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 conte