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.
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