as the field derivative of the MI ratio, was 300 %/Oe. The application of these devices for magnetic bead sending was investigated.

The clinical translation of Magnetic Particle Imaging (MPI), a new whole-body medical imaging technology with promise in vascular angiography, molecular imaging and cell tracking, depends critically on the nanoscale materials properties of the tracers. In fact, the structural, chemical, magnetic, and biological characteristics of the tracers need to be carefully optimized in vivo for best performance.
We describe the development of highly optimized nanoparticle tracers with magnetic properties tailored for the physics of MPI using a sound theoretical framework[1], an organic synthetic route producing magnetite cores in gram quantities[2], with controlled shape, narrow size-distribution and high phase purity[3]. We present details of their relaxation characteristics[4], size-dependent ferrohydrodynamic relaxometry[5] and subsequent phase-transfer without agglomeration in biologically relevant media, and functionalization for targeting, biocompatibility, adequate in vivo circulation[6] (tailorable between 4-120 minutes in mice models) and safe biodistribution (no uptake in the kidneys, critical for imaging patients with chronic kidney disease). In MPI phantom images, reconstructed in either real or Fourier space, these optimized tracers showed significant improvement compared to existing commercial particles (Resovist^®), in both normalized signal intensity (6x) and spatial resolution (50% better) approaching, clinically relevant, sub-mm at 6 T/m/mu;₀ field gradients. Further, their MPI signal is linear with concentration, with contributions mainly from Néel relaxation with some Brownian alignment³, making them suitable for molecular imaging[7]. Finally, we have established a flexible platform for functionalization the magnetic cores with PEG (to increase water solubility, enhance circulation time, and improve shelf life), dyes[8] (to turn them into multimodal -- MRI, MPI and NIRF -- contrast agents and to further enhance studies of their biodistribution with significant anatomical detail in rodent models) and ligands[9] (e.g. Lactoferrin with specific affinity for glioma cells) tailored for targeted molecular imaging.
These critical results, pave the way for improved clinical translation of MPI, as demonstrated in recent blood volume images[10] in rodents^,[11].
[1] Saqlain A. Shah et al, Phys. Rev. B (submitted)
[2] S.J. Kemp, et al , Proc. 5^th IWMPI (2015)
[3] Ryan Hufschmi et al,Nanoscale (accepted, in press), DOI: 10.1039/C5NR01651G
[4] C. Kuhlmann et al, IEEE Trans. Mag. 51, 6500504 (2015)
[5] Hamed Arami et alMedical Physics40, 71904 (2013)
[6] Amit P. Khandhar et al , IEEE Trans. Mag. 51, 5300304 (2015)
[7] R.M. Ferguson et al, IEEE Trans. Med. Imag. 34, 1077 (2015)
[8] Hamed Arami et al, Biomaterials52, 251 (2015)
[9] Asahi Tomitaka-Kami et al, Nanoscale (submitted)
[10] P. Goodwill et al, Proc. 5^th IWMPI (2015)
[11] This work was supported by NIH/NIBIB grants 1RO1EB013689-01, 1R41EB013520-01 & 2R42EB013520-02A1

Magnetotactic bacteria produce chains of magnetosomes, the intracellular nanometer-sized magnetic crystals surrounded by a thin phospholipid bilayer membrane. Magnetosomes exhibit nearly perfect crystal structures with narrow size distribution and consistent species-specific morphologies, leading to desirable magnetic properties. As a result, the magnetite biomineralization in these microrganisms is of fundamental interest to diverse disciplines, from biotechnology to astrobiology [1]. Current studies point to a number of steps involved in magnetosome growth, including cellular uptake of soluble iron, its complexation with membrane proteins, and nucleation and growth of a mature magnetosome. However, the molecular mechanism of biomineralization in magnetotactic bacteria and the magnetosome nucleation and growth process remains unclear. Recently, we demonstrated a correlative electron and fluorescence microscopy technique for imaging live magnetotactic bacteria in liquid with nanometer resolution using an environmental fluid cell, and identified imaging conditions under which the microorganisms did not sustain observable electron beam damage [2].
Current effort is focused on probing the magnetosome magnetite biomineralization both in vivo and in vitro by using the combination of correlative STEM-FM imaging, electron diffraction, and analytical spectroscopy. While the crystal structure of magnetosome magnetite is well-established, far less is known about the chemical environment of the biomineral at the early stages of magnetosome formation. To this end, we employed the combination of electron diffraction and EELS analyses to probe the crystallinity and chemical bonding in the nascent magnetosome particles. Newly formed magnetosome particles are mostly amorphous, whereas the fully grown magnetosomes are unambiguously indexed to magnetite. We have identified the narrow “transition range” corresponding to the onset of crystal lattice formation. We utilized the peak fitting analysis of EEL spectra to monitor the evolution of chemical bonding in magnetosomes and correlated these findings with the emergence of crystalline lattice.
[1] Prozorov, T.; Bazylinski, D. A.; Mallapragada, S.K.; Prozorov, R. “Novel Magnetic Nanomaterials Inspired by Magnetotactic Bacteria: Topical Review” Mater. Sci. Eng. R., 2013, 173, 133-172.
[2] Woehl, T. J., Kashyap, S.; Perez-Gonzalez, T.; Faivre, D.; Trubytsyn, D. ; Bazylinski, A. D.; Prozorov, T. “Correlative Electron and Fluorescence Microscopy of Magnetotactic Bacteria in Liquid: Toward In Vivo Imaging” 2014, Sci. Rep., 4, 6854.

The treatment of early-stage breast cancer typically involves mastectomy or lumpectomy followed by radiation therapy to remove any residual cancer cells. Although mastectomy leaves relatively less residual cells, it is an aggressive form of treatment for early-stage breast cancer. Therefore, treatment modalities that could enhance the use of lumpectomy are needed. In this work, a combination of experiments and models was used to explore the use of magnetic nanoparticle (MNP)-filled PDMS nanocomposites for post-operative treatment of breast cancer. First, the structural, magnetic and thermometric properties of magnetic nanoparticle (MNP)-filled PDMS nanocomposites were studied as a function of MNP (γ-Fe₂O₃) weight fraction. Then, in an effort to investigate the in-vivo thermal profiles and doses, a 3D finite element method (FEM) model was used to simulate the heating of breast tissue under alternating magnetic field (AMF) parameters safe for human use. The properties of the nanocomposites were shown to be controlled by the properties and weight fraction of MNPs. Furthermore, thermoseeds were shown to have the potential to achieve in-vivo hyperthermic or ablative temperature levels. The results show that, by controlling the amount of MNPs, this simple multifunctional nanocomposite system has the potential to achieve lesion sizes required to eliminate residual cells under AMF parameters that are safe for human use.

The magnetic properties of rare-earth materials were the subject of intensive studies in the sixties years. With the success of modern crystal growth techniques to produce rare-earth multilayers, the interest in this subject is currently undergoing a fast resurgence, with exciting new perspectives for the future [1]. On the other hand, magnetic ordering in the heavy rare-earth lanthanides is mediated by the RKKY interaction in which the polarization of conduction electron yields an indirect exchange between localized 4f moments on neighboring lattice sites. The interplay between this long-range interaction and anisotropic and magneto-crystalline effects results in complex magnetic ordering and the possibility of a variety of magnetic structures. One of the most recent purposes is the use of these materials in solid-state rare-earth-ion-doped systems, which justifies their status as very strong candidate to energy storage in a long-lived quantum memory system [2]. The present work intends to contribute to the study of the magnetic phases of rare-earth thin films, aiming further applications.
In this work we investigate theoretically a c-axis holmium thin film, consisting of a stacking of atomic layers with equivalent spins, infinitely extended in the x y minus; directions. We consider that the spins in each monolayer are exchange coupled with the spins in the first and second neighbor monolayers. The anisotropy is uniform throughout the film and the near-surface spins have reduced exchange energy. To study the magnetic phases as functions of the applied magnetic field, we use a self-consistent local field model which incorporates the surface modifications in the exchange field and the thermal average values (n> ; n=1 hellip; N ) and the orientation of the spins in each layer (n> ; n=1 hellip; N ). Our main purpose is to study the magnetic phases of very thin Ho films in the temperature interval between 20 K and 132 K. Specifically, we investigate the influence of the surface and thickness of a thin film, associated with the existing competition between the energies of exchange and magneto-crystalline anisotropy, when in the presence of an external magnetic field and temperature. The present study shows the strong influence that the surface and thickness of a thin film associated with the existing competition between the energies of exchange and magnetocrystalline anisotropy, exerts on the magnetic order of these systems, when in the presence of an external magnetic field and temperature. The slab size, surface effects and magnetic field due to spin ordering impact significantly the magnetic phase diagram.
[1] B. Hjörvarsson, R. Pentcheva, Springer Tracts in Modern Physics 227 (2007).
[2] N. Timoney, I. Usmani, P. Jobez, M. Afzelius, N. Gisin, Phys. Rev. A 88 (2013) 022324.

The development of next-generation permanent magnets for energy conversion requires realization of novel materials with lower cost and reduced environmental impact. To move beyond rare-earth-based magnetic materials currently used, research interest has shifted to compounds comprised of earth-abundant elements. With high uniaxial magnetocrystalline anisotropy and large saturation magnetization, the low cost and good availability of the constituent elements make L1₀ FeNi, with a tetragonal crystal structure, ideal for bulk permanent magnet construction. However, L1₀ phase formation in this system is highly kinetically limited and thus it is only found naturally in meteorites that have cooled over billions of years to produce this phase. To enable laboratory-based investigation of factors that impact formation of tetragonal FeNi, the FeNi₃ compound is employed as a model system. FeNi₃ can adopt the chemically-ordered cubic L1₂ structure that features iron and nickel atoms in specific lattice positions to form a superstructure, much like that found in the L1₀ FeNi, but is easily synthesized in the lab.
To furnish insight into effect of alloying elements on the formation of L1₂ superstructure, alloys of FeNi₃, (FeNi₃)_0.98Mn_0.02, and (FeNi₃)_0.98Cu_0.02 have been synthesized by the arc-melting technique, followed by annealing for 336 h at 470 °C. Coupled thermal and magnetic characterizations show enhancement in the formation of L1₂ phase with Mn addition and reduction with Cu addition to FeNi₃.

Nanostructured permanent magnetic materials have drawn considerable attention in recent years due to their various unusual scientific and technological applications, inc1uding magnetic recording devices, Micro-Electro Mechanical Systems (MEMS), and the so-called next generation hard/soft phase nanocomposite permanent magnets. Binary Mn-Al compound, as a quite useful ferromagnetic intermetallic material with a long history, has remarkable properties of the low-temperature phase, the quenched high-temperature phase, and the new metastable alloy phase.
The low-temperature tau;-phase of MnAl has attracted much interest as a potential rare-earth-free permanent magnet material because of its high uniaxial magnetocrystalline anisotropy at room temperature [1]. Magnetic properties of the Mn-Al alloys are associated with the existence of a tau;-ferromagnetic phase having an ordered tetragonal crystal structure. This phase is magnetic uniaxial, it has a high magnetic anisotropy and relatively low saturation. Ferromagnetic phase is unstable. During the formation tau;-phase and its subsequent decay to equilibrium phases have seen a dramatic change in the magnetic properties, the behavior of which has not been established definitively. Nature of high coercive force cast alloy is also far from clear. Also the details associated with the tau;-phase are not clarified [2-4].
In this work we report about the result of investigation of the magnetic properties Mn-Al cold rolled ribbons. The obtained results were compared with the magnetic properties measured on samples of polycrystalline and monocrystalline Mn-Al alloys.
Authors appreciate the RF President MD-770.2014.2 grants for financing this work.
[1]. J.H. Park, Y.K. Hong, S. Bae, J.J. Lee, J. Jalli, G.S. Abo, N. Neveu, S.G. Kim, C.J. Choi, and J.G. Lee: J. Appl. Phys., 2010, vol. 107, p. 09A731.
[2]. D.P. Hoydick, E.J. Palmiere, and W.A. Soffa: J. Appl. Phys., 1997, vol. 81, pp. 5624-26.
[3]. K. Kamino, T. Kawaguchi, and M. Nagakura: IEEE Trans. Magn., 1966, vol. 2, pp. 506-10.
[4]. Z.C. Yan, Y. Huang, Y. Zhang, G.C. Hadjipanayis, W. Soffa and D. Weller: Scripta Mater., 2005, vol. 53, pp. 463-68.

Magnetic materials have been investigated due to their potential application in different technological devices such as computer read/write heads, magnetic sensors, electromagnetic shielding, permanent magnets, micro electrical mechanical system (MEMS). The changing of the morphological and microstructural properties can produce significant change in different properties such as mechanical, electrical, magnetic and optical ones. Electrodeposition is an interesting method to synthesize nanostructured materials because it can, in a controlled form, modify the morphology, microstructure and composition of the prepared samples. In this work, the effect of deposition variables on the composition, structure and surface morphology were studied to explain the magnetic properties of the alloys. To decrease the number of experiments to be carried out, it was a 2³ factorial design to perform the electrodeposition of NiFeCu alloys. The studied parameters were the deposition potential, deposition time and temperature of the electrolytic solution. A typical three-electrode cell was used, with a platinum foil as counter-electrode and a saturated electrode Ag/AgCl as reference electrode. X-ray diffraction (XRD) data analysed by Rietveld refinement have shown that the NiFeCu alloy exhibit face-centred cubic (FCC) structure with preferred orientation in the (111) direction. In addition, the change in mean crystallite size may be related temperature variations and with the iron content in the alloys. Using FEG-SEM microscopy, it is observed that the morphologies of the alloys are modified by the experimental conditions. The magnetic properties were investigated using SQUID magnetometer measurements, in which it was observed that the increasing of the saturation magnetization (M_S) can be related to de modification of the NiFeCu alloy composition. Besides, the NiFeCu films display weak hysteresis behavior and exhibit a coercive (H_C) from 29-33 Oe. Furthermore, the strain could have an influence in the anisotropy of almost all magnetic materials by magnetostriction. In conclusion, it was demonstrated that the electrodeposition can lead to the preparation of different materials with controlled properties.
Acknowledgement:
CNPq, CAPES and FAPESP (2012/22934-2)

We realized thin layers of magnetite, zinc oxide and titanium dioxide, by developing a
new technique based on the effervescence bio compatible materials to produce uniform thin films on the whole surface. Optical characterization was carried out to study the impact of these thin layers on the absorption spectrum of the glass. This relatively inexpensive technique is developed to achieve anti reflective coatings for optical glass.

High-performance hard magnetic materials can store high magnetic energy density and have a vast number of technological applications. Nowadays, the best magnetic materials meeting technical specifications are based on neodymium iron boron magnet (Nd2Fe14B). However its low Curie temperature (Tc = 585 K) limit its use only in low temperature (below 500K). The aim of this project is to prepare nano-scale magnets based on samarium cobalt (SmCo5, Tc = 1020 K) or manganese bismuth (MnBi, Tc = 771 K)) for high temperature applications. To improve their energy product, nanocomposites which combine hard (SmCo5 or MnBi) and soft (Co, Fe, or FeCo) magnets together with both a large coercivity and a large moment will also be prepared and studied.

In this work we report the results of investigation of magnetocaloric effect in Gd_100minus;xC_x (x=0..10) cold rolled ribbons. The principal idea of this work is to obtain information about the influence of severe plastic deformation (SPD) on magnetocaloric properties. Such kind of alloys has direct application to the new technology of magnetic cooling. Since the discovery in 1997 of the laquo;giant magnetocaloric effectraquo; [1] the development of magnetic refrigeration has been growing exponentially and many alloys have been designed as a possible magnetocaloric materials. Nevertheless, Gd and Gd-based alloys are still one of the best compounds for such technology ever done.
Today there is a lack of information about the influence of SPD on magnetic and magnetocaloric properties, but as it is shown in some papers plastic deformation dramatically affect on the magnetic and other physical properties, for instance, see [2]. According to degree of plastic deformation magnetic, structural or thermodynamic properties of the media could be modified and that&’s the point not only of academic interest, but also of practical application.
As it shown in as-cast low carbon Gd_100minus;xC_x alloys magnetocaloric effect do not decrease significantly, also we observe increasing Curie temperature. After cold rolling treatment magnetocaloric effect decrease correspondingly to applied deformation. This effect goes from the defects of structure, which are induced during cold rolling and this result in a random magnetic anisotropy in the SPD material. Special high-temperature heat treatment can restore magnetocaloric properties of the cold rolled ribbons back to the bulk ones [3]. The heat treatment regimes are directly connected with the degree of deformation.
Authors appreciate the RF President MD-770.2014.2 grants for financing this work.
[1] K. A. Jr. Gschneidner, V. K. Pecharsky, Int. J. Refrig., 31 (2008) 945
[2] S. V. Taskaev, M. D. Kuz`min, K. P. Skokov, D. Yu. Karpenkov, A. P. Pellenen, V. D. Buchelnikov and O. Gutfleisch, JMMM,331 (2013) 33.
[3] S. Taskaev, K. Skokov, V. Khovaylo, V. Buchelnikov, D. Karpenkov, A. Pellenen, M. Ulyanov, D. Bataev, A. Usenko, M. Lyange, and O. Gutfleisch, J. Appl. Phys,117 (2015) 123914.

Magnetocaloric effect (MCE) is an isothermal entropy change or an adiabatic temperature change of a magnetic material upon application of a magnetic field. Magnetic cooling technique based on MCE of materials is now considered as a serious alternative for conventional refrigeration. Rare-earth metal Gd is a popular second order transition magnetic refrigerant for the room temperature magnetic refrigerator. The cooling efficiency in magnetic refrigerators working with Gd was shown to reach 60% of the theoretical limit compared to only about 40% in the best vapor-compression refrigerators. For practical applications near room-temperature, it is necessary to search for magnetic refrigerants that possess MCE (ΔT_AD or ΔS_M) as good as Gd, and have a Curie temperature (T_C) near room-temperature(~298±30 K). In order to alter T_C (to increase the working temperature range) and increase the maximum magnetic entropy change (-ΔS_M)_max, many binary Gd-based alloys have been studied.
In the present work we report the magnetic and magnetocaloric properties of the series of intermetallic alloys Gd_100minus;xIn_x with the concentration In of 6 at.% treated with the help of cold rolling technique. Such technique is very convenient for designing new functional materials. For instance, one of the possible ways for designing materials for magnetic refrigeration [1] is tightly connected with preparation very thin (up to several micrometers) foils with high magnetocaloric effect and good mechanical properties. But as it is shown in our previous works [2-4], severe plastic deformation leads to significant depression of the magnetocaloric effect in cold rolled Gd foils.
As it shown in these research, excess of In atoms negatively affect on the magnetocaloric effect, moreover additional plastic deformation decrease magnetization and this in its turn decrease magnetocaloric effect additionally.
Authors appreciate the RF President MD-770.2014.2 grants for financing this work.
[1] K. A. Jr. Gschneidner, V. K. Pecharsky, Int. J. Refrig., 31 (2008) 945
[2] S. V. Taskaev, M. D. Kuz`min, K. P. Skokov, D. Yu. Karpenkov, A. P. Pellenen, V. D. Buchelnikov and O. Gutfleisch, JMMM,331 (2013) 33.
[3] S. Taskaev, K. Skokov, V. Khovaylo, V. Buchelnikov, D. Karpenkov, A. Pellenen, M. Ulyanov, D. Bataev, A. Usenko, M. Lyange, and O. Gutfleisch, J. Appl. Phys,117 (2015) 123914.
[4] S. Taskaev, K. Skokov, D. Karpenkov, V. Khovaylo, V. Buchelnikov, D. Zherebtsov, M. Ulyanov, D. Bataev, M. Drobosyuk, A. Pellenen, APPA,127 (2015) 641-643.

Iron chalcogenides, such as FeTe and its solid solutions with other transition metals have been targeted for their interesting magnetic properties [1], which become one of the potencial materials for recording media, superconductivity, and permanent magnets. To date, much effort have been made to prepare transition metal chalcogenide nanocrystallites through elemental reaction in vacuum at high temperatures or mechanical alloying [2,3]. These processes are usually complicated and time-consuming and their products are bulk materials with large grain sizes. Recently, Fe₃Se₄ nanostructures with giant coercivity of 4 tesla at 10 K were reported by solution phase techniques [4]. FeTe₂ nanocrystallites with higher coercivity at room temperature were also obtained by a hydrothermal co-reduction method [5]. However, these particles do not have well controlled morphologies and are difficult to disperse in a solution. In this work, we report for the first time FeTe₂ and Cr-doped FeTe₂ nanoparticles with uniform sizes that are well dispersed in organic solvents. Both the morphology and magnetic properties can be controlled by Cr doping.
Iron(III) acetylacetonate [Fe(acac)3], chromium(III) acetylacetonate [Cr(acac)3], and Te power were chosed as precursors to synthesize FeTe₂ and Fe_1-xCr_xTe₂ nanoparticles by high-temperature organic solution reaction. The crystal structure, morphology, magnetic property were identified by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer(VSM).
It is found that FeTe₂ with ferromagnetic behavior (Hc=190 Oe, Ms=0.03 emu/g) is obtained for Fe:Te = 1:2. When Cr is doping into FeTe₂, the Ms of (Fe_1-xCr_x)Te₂ increases first, and then decreases with increasing Cr concentration. Fe_0.85Cr_0.15Te₂ shows the maximum Ms of about 7.65 emu/g, which is 200 times larger than that of FeTe₂. However, there is no sgnificant defference for their coercivities. The ferromagnetic control of (Fe_1-xCr_x)Te₂ is due to the superexchange mechanism similar to that of FeSe_x. The dispered nanoparticles with grain size smaller than 10 nm are observed for both FeTe₂ and Fe_1-xCr_xTe₂. FeTe₂ with Cr doping exhibits a larger size than that of FeTe₂. Therefore, Cr doping plays an important role in controlling magnetic properties and nanostructures.
References:
[1] Wu, X.J.; Zhang, Z.Z.; Zhang, J.Y.; et al. Thin Solid Films 2008 516, 6116.
[2] Feng, Q.J.; Shen, D.Z.; Zhang, J.Y.; et al. Appl. Phys. Lett. 2006, 88, 012505.
[3] Mizuguchi, Y.; Tomioka, F.; Tsuda, S.; et al. Appl. Phys. Lett. 2008, 93, 152505.
[4] Zhang, H.W.; Long, G.; Li, D.; et al. Chem. Mater. 2011, 23, 3769.
[5] Liu, A.P.; Chen, X.Y.; Zhang, Z.J.; et al. Solid State Commun. 2006, 138, 538.

Synthesis of magnetic metallic nanoparticles has been attracting considerable interest for medical applications such as cancer detection/therapy, drug delivery/targeting, magnetic resonance imaging contrast agents and hyperthermia. There is an increasing possibility of localizing magnetic metallic nanoparticles in cancer tissues since an external static magnetic field can fix and a gradient field can move them towards heat-sensitive tumor cells. However, instabilities of magnetic metallic nanoparticles such as oxidation, dissolution in acids and ease of agglomeration prevent their usage in related applications. Encapsulating a protective layer on these nanoparticles is one good solution to eliminate such limitations. It should be useful for instance to combine the biocompatibility and chemical inertness of carbon with the magnetic performance of magnetic nanoparticles.
This study reports on the formation, microstructure and room-temperature magnetic properties of graphite-encapsulated Fe nanoparticles prepared by a low-pressure chemical vapor deposition (LP-CVD) method. Fe nanoparticles were synthesized by the reduction of iron(III)nitratenanohydrate (Fe(NO₃)₃.9H₂O) which was impregnated into fumed silica after dispersing in ethanol, sonicating and drying treatments. Simultaneously, the graphitization was carried out in a horizontal tube furnace under a CH₄/H₂ atmosphere at 900°C. The effects of reaction duration (from 15 min to 1 h), CH₄/H₂ gas flow rate (from 80 to 500 ml/min) and cooling conditions (H₂ or CH₄/H₂) on the formation and microstructure of the products were examined. An additional purification step was conducted on the samples to leach out the SiO₂ contamination. Leaching in HF solution (2 % concentration), centrifugation (at 4500 rpm for 1 h) and washing yielded pure graphite-encapsulated Fe nanoparticles and they were characterized using high resolution transmission electron microscopy (HR-TEM) and alternating gradient magnetometry (AGM). The results show that soft-ferromagnetic Fe nanoparticles having a size of 8 nm and a graphite-encapsulation of trilayers could be obtained with a coercivity value of ~10 Oe.

Electrospinning is a unique method for producing micro and nano sized polymeric fibers consisting of high surface area, porosity and flexibility. It can further be utilized for producing nano-patterns in applications such as biosensors, magnetic recording and bioelectronics. Magnetite (Fe₃O₄) from the spinel group is the most magnetic natural mineral found on earth and it has been successfully used as a catalyst for the growth of carbon nanotubes (CNTs). Some of the other proposed applications of magnetite are in the preservation of long term memory, as an arsenic sorbent and also in hyperthermia for targeting tumors. In each of these applications, it is found that smaller the size of the magnetite crystals, better the efficiency. Here we come up with a novel use of electrospinning in creating nano-patterns of magnetite crystals (approx. 25nm) dispersed separately in acetic acid and Tris-HCL over an aluminum substrate fixed on a rotating disc collector spinning at 1500rpm. The nano-patterns obtained are for distances (between the needle and collector) of 11cm, 13cm, 15cm, 17cm, 19cm, 21cm and 23cm. Each electrospinning trial was performed for 2 hours for the respective distance and it was found that distances between 15cm and 19cm are the optimum distances at which largely evenly distributed individual magnetite crystals can be obtained. It was also found that distances play a significant role as they vary the electric field per unit distance and in turn produce self-assembled magnetite films, especially at distances below 15cm, which was confirmed through atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX) analysis. Effect of concentration and flow-rate to fine-tune the nano-patterns is underway and further we plan to experiment with a consistent nano-patterned magnetite substrate for chirality controlled growth of carbon nanotubes for applications especially in bioelectronics.

Mn-Ga alloys have shown promising hard magnetic properties, even though these alloys contain no rare-earth metals. However, much work is needed before Mn-Ga alloys are able to replace rare-earth magnets. One of the challenges is to enhance the remanence. One technique to improve this property is applying a magnetic field during the heat treatment process. Magnetic annealing creates a preferred domain orientation in the demagnetized state with the direction of magnetization in each domain parallel to the axis of the annealing field. This results in an increased anisotropy and remanence. Bulk samples of Mn-Ga, Mn-Fe-Ga and Mn-(FeB)-Ga alloys were made by mechanically alloying in order to create nanostructured composite, followed by heat treatments in the presence of a 31 T magnetic field. The heat treatment temperatures were kept low in order to keep the refined microstructure. All the alloys exhibit hard magnetic properties at room temperature with large coercivity. This work reports findings of magnetic field annealed Mn-Ga-X-Y bulk composites that exhibit high coercivities up to 19.4 kOe and increased remanence of 60% over the binary system, achieving values up to 6.9 emu/g. This is the highest coercivity reported in bulk Mn-Ga samples.

Typical magnetic nanoparticles do not have strong resonant optical scattering properties such as by plasmonic effects, particularly in the useful visible range. If ferromagnetism and plasmonics could co-exist in the nanoparticles it could lead to new as well as better functionalities, such as from the combination of traditional localized surface plasmon resonance (LSPR) sensing with contributions from magnetic effects. Here we discuss our recent discovery of ferroplasmons (ACS Nano, v8, p9790, 2014)) which are strong plasmonic resonances in the visible range in Cobalt (Co) and iron-Co (FeCo) ferromagnetic nanoparticles when in contact with silver (Ag) in the form of bimetallic nanoparticles. These bimetallic systems show many other interesting behaviors, including the suppression of Ag oxidation through a galvanic effect, enhanced LSPR sensitivity over that of pure Ag particles, and a strong magneto-optical Kerr effect. We will also discuss the synthesis of these bimetallic particles and their magnetic, plasmonic and magneto-optical properties in the context of symbiotic effects between the ferromagnetic and noble metal. The strong resonant interaction of light within the nanometer sized ferromagnetic particles also opens out a potential new route to plasmonically-assisted magnetic recording.
This work was primarily supported by an ARO grant W911NF-13-1-0428, and partly supported by grants from the NSF (CMMI CMMI-0855949 and CBET-1349507). The authors also thank the Joint Institute of Advanced Materials (JIAM) at University of Tennessee-Knoxville (UTK) and grant CNMS2013-284 at the Center for Nanophase Materials Science, which is sponsored at ORNL by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

Nanoparticle system xEu2O3-(1-x)alpha-Fe2O3 with molar concentration x = 0.1, 0.3, 0.5, and 0.7 was successfully synthesized by high energy ball milling of Eu2O3 and alpha-Fe2O3 mixtures for 0-12 hours of processing time. The study explores the formation of magnetic ceramic nanostructures, which is of crucial importance to catalysis, gas sensing and energy-related applications. Complementary techniques of investigation, such as X-ray powder diffraction (XRD), 57Fe and 151Eu Mossbauer spectroscopy as well as thermal analysis by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were used to study the structural, thermal and magnetic properties of xEu2O3-(1-x)alpha-Fe2O3 nanoparticle system as function of molarity and milling time. Rietveld refinement of the XRD patterns yielded the values of the lattice parameters and particle size as function of composition and ball processing times and indicated the formation of a single phase, the EuFeO3 perovskite for large x values and long milling times. The 57Fe Mossbauer studies showed that the spectrum of the ball milled nanoparticles developed from a sextet for hematite to sextets and a doublet upon duration of the mechanochemical activation with europium oxide. The 151Eu Mossbauer investigations showed that the isomer shift decreased with increasing milling time for all molar concentrations employed. These results correlate well with the DSC/TGA analysis, which showed the consumption of the precursors, hematite and europium oxide, and the formation of EuFeO3 perovskite in the system of mixed-oxide nanoparticles.

In recent years the synthesis of nanocrystals has been pursued intensively not only because of fundamental scientific interest, but also in view of technological applications. The synthesis of uniform-sized nanocrystals is of key importance, because their properties depend critically on size and shape. Although remarkable advances have been made in the synthesis of uniform nanocrystals, our understanding of their formation mechanism is limited.
We have developed facile methods to fabricate inorganic Janus particles (e.g. Au@MnO and Au@Fe₃O₄ heterodimers) by a seed-mediated nucleation and growth technique with precise control over morphology and domain sizes, as demonstrated by transmission electron microscopy and dynamic light scattering. High uniform particles were obtained for all heterodimer compositions, which allowed a comparison of the individual heterodimer systems regarding their composition and properties. The intrinsic hetero-epitaxial linkage enabled interfacial interaction of the individual components, which was reflected by modulation of the optical, magnetic, and structural characteristics. Pronounced differences between Au@MnO and Au@Fe₃O₄ were observed regarding the synthesis and the properties caused by the variation of the electronic structure of the metal oxides.
Besides Janus particles size- and shape controlled assemblies from several nanoscale building blocks are emerging as new types of particles. The seed-mediated synthesis can be extended Ni@Fe₂O₃ superparticles containing Ni cores densely covered with highly oriented γ-Fe₂O₃ nanorods (NRs) by controlled thermal decomposition of nickel acetate (Ni(ac)₂) and Fe(CO)₅. Automated diffraction tomography (ADT) of the Ni-Fe₂O₃ interface in combination with Mössbauer spectroscopy of the superparticles revealed that the selective and oriented growth of the γ-Fe₂O₃ nanorods on the Ni core is facilitated through the formation of Ni_1-xFe_x alloy and Ni-doped iron oxide “buffer layers” that reduce strain at the Ni-Fe₂O₃ interface. The reaction conditions can be fine-tuned to synthesize Janus-type Ni@Fe₂O₃ heterodimers and core-shell particles besides Ni@Fe₂O₃ superparticles in a highly controlled manner. The work provides a general approach to a new type of magnetic nanocomposites with complex but well-defined mesoscopic architectures through “beaker epitaxy” of nano-objects.

We have developed a unique mechanism for controlling the size of magnetic nanoparticles based on reversible magnetic agglomeration. In this mechanism, iron particles will nucleate and then grow in solution with their magnetic moment increasing as a function of particle size. At a certain critical size, the magnetic interactions between particles become strong enough to overcome the steric repulsion provided by the stabilizing ligand on the nanoparticle surface, and particles begin to magnetically agglomerate and precipitate out of solution. When this precipitation of particles occurs, they cease to further react in solution. By introducing more steric bulk into the 3-position of a ligand, 2,4-pentanedione, we can control the maximum size the particles can reach before magnetic agglomeration occurs. Because the blocking temperature, susceptibility, and saturation magnetization all vary as a function of particle size, displaying control over size allows the tailoring of the magnetic particles to a given application. With this method, zero-valent iron particles with sizes ranging from 6 nm to 20 nm were reproducibly synthesized.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Iron sulfide nanomaterials play a role in materials science like solar cells, biological and other applications. The crystal structure and phase transformations of iron sulfide compounds are complex. Reported in this work is the synthesis of iron sulfide nanoparticles by solvothermal and pyrolysis methods. Piperidine (1) and tetrahydroquinoline (2) dithiocarbamate complexes of iron (III) were used as single source precursors. Only greigite phase (Fe₃S₄) was obtained when solvothermal method was used during the synthesis. Pyrolysis method gave pyrrhotite phase and a mixture of pyrite (FeS₂) and pyrrhotite phases when complex (1) and (2) were used, respectively. In complex (2), pyrite (FeS₂) surfaced as dominant phase at reaction temperature of 350 ^oC while at 450 ^oC, pyrrhotite phase was dominant. The iron sulfide nanoparticles were further characterized by Raman and NIR-UV visible spectrophometers to investigate the optical properties. Morphology and sizes were studied by transmission and scanning electron microscopy. Furthermore, we studied the electro-magnetic properties of the as-synthesized iron sulfide nanoparticles by using cyclic voltammetry and magnetic sample vibrator. The samples were also studied for their catalytic application using Rhodamine B dye under the influence of UV-lamp and halogen light.

Nanomaterials have triggered a lot of attention as potential triggers for a technological breakthrough in Energy Storage Devices and specifically Li-ion batteries. Herein, we report the original synthesis of well-defined silicon/iron oxide nanoberries and its application as anode materials for Li-ion batteries. This model compound is based on earth abundant elements and allows for a full investigation of the electrochemical reactions through its iron oxide magnetic phase. The elaboration of silicon with iron oxide grown on its surface has been achieved by reacting an organometallic precursor Fe(CO)₅ with Si nanopowder and subsequent slow oxidation step in air yields hollow γ-Fe₂O₃ on the Si surface. This specific morphology results in an enhancement of the specific capacity from 2000 mAh/g_Si up to 2600 mAh/g_Si. Such a high specific capacity is achieved only for hollow γ-Fe₂O₃ and demonstrates a novel approach toward the modification of electrode materials with an earth abundant transition metal like iron. This result further emphasizes the need for precisely designed nanoparticles in achieving significant progress in energy storage.
Gal Grinbom et al, Chem. Mater., 2015, 27 (7), pp 2703-2710

Theranostics, combination of therapy and diagnostics, still cannot profit from nanoparticles&’ clinical use mostly due to the complex and often non-reproducible synthesis methods. Additional problems are the use of toxic molecules in the preparation, or the inability of available nanoparticles to simultaneously fulfill all the physicochemical and biomedical requirements. Among all the nanoparticle types, one of the most studied are iron oxide, although mostly for diagnostics by MRI, because their heating power is not yet sufficient to be used for hyperthermia treatment.
Here, we report the synthesis and characterization of iron oxide based nanoparticles (including iron oxide itself and doped by nontoxic metal ions) by a novel and facile aqueous synthesis route that gives us nanoparticle size tunability without the use of organic solvents and/or toxic molecules. By tuning particle size, crystallinity and magnetic properties, we obtained a specific loss power (SLP) value of up to 850W/g(Fe2O3). More precisely, after normalizing the SLP with the field and frequency, we obtained intrinsic SLP (ILP) values of up to 3.4nHm²kg^-1 (what is the highest reported value for single core iron oxide nanoparticles) at field intensities (H) and frequencies (f) close to the values accepted for clinical applications (Hf < 485 kHzkA/m). Our nanoparticles are not only suitable for the treatment but also show increased efficiency for diagnostics as MRI contrast agent with the highest so far reported both relaxivity r₂ of up to 925 s^-1middot;mM^-1 and relaxivities ratio r₂/r₁ of up to 195.

Magnetic nanoparticles, with many unique features, such as high monodispersity, homogeneous single crystallinity and satisfying stability, have been actively applied for rapid magnetic separation, magnetic resonance imaging (MRI) contrast enhancement, targeted drug/gene delivery, magnetic immunoassay, hyperthermia cancer treatment, etc. For biological and medical uses, water solubility and colloidal stability are prerequisites for MNPs, especially those synthesized via thermal decomposition method. To improve their performance and increase their functions for further biomedical applications, proper surface functionalization are needed. Here we will first briefly discuss how different size and shaped magnetic nanoparticles are made, then focus on the discussion of various surface coating strategies applied to transfer well-defined magnetic nanoparticles from organic solvent to water solution and protect them from aggregation and opsonization. Numerous surface functionalization strategies utilized to improve their performance in physiological environment, modify their biodistribution and make them multifunctional will also be described.

Magnetic nanoparticles of regular shape and uniform size, such as magnetite (Fe₃O₄), are highly desirable in biomedical and technological applications. The magnetic behavior of magnetite nanoparticles is primarily determined by their size, shape, purity and crystal structures. Tailored magnetic properties of magnetite nanoparticles to meet specific requirements will greatly expand the spectrum of applications. Many efforts have been devoted to studying and regulating the size, shape and magnetic properties of magnetite nanoparticles. Impurity doping in magnetite introduces preferred magnetic orientation and affects the magnetic properties. Meanwhile, impurity doping plays a crucial role on nucleation and growth of nanocrystals and it is successfully used to control size of upconversion nanocrystals. Here we investigated gadolinium (Gd) doping to influence growth process as well as magnetic properties of magnetite nanocrystals via a co-precipitation method under mild aqueous conditions. Gd doping was found to affect the growth process leading to synthesis of controllable particle sizes under the conditions tested (0-10 at. % Gd³⁺). Typically, 5 at. % Gd-doped magnetite nanoparticles were found to have crystal sizes doubled compared to undoped ones. The presence of Gd³⁺ ions led to enhancement of crystal growth presumably through a non-classical crystal nucleation theory. Our results showed that Gd-doped nanoparticles retained the magnetite crystal structure, with Gd³⁺ randomly incorporated in the crystal lattice, probably in the octahedral sites. The composition of 5 at. % Gd-doped magnetite was Fe_(3-x)Gd_xO₄ (x= 0.085 ± 0.002) determined by inductively coupled plasma-mass spectrometry (ICP-MS). Gd-doped nanoparticles exhibited ferrimagnetic properties with small coercivity and slightly decreased magnetization at 260 K in contrast to the undoped, superparamagnetic magnetite nanoparticles.

Vesicles have the potential to be utilised in many medical applications. Vesicles can be used to encapsulate drugs, for release at specific locations, meaning lower doses and improving treatment efficiency whilst reducing consequental side effects. Medical researchers are developing therapies which can simultaneously diagnose and treat a wide range of diseases, termed theranostic agents. Our research, is focussed on the development of magnetic vesicles for use as theranostic agents. We are combining the diagnostic capability of magnetic nanoparticles (MNPs), currently used in MRI scanning with their theraputic capability of magnetic hyperthermia to treat tumours. Magnetotactic bacteria synthesise magnetosomes, which are internally formed vesicles containing a biomineralised magnetite MNP. To be suitable for medical use, both vesicles and MNPs must be of a consistent size and shape, to ensure predictable behaviour. We takes inspiration from magnetic bacteria to create artifical magnetosome-like theranostic magnetic nanovesicles in situ under mild reaction conditions, which has been sucessfully achieved. MNPs in our system are precipitated within the vesicle membrane, and appear responsive in intial MRI and hyperthermia testing. The benefit of MNP precipitation within the vesicle membrane is that the core is free for encapsulation of hyrdrophillic drugs for delivery controlled by application of a magnetic field. Work is now focussed on the incorporation of biomineralisation and membrane iron-transport proteins from the magnetic bacteria into our vesicles to further control the MNPs size and shapes within the nanovesicles and thus tune the magnetic properties.

Magnetic nanoparticles dissipate heat in the presence of an alternating magnetic field. The wireless generation of a magnetothermal dosage can be used for a variety of biomedical applications, including cancer hyperthermia and deep brain stimulation. Ferrite nanoparticles synthesized by thermal decomposition of organometallic precursors are particularly suitable for these applications, yet variability in magnetic properties is reported even when the syntheses are based on the same reactive components. We find that redox-active solvents enables the synthesis of nearly defect-free ferrite nanoparticles with some of the highest heating efficiencies, or specific loss powers, reported to date at the lowest magnetic field frequency and amplitude product relevant for clinical applications. We demonstrate that these optimized nanoparticles enable rapid modulation of membrane voltage for wireless cellular control as well as enhancement of r2 relaxivity for use as potent T2 magnetic resonance imaging contrast agents.

Magnetic tunnel junctions (MTJs) with thin CoFeB layers and perpendicular anisotropy can be switched at much lower current densities (~10² A/cm²) than those with thicker layers, in-plane anisotropy, and spin transfer torque reversal (~10⁶ A/cm²) [1]. The perpendicular anisotropy arises from the CoFeB/MgO interface and its magnitude depends on the applied voltage [2]. Low power MTJs would be more compatible with existing CMOS transistors, provided the magnetic devices can be scaled to small sizes. Here we describe the fabrication of MTJs ranging from 20 to 500 nm and characterization of their switching as a function of magnetic field and voltage bias. Conductive atomic force microscopy (C-AFM) enables scanning magnetoresistance measurements of individual CoFeB/MgO/CoFeB MTJs. The CoFeB films were le; 1.6 nm and exhibited perpendicular anisotropy. Electron beam lithography and nanoparticle masking were used with reactive ion etching to pattern CoFeB/MgO/CoFeB tunnel junctions with diameters down to 20 nm. After scanning electron microscopy was used to determine the nanopillar diameters, the samples were imaged with the C-AFM. Topography and conductivity maps of the nanopillar patterns were collected simultaneously. Measurements of resistance as a function of magnetic field and voltage bias were made with the Pt-coated probe tip in stable contact with individual nanopillars. When resistance-area product was unchanged by the patterning process, field-dependent switching was reliably observed. Major and minor hysteresis loops were collected as a function of the applied magnetic field to determine the effective anisotropy of the free layer. At fields close to the coercivity the tunnel current showed random telegraph noise, and the effective anisotropy was also calculated from the switching statistics and comparison with Landau-Lifshitz-Gilbert modeling of the magnetization dynamics. Voltage induced switching of the free layer was observed in devices larger than 80 nm. The regimes of magnetization reversal by coherent rotation and domain wall nucleation are discussed, along with the prospects of extending the range to smaller low power devices.
1. W. Wang, M. Li, S. Hageman, and C. Chien, Nature Mater.,11, 64 (2012).
2. S. Ikeda, K. Miura, H. Yamamoto, K. Mizunuma, H. D. Gan, M. Endo, S. Kanai, J. Hayakawa, F. Matsukura, and H. Ohno,Nature Mater. 9, 721 (2010).

Magnetic sensors and low energy magnetic devices such as spin-transfer torque magnetic random access memories rely on the function of magnetic tunnel junctions (MTJs). As devices scale to smaller dimensions, it is essential to develop patterning processes to produce sub-100 nm MTJs and to understand the factors that control their switching field, tunneling magnetoresistance (TMR), and thermal stability. The variation in anisotropy between MTJ pillars affects both the reversal #64257;eld and thermal stability, and the TMR is sensitive both to the patterning process and the measurement voltage.
We present here a study of the resistance distributions, the TMR, and the switching #64257;eld in arrays of perpendicular magnetic tunnel junctions of 40 nm up to 2 µm in diameter using atomic force microscopy (AFM) and magnetometry. The nano-patterned MTJs were fabricated from films with a Mo underlayer, and the following composition Mo/CoFeB/MgO/CoFeB/Mo, using ion beam etching with a mask made from hydrogen silsesquioxane electron-beam resist. Highly localized electrical and magnetic property measurements were performed using nanoscale conductive AFM and magnetic force microscopy (MFM) on the nano-patterned MTJs in the remanence state following saturation and after ac demagnetization. Despite the thin layers (0.8 - 1.6 nm CoFeB), the up or down magnetic state of individual pillars was clearly distinguished by MFM, and the resistance distribution was measured from the current (nA to µA) with a bias voltage of 100 to 500 mV applied. The resistance of the pillars had a broad distribution reflecting differences in pillar area, edge condition, and local variations in the MgO layer. The application of relatively large bias voltages (1 to 4 V) to individual MTJ pillars or arrays induced significant changes in the resistance state. In this manner, the AFM can be used to “write” high and low resistance states with unique patterns and shapes on the nanoscale. This process could be used to further understanding the thermal stability and switching behaviour of nano-scale MTJs. The impact of the intrinsic anisotropy distribution in the MTJ pillars on the switching field will be discussed and mechanisms for localized current or voltage induced switching will be proposed.

Flexible electronics has emerged as a standalone field and matured over past decades offering the unique possibility to adjust the shape of devices at will after their fabrication. Flexible devices strongly benefited from the recent developments of organic as well as inorganic electronics, which are prepared using printing and/or thin film technologies.
To complete the family (transistors, displays, sensors, RFID tags, organic solar cells etc.), there are strong activities towards the fabrication of flexible magnetic field sensorics.^1-3 By now, high performance magnetic sensorics relying on the giant magnetoresistive (GMR) effect are prepared exclusively using cost intensive and complex thin film fabrication technologies,³ while the most straightforward solution would be to print magnetic sensing elements at pre-defined locations on flexible circuitry.
To assure applicability of the printed GMR sensors, they should provide stable response in the consumer temperature range from 0°C up to +85°C, which require careful optimization of the polymeric binder solution with respect to the thermal expansion coefficient. Furthermore, accounting for the relatively small amplification coefficient of available printable and flexible transistors, the GMR in the range of several tens of percent under moderate magnetic fields of about 0.5 T, provided by flexible rubber based NdFeB permanent magnets, needs to be demonstrated. Indeed, printable and flexible amplifiers exhibit a DC gain as high as 50 dB and could be coupled with printable magnetoelectronics possessing MR ratios of at least 30%.
Here, we demonstrate the very first high performance printable magnetic field sensorics applicable for flexible electronics. Remarkably, after printing, the GMR sensor elements reveal up to 37% change of the electrical resistance in the magnetic field with a maximal sensitivity of 0.93 T-1 in a field of 130 mT. Furthermore, the developed magneto-sensors are fully operational in the temperature range from -10°C up to +95°C, which fulfills the stringent thermal stability requirements of consumer electronics.⁴
With this performance, printed magnetoelectronic devices could be applied as passive components responding to a magnetic field for flexible electronics. Indeed, the output signal of the sensors can be conditioned using available printed and flexible active electronics. In combination with flexible and printable active electronics as well as wireless communication modules, the high performance magnetic field sensorics enables realization of complex platforms capable of detecting and responding to an external magnetic field. This feature is of great interest to realize smart packaging and energy efficient magnetic field driven switches.
References:
1. Makarov, D. et al.ChemPhysChem14, (2013).
2. Karnaushenko, D. et al.Adv. Mater.24, (2012).
3. Melzer, M. et al.RSC Adv.2, (2012).
4. Karnaushenko, D. et al.Adv. Mater.27, (2015).

Magnetic materials with large spin polarization at room temperature have been actively pursued in recent years for the development of next-generation spintronic devices. Thus far only a few materials have been found to exhibit complete spin polarization, referred to as half-metals. Chromium-based chalcospinels are the only chalcogenide containing materials with Curie temperature above room temperature. However, the magnetic and electronic properties of chromium-based chalcospinels at nanoscale level are not well understood. The exceptional spin polarization characteristics predicted for some of the chalcospinels motivated us to synthesize them as nanodimensional crystals and study their magnetic properties. We have developed a facile colloidal method for the synthesis of CuCr₂S_xSe_4-x nanocrystals over the entire composition range involving hot injection of a mixture of 1-dodecanethiol and diphenyldiselenide into a hot capping ligand containing CuCl₂ and CrCl₃.6H₂O. Systematic changes in the lattice parameter and EDX elemental composition determination confirm formation of CuCr₂S_xSe_4-x alloy nanocrystals. The dimensions of the nanocrystals, as determined from TEM images, vary from 12 ± 1.4 nm to 21 ± 1.4 nm. The Curie temperature (T_C), estimated from magnetization (M) as a function of temperature (T), shows a systematic increase with increasing selenium content. Saturation magnetization and coercivity values of CuCr₂Se_xS_4-x nanocrystals at 5 K are found to steadily increase up to x = 3. Electronic structure calculations using density functional theory as a function of composition and size suggest ferromagnetic ordering over the entire composition range with nearly half-metallic characteristics for the bulk. Moreover, the calculations predict full opening-up of a gap at the Fermi level in the minority spin channel at reduced dimensions to make them a “complete” half-metallic system

Most Spintronic applications for energy-saving electronics and data storage require the use of the chosen functional material in the form of thin film, so the possible changes of properties inherent to the scale reduction or the presence of a substrate needs to be taken into account and tackled to guarantee that thin film specimens present the same or even optimized functional properties with respect to their bulk counterparts. An ideal benchmark to study these effects is single crystalline La_2/3Ca_1/3MnO₃ (LCMO), a colossal magnetoresistive spin-polarized ferromagnet (FM) which often presents a dramatic reduction or weakening of their magnetic and transport properties in thin film. Saturation magnetization, Curie temperature, and conductivity can be dramatically reduced by the epitaxial strain induced in their crystal structure by the substrate, which in many cases have been associated to the formation of a magnetically dead layer at the interface with the substrate [1].
In this work we have investigated the alteration of the magnetic properties of epitaxially LCMO thin films by locally imaging the remanent magnetization distribution through Electron Holography (EH) experiments at 100 K. For this study, we have altered the degree and sign of epitaxial strain induced by the substrate by growing it on different (001)-oriented substrates: (LaAlO₃)_0.29-(Sr_0.5Al_0.5TaO₃)_0.71 (LSAT) [unstrained films], SrTiO₃ (STO) [films with tensile strain], and LaAlO₃ (LAO) [films with compressive strain]. In correlation with macroscopic magnetization measurements. EH experiments have revealed the formation of a magnetically phase-segregated LCMO films upon tensile-induced strain, where an antiferromagnetic (AFM) layer is formed in the free surface of the manganite on top of the FM layer, which might be the first direct observation of the formation of a magnetic dead layer [2]. This strain-induced single-phase FM/AFM bilayer can be exchanged coupled, suggesting a new route for the design of pinning layers in spin valve architectures using a single material. In the case of compressively strained LCMO, a complex change of the magnetic anisotropy in LCMO films has been observed, with an out-of-plane magnetization easy axis. These results provide the key ingredients to understand the importance of epitaxial strain in the magnetic behavior of single crystal LCMO films.
References
[1] Y. Lu et. al., Phys.Rev.B73 (2006) 184406.
[2] L. Marín, L. A. Rodríguez, et. al., Nano Lett. 15 (2015) 492.

Strain annealed magnetic nanocomposites have recently been investigated for inductors, transformers, sensors, motors, and other magnetic applications. We have previously demonstrated induced magnetic anisotropies, K_u&’s, in strain annealed Co-based metal/amorphous nanocomposites (MANCs) with a response to applied stress twice that of Fe-based MANCs [1] and an order of magnitude larger than field annealed Co-based MANCs [2-3]. Transverse magnetic anisotropies and switching by rotational processes impact anomalous eddy current losses at high frequencies [4]. A phenomenological model for multi-phase resistivity in MANCs identifies implications for classical eddy current losses [5,6]. Here we report on Co-based MANCs having 4-5 times the response to strain annealing as compared to Fe-based MANC systems. This response is correlated with the concentrations of early transition metal (TE) growth inhibitors that systematically increase both induced anisotropies and resistivities in new alloys. These alloys exhibit nearly perfectly linear B-H loop, with low tunable permeabilities. Induced anisotropy values for these systems do not depend on the alloy magnetostriction but correlate strongly with virtual bound states (VBS). The electrical resistivity is not a function of stress but trends in electrical resistivity and induced anisotropy with the choice and concentration of early transition metal growth inhibitors (which contribute VBSs) are made. Previously reported induced anisotropies, K_u, ~2 x 10⁵ erg/cc (anisotropy fields, H_K > 200 Oe), in strain annealed Co-rich NCs have been increased to K_u, ~5 x 10⁵ erg/cc (H_K > 500 Oe) in new systems.

Cobalt based metallic glasses have attracted lot of interest due to their remarkable soft magnetic properties, ultra-low coercivity (~ 1 A/m), low remnant magnetization (M_r), and very low saturation magnetostriction (l_s =10^-7 ppm). Lack of grain boundaries in metallic glasses with homogeneous isotropic structure promote high saturation magnetization and low hysteresis losses making them attractive for a number of soft magnetic applications including electric transformers, motors, electro-magnetic shielding and fluxgate sensors. Here, we report the effect of nanocrystallization on the transformation of soft-magnetic properties of a Co-based metallic glass as shown in Figure 1. A drastic change in magnetic properties was found in going from fully amorphous state to a mixture of nano-crystalline and amorphous to fully devitrified form. The coercivity (H_c) changes from amorphous soft magnetic state (H_c~ 0.12 Oe) to nanocrystalline dispersed hard magnetic state H_c~ 187 Oe (15,000 A/m), along with a significant change in remnant magnetization (M_r).

Upon the increasing demand for the miniaturization of electromagnetic devices, it is inevitable to reduce the volume/size of magnetic components such as inductors and transformers. To minimize the size of inductors, high operating frequencies and exploitng soft magnetic core materials with low energy loss are required to increase the power density of the system. In this aspect, magnetic nanocrystals are intriguing materials due to their superparamagnetic behavior. Soft magnetic nanocrystals exhibit rapid spin relaxation due to thermally induced magnetic reorientation at above their blocking temperature. Because of the fast spin relaxation, magnetic nanocrystals can operate at high AC magnetic frequencies. In addition, their tunable magnetic properties and the capability for solution based fabrication processes make nanocrystals more attractive to the magnetic cores of inductors. However, the size, shape, and composition dependent magnetic permeability of nanocrystals is rarely studied^1-3 and the lack of understanding in AC magnetic properties of nanocrystals limits the utilization of magnetic nanocrystals at radio frequencies. In our work, the DC and AC magnetic properties of nonstoichiometric zinc ferrite nanocrystals are investigated. Nearly monodisperse Zn_xFe_3-xO₄ nanocrystals with controlled size (7.4 nm to 13.8 nm) and composition (x=0 to 0.25) are synthesized through high temperature thermal decomposition process. DC magnetic characterization with SQUID magnetometry reveals that the saturation magnetization of the nanocrystals rises as the size and the amount of Zn in the nanocrystals increase. Due to increased saturation magnetization, the real part of magnetic permeability of 12.3 nm Zn_0.25Fe_2.75O₄ nanocrystals show almost two times higher value in the frequency range from 1 MHz to 500 MHz than that of iron oxide nanocrystals with similar size. Finally, the inductance, resistance, and quality factor of a microfabricated inductor with 12.3 nm Zn_0.25Fe_2.75O₄ nanocrystal core are measured and indicate that zinc ferrite nanocrystals can be a promising candidate for magnetic core materials operating in radio frequencies.
This work was supported primarily by the Department of Energy&’s Advanced Research Projects Agency-Energy (ARPA-E) DE-AR0000123. J.M.K. acknowledges the MRSEC program of the National Science Foundation for support under Award No. DMR-11-20901.
References
[1] H. Yun, X. Liu, T. Paik, D. Palanisamy, J. Kim, W. D. Vogel, A. J. Viescas, J. Chen, G. C. Papaefthymiou, J. M. Kikkawa, M. G. Allen, and C. B. Murray, ACS Nano, 2014, 8, 12323
[2] N.-N. Song, H.-T. Yang, H.-L. Liu, X. Ren, H.-F. Ding, X.-Q. Zhang, and Z.-H. Cheng, Scientific Reports, 2013, 3, 3161
[3] H. Kura, T. Ogawa, R. Tate, K. Hata, M. Takahashi, J. Appl. Phys., 2012, 111, 07B517

Magnetic nanoparticles (NPs) such as SuperParamagnetic Iron Oxide Nanoparticles (SPIONs) are widely used in various biomedical applications (hyperthermia, drug delivery and T2 contrast agents for Magnetic Resonance Imaging (MRI)) thanks to their chemical and biological properties [1,2]. This multimodal probe is a great tool for theranostic which combines diagnosis and therapy.
In this work, a multimodal imaging magnetite (Fe3O4) nanoparticle used as contrast agent for MRI/PET (Positron Emission Tomography) double imaging has been developed. In a first step and by means of a continuous hydrothermal process, surface-modified NPs are prepared with a very narrow size distribution [3]. Hydrophilic organic molecules namely citric acid (CA), 3,4-dihydroxy-L-phenylalanine (L-DOPA) and 3,4-dihydroxyhydrocinnamic acid (DHCA) have been grafted onto the surface of NPs during the synthesis process [4]. A crystallite size change of the modified magnetite NPs and an anti-oxidizing effect are proved by both TEM and X Ray Diffraction (XRD) analyses [3,4]. The stability of the surface-modified NPs suspensions in water has been improved at physiological pH. Raman, Infra-Red and X Ray Photoelectron (XPS) spectroscopies, combined with zetametry measurements highlight the grafting of organic molecules [4].
The second step consists in developing stable complexes with radionuclides on the surface-modified NPs with a chelating agent. 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) or 2,2'-(7-(1-carboxy-4-((2,5-dioxopyrrolidin-1-yl)oxy)-4-oxobutyl)-1,4,7-triazonane-1,4-diyl) diacetic acid (NODAGA) derivatives have been used in order to ensure the chelation of copper (64Cu) for PET imaging. Polyethylene glycol (PEG) has also been grafted onto NPs surface in order to improve their stealth. To confirm and quantify the grafting of macrocycles and PEG chains on modified NPs, specific surface area measurements, IR, XPS, TGA, zeta-potential, DLS and elemental analysis measurements have been realized.
In vitro and in vivo results will be presented. Yields of radiolabeling are good and show that the radioactive tracer is chelated by the macrocycles on the NPs surface. Biodistribution of NPs will be presented. It will be shown that the results depend mainly of the NPs surface charge [5].
These nanohybrids appear as promising contrast agents for MRI/PET double imaging in view of cardiovascular diseases imaging.
[1] J. Boudon, J. Paris, Y. Bernhard, E. Popova, R.A. Decréau, N. Millot, Chem. Commun, 2013, 49, 7394-7396.
[2] L. Maurizi, H. Bisht, F.Bouyer, N.Millot, Langmuir 2009, 25, 8857-8859.
[3] L. Maurizi, F. Bouyer, J. Paris, F. Demoisson, L. Saviot, N. Millot, Chem. Commun., 2011, 47, 11706-11708.
[4] G. Thomas, F. Demoisson, R. Chassagnon, E. Popova, N. Millot, submitted to Dalton Trans.
[5] L. Maurizi, A.L. Papa, L. Dumont, F. Bouyer, D. Vandroux, P. Walker, N. Millot, J. Biomed. Nanotechnol. 2015, 11, 126-136

The understanding of the molecular mechanism of disease progression in atherosclerosis has resulted in a shift towards visualizing plaque morphology through several imaging modalities for both diagnostic and prognostic means. Imaging technology for detecting vulnerable plaques include intravascular ultrasound (IVUS), computed tomography (CT), positron emission tomography (PET), angioscopy, and magnetic resonance imaging (MRI); these imaging techniques have made great strides to assess the vulnerability of atherosclerotic plaques through morphological attributes in the last two decades, but poor sensitivity, limited accuracy, or concerns regarding safety and cost efficiency inhibit their use for clinical or practical application for preventive measures.
Out of the existing technologies, MRI is a promising tool to characterize plaque morphology due to its superior capability of determining plaque size and composition with reasonable accuracy and reproducibility. Nonetheless, MRI is limited and similar to other technologies in that it aims to assign physical traits to assess the molecular state of a plaque. The next challenge is to image and quantify molecular markers in vivo to accurately determine plaque progression.
To that end, we report on gadolinium incorporated, fibrin-targeting, spherical peptide amphiphile micelles (PAMs) for detecting late-stage plaques. Micelles consisted of DSPE-PEG2000-CREKA, DSPE-PEG2000-Cy7, and DSPE-DTPA(gadolinium) and were determined to be approximately 20 nm in diameter via dynamic light scattering and transmission electron microscopy. T1 and T2 relaxivities of micelles altered in a gadolinium-dependent manner, and were in range of contrast agents used clinically. Moreover, micelles were found to be biocompatible in vitro and displayed specific binding to clots. Due to the modularity of PAMs and their ability to incorporate multiple components, our investigations will lay the ground work for PAM-mediated theranostic applications to provide a molecular imaging tool that can bind to specific markers of interest, deliver a therapeutic, and monitor the progression and regression of the disease in real-time.

Medical imaging is widely used in the staging and diagnosis of various medical conditions.¹ In particular, magnetic resonance imaging (MRI) is vital for visualizing organs and soft tissue. Globally, ~60 million MRI procedures are performed each year, and ~20 million of them use Gadolinium-based contrast agents (GBCAs).^2-4 Although GBCAs are cleared within 24 hours in patients with normal renal function, impaired renal function can significantly increase this clearance time, potentially leading to severe adverse effects such as the untreatable nephrogenic systemic fibrosis.⁵ This has triggered a U. S. Food and Drug Administration (FDA) black box warning and a contraindication of GBCA for patients with impaired kidney function. The number of patients potentially affected (stage 3+ Chronic Kidney Disease) is increasing and presently consists of more than 26% of the population with age 60+.⁶ In order to provide a gadolinium-free contrast agent with pharmacokinetic properties comparable to GBCAs, we have designed and developed a new class of superparamagnetic iron oxide nanoparticles (SPIONs), consisting of ultra-small inorganic cores and ultra-thin hydrophilic shells. These SPIONs are qualitatively different from previously described SPIONs⁷ in that they show both renal clearance, and a high T₁ contrast power.
References:
1. Harisinghani, M. G., Barentsz, J., Hahn, P. F., Deserno, W. M., Tabatabaei, S., van de Kaa, C. H., de la Rosette, J. & Weissleder, R. New England Journal of Medicine 348, 2491-U2495, (2003).
2. McDonald, M. A. & Watkin, K. L. Academic Radiology 13, 421-427, (2006).
3. Na, H. B., Lee, J. H., An, K. J., et al. Angewandte Chemie-International Edition 46, 5397-5401, (2007).
4. Centers for Medicare & Medicaid Services, 2014 ASP Drug Pricing Files
5. Perez-Rodriguez, J., Lai, S., Ehst, B. D., Fine, D. M. & Bluemke, D. A. Radiology 250, 371-377, (2009).
6. Kidney Disease Statistics for the United States. National Kidney and Urologic Diseases Information Clearinghouse, (2012).
7. Ittrich H, Peldschus K, Raabe N, Kaul M & G., A. Fortschr Röntgenstr 185, 1149-1166, (2013).
Our related publications:
1. Wei H, Bruns OT, Kaul MG, et al. “Exceedingly-Small Iron Oxide Nanoparticles as Positive MRI Contrast Agents” submitted
2. Chen O, Riedemann L, Etoc F, Herrmann H, Coppey M, Barch M, Farrar CT, Zhao J, Bruns OT, Wei H, et al.Nature Communications. 2014, 5, #5093
3. Chen O, Wei H, Maurice A, Bawendi MG, Reiss P. MRS Bulletin. 2013, 38, 696-702.
4. Wei H, Bruns OT, Chen O, Bawendi MG. Integrative Biology. 2013, 5, 108-114.
5. Wei H, Insin N, Lee J, Han HS, Cordero JM, Liu W, Bawendi MG. Nano Letters. 2012, 12, 22-25.

Superparamagnetic iron oxides (SPIOs) are one of the extensively used magnetic resonance imaging (MRI) contrast agents (CAs) for medical diagnosis and therapy. We herein report the fabrication of novel, potential platforms based on SPIO nanoribbons (SPIONRs) effectively integrated with chemically-reduced graphene oxide (rGO/SPIONRs), and test their efficacy as high-relaxivity MRI CAs through T2-weighted phantom imaging. High-quality SPIONRs were synthesized via a peptide-modified co-precipitation approach, whereas rGO was synthesized in situ via a facile hydrothermal route. X-ray diffraction, advanced spectroscopy, electron microscopy and magnetometry were applied to elucidate the formation, surface morphology, composition, superparamagnetic response, phase and functionalization of the hybrid material. Our findings indicate that the chemical surface of elongated nanoribbons exhibits superior magnetic dipole interaction (with relaxivity values of ~100 mM-1s-1 higher than those found in commercial formulations used in hospitals), which is apparently reflected upon the orientation of the magnetic moment that in turn induces a strong field gradient of local sites. The tolerance of SPIONRs in cancer cells in absence and presence of an external magnetic field at 1.41 T will be also presented.

P(DEGMA-co-OEGMA-b-[TMSPMA-co-VBA])@silica@magnetite polymer-nanoparticle composites have been developed as a platform for controllable drug release. The nanocomposite facilitates controllable release of therapeutic molecules through breakage of pH and heat labile Schiff base bonds that bind the molecules to the polymer. This enables dual-stimuli responsive drug release in response to the acidic microenvironment of cancerous cells and heat generated by the magnetite nanoparticles when subjected to an alternating magnetic field, thereby permitting spatial and temporal control over ‘burst&’ release of the drugs. The nanocomposite has also been shown to be effective at improving magnetic resonance imaging contrast through enhancement of spin-spin relaxivity.

Magnetism is tightly associated with magnetic element organization within a crystal structure. When the magnetic components are also catalytically active, catalytic properties of the elements can then be correlated not only with structure, but also with magnetism. The magnetism of a nanoparticle is known to be size, shape and composition dependent. By controlling synthetic parameters, nanoparticle magnetism can be controlled from superparamagnetic to ferromagnetic and accordingly catalytic properties can be tuned to optimization. Using metallic Co, ferrite and FePt as examples, I will demonstrate how to control nanoparticle structure, magnetism and catalysis for important energy conversion and biological detection.

Magnetic nanowires fabricated by electrodeposition have unique properties which make them advantageous for use in cell separation and magnetic resonance imaging (MRI). First, the nanowire&’s high aspect ratio gives it inherent magnetic anisotropy and a large surface area to volume ratio, which makes it ideal for magnetic, antibody-based cell separation. In this work, multilayer Au-Ni-Au, Au-Fe-Au, and Ni-Fe-Ni nanowires were compared for use in magnetic cell separation of T cells, from a single cell suspension harvested from C57BL/6 mice, using an MHC class II monomer which has a histidine and biotin group. The dual functionality of the monomer means it may be directly attached to Ni nanowires via histidine or NH₂-PEG-COOH-streptavidin-biotin or to Fe NWs via SH-undecanoic acid-streptavidin-biotin linkage. The nanowire-monomer conjugates were tagged with fluorescent streptavidin and cell separation efficiency was measured using fluorescence-activated cell sorting (FACS). The separation efficiency was compared for various length nanowires. The Au-Fe-Au nanowires appear to be more effective than the Au-Ni-Au nanowires for cell separation. The Ni and Fe nanowire dose dependence was measured, as well as the optimal layering. In addition to cell separation, the T1 and T2 relaxation properties of multilayer Au-Fe-Au magnetic nanowires were measured using a relaxometer to compare the relaxation properties of Fe segments with various aspect ratios and different nanowire surface coatings. Ni and Fe nanowires were then imaged using gradient echo recall (GRE) and Sweep Imaging with Fourier Transformation (SWIFT). The Ni nanowires showed T2 shortening while the Fe nanowires showed T1 and T2 shortening effects.

Superparamagnetic iron oxide nanoparticles (SPIONs) are an exciting class of materials with regard to biomedical applications owing their exceptional magnetic properties, high biocompatibility and chemical stability. These favorable characteristics have continuously increased their demand as unique contrast agents for magnetic resonance imaging (MRI) in clinical diagnostics. Therefore, enormous research has been performed during the last years to develop novel straightforward and safe synthetic routes for iron oxide based MRI contrast agents which also includes a scaling-up potential.
Herein we report a green and facile one-pot synthesis for the preparation and in situ functionalization of water-soluble and biocompatible iron oxide nanoparticles. Therefore, we used two classes of naturally available nutrients namely ascorbic acid (vitamine C) and green tea catechins. In the first approach, easily water-dispersible crystalline SPION_S were produced in a hydrothermal synthesis using ascorbic (vitamin C) as reducing agent whereby the oxidation product instantly formed a protecting and stabilizing layer around the particles. Besides their high biocompatibility, which was confirmed by in vitro assays, the resulting particles showed enhanced r₂/r₁ ratios compared to the clinically approved contrast agent Sinerem.
In this context we further developed the synthesis of iron oxide nanoparticles using green tea catechins. Green tea is a promising material which additionally exhibits beneficial antioxidative, anticancer and anti-inflammatory effects. Obtained green tea functionalized SPIONs were long-term stable in water dispersions, biocompatible and efficiently taken up by human macrophages and colon cancer cells. Furthermore, in vivo studies revealed high accumulations in tumor tissues similar to clinically approved contrast agents. High relaxivity values were obtained resulting in strong contrast enhancements which further support their employment as novel MRI contrast agents in clinics.

Due to iron toxicicity, magnetic iron oxide nanoparticles (NPs) need to be coated with biomacromolecules (e.g., Dextran) for biomedical applications. Here we use an inorganic, highly biocompatible calcium phosphate (CaP) layer to encapsulate magnetic iron oxide. The formed magnetic calcium phosphate (MCaP) nanoparticles are highly biocompatible, strongly paramagnetic, and easy for chemical functionalization. To demonstrate the suitability of MCaP nanoparticles for viarous biomedical applications, we tested in two different research projects. In one project, MCaP NPs were mixed with monomer of bone cement and reduced amount of free-radical initiator. Under an alternating magnetic field, MCaP NPs were able to generate heat and induced the polymerization of bone cement. Moreover, the magnetic bone cement has slightly improved mechanical properties, radio opacity, and biocompatiblity compared to regular bone cement without X-ray contrast agent. In another project, MCaP NPs were loaded wtih a chemo drug and Near-infrared imaging agent and injected into a subcutaneous prostate tumor in mice. It was demonstrated that tumor growth was significantly inhibited due to the drug released and heat generated from MCaP NPs, Moreover, tumor-bearing mice treated with drug-loaded MCaP NPs also resulted in signifcant reduction in lung cancer metastasis. Both projects demonstrated that novel MCaP NPs are promising for various biomedical applications (imaging, drug delivery, hyperthermia, etc).

Nanoscale or microscale magnetic particles have been exploited for enabling the ability of magnetic manipulation and the ability of signal amplification. This type of manipulation is very important for biomolecular detection. One area of increasing interests is the development of these abilities for cancer detection. A key strategy is the exploration of the multi-functionality of the magnetic nanoprobes for specific targeting of biomarkers which is a coherent indicator for the stage of cancer or other diseases. This report describes new findings of our recent investigations of functional NiFe magnetic nanoprobes by coating NiFe core with Au shell for ultrasensititve detection of cancer biomarkers. One example involves the detection of carcinoembryonic antigen (CEA) using nanoparticle-enhanced SERS technique. The magnetic core-Au shell nanoparticles synthesized by wet chemical methods, are in the formation of sandwich structure complex with the specific antibody. The targeted CEA are detected after separation by applying a magnetic field. The results demonstrated a low detection limit, showing a great promise of utilization of functional magnetic nanoprobes in cancer biomarker detection.