Symposium FF
Magnetic Materials for Energy

Session FF-1 - Hard Magnetic Materials

FF-1:IL01  Material Criticalities in Magnetism
O. GUTFLEISCH, TU Darmstadt, Material Science, Germany; Fraunhofer Project Group Materials Recycling and Resource Strategy IWKS, Hanau, Germany

Due to their ubiquity, magnetic materials play an important role in improving the efficiency and performance of devices in electric power generation, conversion and transportation 1. Permanent magnets are essential components in motors and generators of hybrid and electric cars, wind turbines, etc. Magnetocaloric materials could be the basis for a solid state energy efficient cooling technique alternative to compressor based refrigeration. Any improvements in magnetic materials will have a significant impact in these areas, on par with many “hot” energy materials efforts (e.g. hydrogen storage, batteries, thermoelectrics, etc.).
The talk focuses on rare earth and rare earth free permanent magnet and magnetocaloric materials with an emphasis on their optimization for energy and resource efficiency in terms of the usage of critical elements. The synthesis, characterization, and property evaluation of the materials will be examined briefly having in mind their critical micromagnetic length scales and phase transition characteristics.
1. O. Gutfleisch, J.P. Liu, M. Willard, E. Brück, C. Chen, S.G. Shankar, Magnetic Materials and Devices for the 21st Century: Stronger, Lighter, and More Energy Efficient (review), Adv. Mat. 23 (2011) 821-842.
2. J. Liu, T. Gottschall, K.P. Skokov, J.D. Moore, O. Gutfleisch, Giant magnetocaloric effect driven by structural transition, Nature Mat. 11 (2012) 620-626+suppl.


FF-1:IL02  A Multi-scale Approach to Develop High Coercivity Dy-free Permanent Magnets
H. SEPEHRI-AMIN, J. LIU, T. AKIYA, T. OHKUBO, K. HONO, Elements Strategy Initiative Center for Magnetic Materials, National Institute for Materials Science, Tsukuba, Japan; K. HIOKI, A. HATTORI, Daido Corporate Research & Development Center, Daido Steel Co. Ltd., Nagoya, Japan

Anisotropic Nd-Fe-B sintered magnets are currently known as the highest performance permanent magnets. However, low coercivity is the main drawback for high temperature applications such as traction motors of hybrid cars. One approach to enhance the coercivity is the reduction of grain size. Hot-deformed anisotropic Nd-Fe-B magnets, which comprise of ultra-fine platelet-shaped Nd2Fe14B grains, have the potential to attain a much higher coercivity than that of Nd-Fe-B sintered magnets. However, the highest coercivity reported so far was only 1.8 T without Dy [1].We have performed thorough microstructure characterization of the hot-deformed magnets processed with various conditions using SEM, STEM and 3DAP and correlated the grain size and the chemical composition of the intergranular phase with coercivities. In pararell, we have performed finite element micromangnetic simulations to deduce the ideal platelet grained microstructure to attain the highest coercivity. Based on these resutls, we employed low temperauture grain boundary diffusion process using Nd-Cu based eutectic alloys, thereby ehnacing the coercivities of bulk hot-deformed magnets substantially with minimum loss of remanence.
[1] J. Liu et al. Acta Mater. 61 (2013) 5387.


FF-1:IL03  Approaches for the Discovery and Design of New Permanent Magnets
M.J. KRAMER, R.T. OTT, D.D. JOHNSON, Ames Laboratory, Iowa State University, Ames, IA, USA

Concern for supply restrictions of rare-earth metals has spurred intense interest in the discovery of new compounds that do not contain critical elements yet still exhibit high saturation magnetization and intrinsic coercively. There have also been efforts in optimizing magnetic properties in older alloys. Both are daunting tasks given the high energy product of existing rare-earth based alloys. Criticality of Dy, in particular, is driving the need to developing new alloys for the higher operating temperature regime of traction motors and some generators. Discovery of new compounds, however, requires a more sophisticated approach than simple "trial and error". Ames Laboratory, in collaboration with a number of universities and laboratories have been embarking on a comprehensive research program to combine a series of integrated computational and experimental efforts to both discover and design new compounds with promising magnetic properties. Experimental materials discovery will include both bulk and thin film combinatorial synthesis. Additionally, we are developing high throughput thermal analysis and in situ XRD capabilities to characterize the phase space of these multi-elemental libraries as a function of temperature. The computational efforts of this research include both density functional theory and adaptive genetic algorithms to identify new compounds.  Specific examples of materials discovery and new insights into improvements of existing alloys will be presented.


FF-1:IL04  Permanent Magnetic Materials for Energy Conversion and Power Generation: New Materials, New Designs
L.H. LEWIS, Northeastern University, Boston, MA, USA

Permanent magnet development has historically been driven by the need to supply larger magnetic energy in ever-smaller volumes for incorporation in an enormous variety of applications, including clean energy technologies. While the so-called rare-earth "supermagnets", comprised of iron, cobalt and rare-earth elements such as Nd, Pr and Sm, remain the choice magnetic material for advanced applications, new materials are under investigation in light of current market and supply pressures on constituent rare earth elements. In this presentation, prospects and candidates for replacing rare-earth-based magnetic alloys with materials comprised of more abundant and less strategically-important elements are discussed. Magnetic materials design principles are examined from micro-, nano- and Angstrom-scales perspectives, and new results concerning rare-earth-free magnetic materials will be presented. Particular attention will be devoted to highlighting underdeveloped routes for realizing strong magnetic anisotropy.
Research supported by the U.S. Office of Naval Research, the National Science Foundation and ARPA-E (Advanced Research Projects Agency-Energy).


FF-1:L05  Modelling of Anisotropy and Coercivity in Novel Hard Magnets
J. FIDLER, A. ASALI, P. TOSON, W. WALLISCH, Vienna University of Technology, Institute of Solid State Physics, Vienna, Austria

The search for candidates of suitable magnetic materials, structures and their expected behavior as reduction of the dysprosium content or the replacement for rare earth containing permanent magnets is of great economical and scientific interest. We have performed first principle calculations based on the density functional theory (DFT) to determine the magnetocrystalline anisotropy of the rare earth (RE) intermetallic compounds RECo5 and RE2Fe14B. The aim is to obtain K1 values in dependence on the crystal lattice distortion and the substitution of rare earth atoms within the unit cell in order to understand the effect of the variation of crystal anisotropy near grain boundaries in sintered rare earth permanent magnets. Finite element micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation for magnetization reversal have been carried out in order to study the influence of the microstructure on the hysteresis properties. On the basis of DFT calculations and numerical micromagnetics we have analysed the limits of crystal anisotropy and shape anisotropy on the optimization of magnetization reversal processes in order to improve the coercive field of advanced hard magnetic materials.
The support from the EC projects ROMEO and REFREEPERMAG is acknowledged.


FF-1:IL06  MnBi Hard Magnets
G.C. HADJIPANAYIS, N.V. RAMA RAO, University of Delaware, Newark, DE, USA

The recent rare earth crisis has led to intense worldwide efforts to develop rare earth-free permanent magnets as a viable alternative to the present rare earth permanent magnets. Among the current materials considered, MnBi is the most potential candidate due to the large magnetocrystalline anisotropy (K ≈ 107 erg/cc) of the low temperature MnBi phase (LTP). Furthermore, MnBi displays a large coercivity at high temperatures as compared to the Nd2Fe14B magnets and therefore, it is a good candidate for high temperature applications. However, the LTP forms through a peritectic reaction at relatively low temperatures, and hence it is difficult to synthesize a single phase MnBi magnet by conventional synthesis techniques such as arc-melting and powder sintering. Several approaches have been adopted to synthesize high purity MnBi with good magnetic properties, including high-temperature sintering followed by magnetic separation, melt-spinning and low energy ball milling techniques. In this presentation we will review our research efforts on MnBi for the past couple of years and discuss the challenge that need to be overcome in order to realize the full potential of MnBi magnet.
Work supported by Siemens and NSF G8.


FF-1:IL07  Effects of Hydrogen on the Magnetic Properties of Rare-earth Iron Intermetallics for Energy
O. ISNARD, Université Grenoble Alpes, Inst NEEL, Grenoble, France; CNRS, Institut NEEL, Grenoble, France

The effect of hydrogen insertion on the physical properties of intermetallic compounds containing iron and rare earth elements has attracted much interest during the last years. Indeed, these alloys exhibit interesting properties from both fundamental and applied point of view in particular in the context of energy. The magnetic properties of some iron rich compounds (like Nd-Fe-B) have been shown to be very sensitive to the hydrogen content and Hydrogen is also know to be useful for some processing of high performance magnets . More recently, the intensive research for efficient magnetocaloric materials has led to the discovery of so called giant magnetocaloric effect materials like La(Fe,Si)13, whose magnetic performance can be optimized by hydrogen insertion into the lattice. However the understanding of the effects of hydrogen on the magnetic properties of rare-earth transition metals intermetallics is not straightforward since this involved both magnetic sub lattices and their interactions. Using a few examples, we will review and discuss the main effects of hydrogen insertion on the structural and magnetic properties of iron containing intermetallics interesting for energy.


FF-1:IL08  High Performance Hard Magnetic Thick Films
N.M. DEMPSEY, D. LE ROY, N. GUNDUZ-AKDOGAN, O. AKDOGAN, D. GIVORD, Univ. Grenoble Alpes, Inst NEEL, Grenoble, France; CNRS, Inst NEEL, Grenoble, France

High performance hard magnetic materials are of growing importance for clean energy technologies (hybrid electric vehicles, gearless wind turbines.) and have great potential for use in energy related micro-systems. In this talk we will report on the preparation and study of hard magnetic materials in thick film form. On the one hand these films serve as model systems to study magnetization reversal, with the aim of guiding the development of heavy rare earth free bulk magnets. On the other, the micro-patterning of such films is being developed for their integration into micro-systems.


FF-1:L09  Development of L10 Tetragonal Phase in Continuous and Nanopatterned Fe-Pd Films by Post-deposition Annealing
P. TIBERTO¹, G. BARRERA¹, F. CELEGATO¹, M. COISSON¹, F. VINAI¹, P. RIZZI², ¹INRIM, Electromagnetism Division, Torino, Italy; ²Chemistry Dept, Università di Torino, Torino, Italy

Tetragonal intermetallic phases such as FePt, CoPt and FePd are currently intensively studied as active ferromagnetic materials for high-density data storage due to their high magnetocrystalline anisotropy. As an alternative, arrays of ordered nanostructures with high magnetic anisotropy have been produced by conventional and self-assembling nanolithographic techniques. Polystyrene nanosphere lithography has been recently exploited for magnetic thin films nanostructuring on large scale. Fe50Pd50 thin films having thickness t 35 nm have been deposited onto Si substrates by sputtering technique. As-deposited films consist of a Fe50Pd50 disordered solid solution, being deposited without heating the substrate. Patterned FePd films were obtained by assembling on the continuous thin films commercially available PNs into a monolayer (starting mean diameter in the interval 100 ÷ 800 nm). The order-disorder transformation towards the L10-ordered hard magnetic phase has been induced by post deposition annealing (600 °C for 1200 s). The effect of patterning (i.e. dot diameter and mutual distance) on the hard magnetic properties will be highlighted. The magnetic properties of annealed samples have been studied and correlated with film microstructure.


FF-1:IL10  Fabrication of Nanostructured Permanent Magnets - Approaches from the Bottom
J. PING LIU, Department of Physics, University of Texas at Arlington, TX, USA

Exchange-coupled nanocomposite magnets are regarded as the next generation of permanent magnetic materials, based on the theoretical predictions. However, many fundamental questions and technical challenges remain. To understand the inter-phase exchange interactions and to fabricate bulk nanocomposite magnets with enhanced energy products, we have worked decade long in both the fundamental research and the materials processing technologies. Particularly, we started the bottom-up approaches in fabricating bulk nanocomposite magnets. Novel methodology for nanoparticle synthesis including the salt-matrix annealing, surfactant-assisted ball milling and severe plastic deformation have been developed. Unconventional compaction techniques including warm compaction and dynamic compaction are adopted because they can be used to retain desired nanoscale morphology for effective exchange coupling in bulk nanocomposite magnets. A perspective on fabrication of anisotropic nanocomposite magnets will be also discussed.
Work supported by DoD/DARPA, MURI, ARO, DoE/ARPA-E and NSF.


FF-1:L11  Influence of Mechanical Milling on Properties of SrFe12O19 and SrFe12O19/Fe0.65Co0.35; SrFe12O19/FeCoSiB Hard/Soft Magnetic Nanocomposite
M.N. GUZIK, S. DELEDDA, B.C. HAUBACK, Institute for Energy Technology, Kjeller, Norway; A. BOLLERO, E. BERGANZA, IMDEA Nanociencia, Campus Universitario de Cantoblanco, Madrid, Spain; A. QUESADA, J.F. FERNÁNDEZ, Instituto de Cerámica y Vidrio, CSIC Kelsen, Madrid, Spain; A.M. ARAGÓN, P. MARIN, Instituto de Magnetismo Aplicado, Las Rozas, Madrid, Spain

Investigations on permanent magnets employ mechanical milling (MM) to synthesize and tailor microstructural as well as magnetic properties of many single phases. In addition, MM techniques are used for the synthesis of new nanocomposites based on magnetically soft/hard materials. High value of coercivity can be achieved in a hard magnetic phase with a grain size close to a single domain particles size. On the other hand, a hybrid material potentially used as an exchange spring magnet needs to contain a soft magnetic phase with a grain size close to the domain wall thickness of the hard magnetic component. These requirements have been challenged in many magnetic systems. In this work, various types of mechanical milling are used to study their influence on the composition, microstructure and magnetic properties of a commercial SrFe12O19 powder. Possible alteration of Sr-ferrite powder by mechanical milling has also been studied in a presence of soft magnetic phase. We have been investigating the synthesis of hybrid nanocomposites comprising Sr-ferrite and:
1.cryomilled/ball milled Fe0.65Co0.35
2.melt-spun amorphous/nanocrystalline FeCoSiB-based ribbons
Preliminary results (PXD,SEM,VSM) suggest that different milling conditions, differently affect nanocomposites powder properties.


FF-1:IL13  Single Domain SmCo5@Co Exchange-coupled Magnets Prepared from Core/shell Complex/GO Particles
CE YANG¹, LIHUI JIA², SHOUGUO WANG³, CHEN GAO², DAWEI SHI², YANGLONG HOU¹, SONG GAO², ¹Department of Materials Science and Engineering, College of Engineering, Beijing, China; ²College of Chemistry and Molecular Engineering, Peking University, Beijing, China; ³Institute of Physics, Chinese Academy of Sciences, Beijing, China

Nanocomposites containing exchange-coupled soft and hard magnetic phases have been considering as promising materials to fabricate advanced magnets for future high-density power and data storage applications. SmCo5 based magnets with smaller size and larger maximum energy product have been long desired in various fields such as renewable energy technology, electronic industry and aerospace science. However, conventional relatively rough synthetic strategies will lead to either diminished magnetic properties or irregular morphology, which hindered their wide applications. In this article, we present a facile chemical route to prepare 200 nm single domain SmCo5@Co core/shell magnets with coercivity of 20.7 kOe and saturation magnetization of 82 emu/g. We found that the incorporation of GO sheets is responsible for the generation of the unique structure. The single domain SmCo5 core contributes to the large coercivity of the magnets and the exchange-coupled Co shell enhances the magnetization. This method can be further utilized in the synthesis other Sm-Co based exchange-coupled magnets.


FF-1:L14  Magnetic Properties of Cobalt Ferrite Nanoparticles for Permanent Magnets
E. LOTTINI, A. LÓPEZ-ORTEGA, G. CAMPO, E. FANTECHI, C. INNOCENTI, INSTM-Univ. of Florence, Sesto Fiorentino, Italy; C. DE JULIÁN FERNÁNDEZ, IMEM-CNR, Parma, Italy & INSTM; C. SANGREGORIO, ISTM-CNR, Milano, Italy & INSTM

The research of novel permanent magnets based on free rare-earth compounds has attracted considerable interest in the last years. A strategy is to consider nanoparticles (NPs) in which surface effects and the single domain behaviour determine that they should exhibit better hard properties than the corresponding bulk. However, these properties are counterbalanced by the superparamagnetic effect that is often dominant at room temperature. Such problem can be overcome using materials with high anisotropy, one of the most promising examples being Cobalt ferrite.
Here we investigate the structural and magnetic properties of a family of Cobalt ferrite NPs of different sizes and compositions and synthesized by the thermal decomposition method. At low temperature CoFe2O4 NPs present large coercive fields, up to 1.6 T, and remnant ratio of 0.7, hence indicating the materials is a good candidate for permanent magnet applications. Interestingly, NPs with lower cobalt content exhibit even better properties. We will discuss these results considering the influence of the Co/Fe ratio, the inversion degree and the different contributions that can influence the magnetic anisotropy and properties of these nano-oxides.
This research was supported by the FP7 project NANOPYME (Ref. 310516).

 
Session FF-2 - Soft Magnetic Materials

FF-2:IL01  High Bs-FeSiBPCu Nanocrystalline Soft Magnetic Alloys Contributable to Energy-saving
A. MAKINO, Institute for Materials Research, Tohoku University, Sendai, Japan

Fe-rich Fe83.3-86Si1-4B8-10P2-4Cu0.7-1 nanocrystalline soft magnetic alloys prepared by crystallizing an unusual as-quenched nanohetero-amorphous phase including a large amount of extremely small bcc Fe (less than 2-3nm in size)grains exhibit high B of 1.7 -1.8T (at 800 A/m)almost comparable to the commercial oriented silicon steel, along with extremely low W which is 1/2-1/3 smaller than that of the highest-grade oriented silicon steel and about one-order smaller than those of non-oriented silicon steels at maximum flux density of 1.7T. The new FeSiBPCu nanocrystalline materials with lower materials cost due to absence of rare-metals are expected to not only contribute to energy-saving and reduction of CO2 emission through significant reduction in W but also be useful to conserve the Earth's resources and environment.


FF-2:L02  The Influence of Small Mn Additions on Microstructure and Magnetic Properties of Fe-Si-B-P-Cu Glass-coated Submicron Wires
N. LUPU, S. CORODEANU, H. CHIRIAC, National Institute of Research and Development for Technical Physics, Iasi, Romania; P. SHARMA, A. MAKINO, Research and Development Center for Ultra High Efficiency Nano-crystalline Soft Magnetic Material, Tohoku University, Japan

Soft magnetic nanocrystalline materials are playing an increasing role in specific applications, namely energy efficient magnetic devices, power electronics, electrically powered vehicles and nuclear reactors [1].
Here we report on the preparation of Fe85-xMnxSi2B8P4Cu1 (x = 0; 1; 3 at.%) glass-coated submicron wires with metallic nucleus diameter (Φm) of 0.6÷1.2 µm and the glass coating (tg) of 4÷5 µm, with the aim to study the dependence of their magnetic properties on the diameter of the metallic core and structural changes induced by annealing at different temperatures (Ta) (250 to 550C for 30 min.). All samples are magnetically bistable, irrespective of dimensions and structure. The coercive and switching fields are decreasing significantly for the glass-coated submicron wires with additions of Mn. The measurement of the domain wall velocity (velocities of over 1500 m/s are obtained for optimum nanocrystalline structures) offers a more accurate image over the microstructure developed in glass-coated submicron wires than the conventional magnetic measurements (permeability and switching field).
This work was jointly supported by the ARCMG-IMR, Tohoku University and the Romanian NUCLEU Programme (PN 09-43 01 02).
[1] R. Hasegawa, J. Magn. Magn. Mater. 324 (2012) 3555.


FF-2:L03  Influence of Magnetic Field of Super High Frequency on Hysteretic Properties of Soft Magnetic Microwires
A. CHIZHIK, J. GONZALEZ, Universidad del Pais Vasco, UPV/EHU, San Sebastian, Spain; A. STUPAKIEWICZ, A. MAZIEWSKI, University of Bialystok, Bialystok, Poland; A. ZHUKOV, Universidad del Pais Vasco, UPV/EHU, San Sebastian and IKERBASQUE, Bilbao, Spain

The investigation of the hysteretic properties is the important task related the elucidation of the basic mechanisms of magnetization reversal in microwires in the frame of successful application of glass covered amorphous microwires in magnetic sensors using giant magneto-impedance effect. Here we present the results of the study of the magnetization reversal in the microwire in the presence of circular magnetic field of super high frequency (SHF). An electric current with the frequency up to 6 GHz has been applied to the wire to produce circular magnetic field. We studied glass-coated microwire with the nominal composition Co67Fe3.85Ni1.45B11.5Si14.5Mo1.7 (metallic nucleus diameter is 22.4 μm). Magnetic domain imaging has been performed by means of magneto-optical Kerr effect (MOKE) polarizing microscopy. Hysteresis loops were obtained from the magneto-optic intensity as a result of the MOKE images processing. The presence of the SHF field causes the change of the re-magnetization mechanism - the rotation of the magnetization is observed instead of domain walls motion. Also the hysteresis loop has an asymmetric shape that confirms the co-existence of the stable and meta-stable helical magnetic states in the surface of microwires.


FF-2:IL04  New Soft Magnetic Materials for High Efficiency Applications
R. HASEGAWA, Metglas, Inc., Conway, SC, USA

Increasing fossil fuel consumption and its environment impact in light of worldwide population growth are serious problems. It is therefore imperative to develop environmental-friendly energy sources and energy-efficient devices for energy generation and management. Considerable advancement has been made in the energy-efficient power delivery systems by using amorphous magnetic alloys. Recent developments in this area include nanocrystalline alloys with saturation inductions exceeding 1.75 T. In the power management area, the need for efficient energy conversion from solar and wind power has resulted in development of inductors capable of handling great amount of power. Thus modern power electronics requires magnetic properties which have not been utilized on a large scale. In the area of transportation, electric and hybrid vehicles are gaining momentum, where smaller yet powerful magnetic devices are needed. A new area in the energy management is the utilization of magnetocaloric effects in magnetic cooling. In the energy generation area, fast flux reversal in amorphous and nanocrystalline materials has been utilized in induction accelerators for nuclear fusion. An update on the above developments is the subject of the present talk.


FF-2:IL05  Synthesis of Ferrite Magnets with Magnetization over 1 Tesla
JUN DING, Department of Materials Science & Engineering, National University of Singapore, Singapore

Spinel ferrites such as (Mn,Zn)Fe₂O₄ and (Ni,Zn)Fe₂O₄ have been widely used as soft magnets particularly in high-frequency and microwave areas.  Compared to metal-based soft magnets (e.g., Fe-Si and permalloy), spinel ferrites possess high resistivity, which can ensure a low energy loss, particularly for operation at high frequency.  However, low saturation magnetization limits their applications as soft magnets.  Recently, we have successfully fabricated spinel ferrite with magnetization over 1 Tesla.  Assembling of nanoclusters can result in enhanced magnetization, due to reduction of tetrahedral Fe3+, which is antiferromagnetically coupled with the majority magnetic component - octahedral Fe cations.  Using soft X-ray magnetic circular dichroism and X-ray absorption spectroscopies at Fe L_3,2- and O K- edge supported by charge transfer multiplet calculations, we have quantified the crucial role of Fe, O as well as its hybridizations and revealed unambiguously that the giant magnetism is associated with (1) decrease tetrahedral Fe³⁺ cations, (2) increase octahedral Fe cations in high magnetic iron oxide film and (3) strongly electronic coupled of O with octahedral Fe ions. Supported by first-principle calculations, this unusual behaviour is attributed to the native formation of the small-sized (less than 3 nm) nano-crystals in ultrathin film. Through understanding of its fundamental mechanisms, this may open a path for high magnetization with softer as well as for hard ferrites in general.


FF-2:L06  Comprehensive Approach to Broadband Energy Losses in Mn-Zn Ferrites
F. FIORILLO, C. BEATRICE, O. BOTTAUSCIO, Istituto Nazionale di Ricerca Metrologica, Torino, Italy

We present a general approach to magnetic losses in Mn-Zn ferrites and apply it to broadband (DC - 1 GHz) measurements performed on different types of sintered ring samples. The separate contributions of rotations and domain wall displacements to the magnetization process and the associated dissipation mechanisms are recognized and treated under the concept of loss decomposition, where hysteresis, excess, and classical components are separately identified. By investigating the role of sample size, the eddy current losses are singled out and calculated by means of a variational multiscale approach, taking into account the heterogeneous structure of the material. In sufficiently small samples, spin damping becomes the sole relevant dissipation channel. When involving the spin precession inside the moving domain walls, it gives rise to the hysteresis and excess loss components. The frequency dispersion of the domain wall susceptibility, experimentally separated from the rotational susceptibility, is consistent with a relaxation process, with no resonances involved. Beyond a few MHz, only rotations inside the domains survive and the associated losses are described via the Landau-Lifshitz-Gilbert equation for spin dynamics, with distributed effective anisotropy fields.


FF-2:IL07  Field-annealed Soft Magnetic Amorphous and Nanocrystalline Ribbons with Improved Energy Performance
I. SKORVANEK, Institute of Experimental Physics, Slovak Academy of Sciences, Kosice, Slovakia

The continuing interest in Fe-based amorphous and nanocrystalline alloys is motivated mainly due to their ability to combine a high saturation magnetic flux density with good magnetic softness. In order to further optimize the magnetic performance of these alloys it is important to deepen knowledge about the influence of the processing techniques that can be used to tailor their properties for specific applications. One possible way, which can be employed for this purpose, is the thermal processing under the presence of external magnetic field, called also "magnetic annealing". A special attention of our work is devoted to study of the effects of magnetic annealing in order to produce a controllable anisotropy in series of FeCo- and FeNi-based amorphous and nanocrystalline ribbons with different ratios of Fe/Co and Fe/Ni atoms. We show that the heat treatment in longitudinal or transverse magnetic field is very powerful tool to tailor the shape of hysteresis loops and to control the domain structure. Examples of our recent work on the tuning of soft magnetic properties in these materials by thermal processing in external magnetic field (up to 14 T) for energy and sensor applications will be briefly highlighted.


FF-2:L09  The Effect of Compacting Pressure on Power Loss in a SMC
B. SLUSAREK¹, J.SZCZYGLOWSKI², K. CHWASTEK², B. JANKOWSKI¹, ¹Tele and Radio Research Institute, Warsaw, Poland; ²Czestochowa University of Techology, Czestochowa, Poland

Soft Magnetic Composites (SMCs) have gained a lot of attention of the engineering community due to a high potential for applications in magnetic circuits of elecric machines and high-frequency devices as well as the possibility to tailor up their magnetic properties by appropriate processing conditions [1].
The paper focuses on the effect of compacting pressure on the power loss of a commercial SMC produced by Swedish company Hoganas AB [2]. The Somalloy 500 powder has been compacted under different pressures from the range 500-900 MPa. As binding agent the Kenolube compound [2] has been used.
In the full paper loss density in the SMC shall be described in accordance with the Bertotti's loss theory [3].Preliminary results indicate that the dependence power loss versus frequency follows the relationship f^(3/2) in the range 50-3000 Hz, what indicates that loss is localized in the powder grains, and the "classical" loss term due to bulk eddy currents may be neglected in the analysis. Moreover it has been found that it is possible to describe the dependence power loss versus induction with a power law with a constant slope coefficient.
1. H. Shokrollahi et al., Mater. Sci. Eng. B 134 (2006) 41
2. www.hoganas.com
3. G. Bertotti, Hysteresis in magnetism, Academic Press 1988

 
Session FF-3 - Magnetocaloric and Multifunctional Magnetic Materials

FF-3:IL01  Caloric Effects in Ferroic Materials
L. MANOSA, Facultat de Fisica, Universitat de Barcelona, Barcelona, Spain

Many ferroic materials undergo first order phase transitions with an associated large entropy change which confer to these materials giant caloric properties. These giant caloric properties make ferroic materials excellent candidates for environmental friendly solid-state refrigerating devices [1]. Particularly interesting are those materials with strong coupling between degrees of freedom. Their cross-response to external applyied fields opens-up the possibility of inducing more than one caloric effect in a single material by the application of diverse external fields (mechanical, magnetic and electric). In my talk I will present examples of magnetocaloric, elastocaloric, barocaloric and electrocaloric effects for a number of illustrative ferroic materials.
1.- L. Manosa, A. Planes, M. Acet, J. Mater. Chem. A 1 (2013) 4925.


FF-3:L02  Enhancing the Inverse Magnetocaloric Effect by Proper Doping Ni-Co-Mn-Ga(In) Heusler Alloys
S. FABBRICI, MIST-ER Laboratory, Bologna, Italy; F. ALBERTINI, F. BOLZONI, R. CABASSI, IMEM-CNR, Parma, Italy; G. PORCARI, F. CUGINI, M. SOLZI, University of Parma, Parma, Italy; J. KAMARAD, Z. ARNOLD, Institute of Physics - AVCR, Prague, Czech Republic; B. EMRE, S. YUCE, L. MANOSA, A. PLANES, Universitat de Barcelona, Barcelona, Catalonia, Spain

Ni-Mn based Heusler alloys have been extensively studied due to the remarkable properties associated to the martensitic transformation (MT) they display in a wide range of composition; they were also proposed as potential magnetic refrigerants due to very high values of magnetocaloric effect (MCE). Unlike its parent Ni-Mn-Ga alloy, we have shown that the quaternary Ni-Co-Mn-Ga alloy displays a reverse transformation from a very low moment martensite to a high moment ferromagnetic austenite, which is associated to remarkable values of positive magnetic entropy change (inverse MCE), together with high sensitivity of the MT to applied magnetic field or pressure (dT_c/dH and dT_c/dp).
In this contribution we will review our findings on the role of In in the MCE properties of Ni-Co-Mn-Ga alloys: partial substitution of Ga with In allows to independently tune the magnetic and magnetostructural critical temperatures, emphasizing the figures of interest for applications and ultimately achieving high values of adiabatic temperature change (up to 3 K in a 1.8T field span). We will show the MCE characterization both from direct and indirect methods, showing that it is possible to achieve satisfactory convergence of the results if the appropriate experimental approaches are followed.


FF-3:IL03  Shape Memory and Magnetocaloric Materials: "Giant" Effects Induced by Hydrostatic Pressure and Magnetic Field
Z. ARNOLD, J. KAMARAD, J. KASTIL, Institute of Physics, AS CR, Prague, Czech Republic; F. Albertini, IMEM-CNR, Parma, Italy; S. FABBRICI, IMEM-CNR, Parma and MIST E-R Lab. Bologna, Italy; Y. SKOURSKI, Hochfeld-Magnetlabor Dresden, Dresden, Germany

During the last years, the attractive giant magnetoelastic, magnetocaloric and barocaloric effects in the ferromagnetic shape memory Ni2MnX Heusler alloys, X being a group IIIA-VA element, have been intensively studied. These multi-functional materials are suitable for a large variety of energy-related applications thanks to their extraordinary phenomenology arising from the interplay between magnetic and structural degrees of freedom. The alloys exhibit structural transformation between magnetically ordered phases (cubic austenite and tetragonal martensite) that can be driven by temperature, pressure, stress and magnetic field. We present results of a thorough study of the main basic and functional properties of these alloys in the temperature range down to 1.2 K, high magnetic field up to 60 T and under hydrostatic pressure up to 1.2 GPa. The observed giant temperature, field and pressure induced effects in the Mn-rich Co- and In-doped Ni-Mn-Ga alloys reflect the very substantial changes in the electronic structure of the alloys inducing changes in the structural bonding and magnetic exchange interaction. The small effect of both the magnetic field and the hydrostatic pressure on magnetic and structural properties of stoichiometric Ni2MnGa compound in comparison with the significant magneto-structural instability of all the off-stoichiometric compounds in the same external conditions will be discussed.


FF-3:L04  Revealing and Modelling Interactions or Disorder Effects in Magnetocaloric Materials
J.S. AMARAL*, J.N. GONÇALVES, V.S. AMARAL, Departamento de Física e CICECO, Universidade de Aveiro, Aveiro, Portugal; *also at IFIMUP-IN e Departamento de Física e Astronomia da Faculdade de Ciencias da Universidade do Porto, Porto, Portugal

The search for materials for sustainable energy applications as magnetocalorics requires guidance of fundamental approaches that can reveal the main mechanisms involved (e.g. magneto-volume), and convenient prediction of enhanced properties. Moreover, disorder and non-homogeneity effects, intrinsic or associated with processing are a matter of concern.
We present systematic methods to analyze experimental thermodynamic properties data based on scaling properties of mean-field theory to uncover multiple interactions present. Disorder effects (often smoothing) are also simulated and allow their quantitative characterization via distribution functions. Examples of application to several families of magnetocaloric materials with first or second-order phase transitions are presented, establishing suitable interpolation/prediction schemes of magnetocaloric properties on magnetic field, critical temperature and other parameters.
Beyond the limitations of mean-field theories we present results of a complementary approach, combining ab-initio Density Functional Theory modeling and Monte-Carlo simulation of magnetic materials including the dependence of magnetic interactions on structure/chemical composition to predict magnetic behavior and its impact on magnetocaloric performance.


FF-3:IL05  Transition Metal Based Magneto Caloric Materials
E. BRÜCK, H.D. NGUYEN, Z. OU, Y. YIBOLE, L. CARON, L. ZHANG, F. GUILLOU, N. VAN DIJK, Delft Univ. of Technology, Faculty of Applied Sciences, Fundamental Aspects of Materials and Energy, Delft, The Netherlands

Recently, a new class of magnetic refrigerant-materials for room-temperature applications was discovered. These new materials have important advantages over existing magnetic coolants: They exhibit a large magnetocaloric effect (MCE) in conjunction with a magnetic phase-transition of first order. This MCE is, larger than that of Gd metal, which is used in most demonstration refrigerators built to explore the potential of this evolving technology.
An optimized magneto-caloric material can be seen as an extremely efficient converter for energy from the spin sector (magnetization, magnetic field) to phonons (thermal energy) and vice versa. Due to the microscopic quantum nature of the spin system in a solid-state material, and its coupling to the lattice, this energy transfer possesses an inherently high efficiency.
First principle electronic structure calculations on hexagonal MnFe(P,Si) reveal a new form of magnetism: the coexistence of strong and weak magnetism in alternate atomic layers. The weak magnetism of Fe layers is responsible for a strong coupling with the crystal lattice and thus large thermal effects while the strong magnetism in adjacent Mn-layers ensures Curie temperatures high enough to enable operation at and above room temperature.


FF-3:IL06  The Search for New Magnetocaloric Materials
K.G. SANDEMAN, Department of Physics, Blackett Laboratory, Imperial College London, London, UK

The ideal ferroic refrigerant is one that has a composition- and field-dependent phase transition with a large entropy change [1]. I will show how the search for suitable magnetic refrigerants leads to: a survey of novel critical and tricritical material systems [2,3], the development of characterisation tools to study first order phase transitions, and the use of hi-resolution neutron diffraction data as an ideal test of ab initio theories of finite temperature magnetism [4]. I will highlight the importance of tuning magneto-elastic coupling so as to: (a) exploit the full potential of magnetic cooling and (b) minimise the use of rare earth elements in the life cycle of a future magnetic refrigerator.
[1] S. Fähler et al., Adv. Eng. Mater. 14 10-19 (2012).
[2] K.G. Sandeman, Scr. Mater. 67 566-571 (2012)
[3] A. Barcza et al., Phys. Rev. Lett. 104 247202 (2010)
[4] J.B. Staunton et al., Phys. Rev. B 87 060404 (2013)
The research leading to these results has received funding from the European Community's 7th Framework Programme under grant agreement Nos. 214864 (SSEEC) and 310748 (DRREAM).


FF-3:L07  The Magneto-structural Coupling in MnCoGe-based Compounds
L. CARON, N.T. TRUNG, E. BRÜCK, Fundamental Aspects of Materials and Energy, TUDelft, Delft, The Netherlands

The giant magnetocaloric effect (MCE) in MnCoGe-based compounds was originally discovered in Cr substituted and B-interstitial samples[1]. MnCoGe presents a 2nd order magnetic phase transition at 350 K and a TiNiSi to Ni2In structural transition at 470 K. Although initially uncoupled, the transitions can be coupled and tuned through substitutions of various elements which have been reported in the years following the original reports of Trung et al.[1,2].
The role of substitution in this system is to decrease the lattice parameters and to bring magnetic and structural transitions together giving rise to giant MCE's. However, while high entropy changes are frequently observed, metamagnetic transitions are seldom observed. The absence of metamagnetic behavior and the observation of low adiabatic temperature changes raise the question of how well magnetic and crystalline lattices couple.
In this work we compare the effects of physical pressure and chemical substitution to probe the nature of the magnetostructural coupling. With these tools we explain the apparent contracditory magnetocaloric properties observed in MnCoGe-based compounds.
[1] N. T. Trung et al., Appl. Phys. Lett. 96, 162507 (2010).
[2] N. T . Trung et al., Appl. Phys. Lett. 96, 172504 (2010).


FF-3:L08  Detailed Study of New Magnetic Ordering in FeMnP0.75Si0.25
V. HÖGLIN, Y. ANDERSSON, M. SAHLBERG, Department of Chemistry - Angström, Uppsala University, Uppsala, Sweden; P. NORDBLAD, Department of Engineering Sciences, Uppsala University, Uppsala, Sweden; M. HUDL, ICT Materials Physics, KTH Royal Institute of Technology, Kista, Sweden; L. CARON, Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, TUDelft, Delft, The Netherlands; P. Beran, Nuclear Physics Institute, Academy of Sciences of the Czech Republic, Rez, Czech Republic; M.H. SORBY, Physics Department, Institute for Energy Technology, Kjeller, Norway

Compounds in the (Fe,Mn)2(P,Si)-system have been shown to have potential for magnetocaloric applications. Magnetic and crystallographic properties of FeMnP0.75Si0.25 have been investigated by X-ray powder diffraction, neutron powder diffraction and magnetic measurements. The study reveals both ferromagnetic and incommensurate antiferromagnetic ordering at low temperatures in hexagonal Fe2P-type structures. The incommensurate magnetic structure is of sinusoidal type and has never been observed before in the system (Fe,Mn)2(P,Si). The dual magnetic ordering is due to small differences in the unit cell dimensions and the structural ordering. It is shown that the structural and magnetic properties of P rich compounds (x<0.30) in the FeMnP1-xSix-system are very sensitive to minor changes of the composition.


FF-3:L09  Tuning the Phase Transition by Si Substitution in Mn1.25Fe0.70P1-xSix Compounds
XUEFEI MIAO¹, L. CARON¹, P. ROY², N.H. DUNG¹, L. ZHANG^{1, 3}, W.A. KOCKELMANN⁴, R. SMITH⁴, R.A. DE GROOT², N.H. VAN DIJK¹, E. BRÜCK¹, ¹Department of Radiation Science & Technology, Delft University of Technology, The Netherlands; ²Department of Electronic Structure of Materials, Radboud University, The Netherlands; ³BASF Nederland B.V., The Netherlands; ⁴ISIS, Rutherford Appleton Laboratory, UK

Tunable magnetoelastic transitions and giant magnetocaloric properties have been achieved in (Mn,Fe)2P1-xSix compounds.[1] The phase transition is accompanied by changes in the density of states of the Fe/Mn 3d electrons, which is sensitive to its coordination environment. Replacement of P by Si changes the chemical environment around the Fe/Mn atoms due to different valence electron numbers. Besides, the site preference of Si predicted by density functional calculations would further influence the local electronic and magnetic structures.
In the present study, temperature-dependent neutron diffraction is used to monitor the local magnetic moments and interatomic distances as a function of temperature in Mn1.25Fe0.70P1-xSix compounds. A preferred occupation of Si on the 2c site has been experimentally found, confirming our first-principle calculations. The Si substitution-induced variations in the phase transition process are discussed based on interatomic distance, local electronic structure and local magnetic moment.
[1] Dung N. H. et al., Adv. Energy Mater. 1, 1215(2011).


FF-3:L10  Reduction of the Energy Barrier in First Order Magnetocaloric Materials
K. MORRISON, Physics Department, Loughborough University, Loughborough, Leicestershire, UK

Magnetocaloric materials have seen a resurgence of interest as their potential for room temperature solid state refrigeration applications becomes more apparent. Of the various material systems discovered so far, it is undeniable that the majority of promising materials exhibit a first order phase transition that is, unfortunately, often accompanied by a large energy barrier. This energy barrier is disadvantageous as it results in field or temperature hysteresis that decreases the efficiency of the refrigerative cycle. In order to optimise a given material system it is vital to understand the origin of hysteresis and potential routes to minimise it, whilst retaining the associated boost in entropy change. To this end, we will present results from ac microcalorimetry and inelastic neutron scattering to demonstrate the influence of spin fluctuations on the energy barrier in La(Fe,Si)13, a material system that can exhibit a tri-critical point: where the first order phase transition becomes continuous by tuning the Fe:Si ratio, or by increased temperature and magnetic field. The implications of these results will then be compared with other material systems often cited in the literature.


FF-3:L11  Structural and Magnetic Properties of the Ternary Compounds Mn3-xFexSn and Mn2-xFexSn for x range 0 between 1.25
M.R. FELEZ, UNIFESP, Sao José dos Campos, SP, Brazil; F. YOKAICHYIA, LNLS, Campinas, SP, Brazil; A.A. Coelho, UNICAMP, Campinas, SP, Brazil; S. Gama, UNIFESP, Sao José dos Campos, SP, Brazil

Sustainable energy use in our society imply the development of more efficient refrigerators and of devices to use renewable energies. Magnetic refrigerators and thermomagnetic motors for energy conversion can achieve higher efficiencies than their conventional counterparts. Both require materials with high saturation magnetization, Curie temperatures tunable by composition, and cheap materials. This motivated us to study the structural and magnetic properties of the compounds Mn3-xFexSn and Mn2-xFexSn, 0 ≤ x ≤ 1.25. Heat-treated samples of both compounds were analysed using optical and electronic metallography, X-rays diffraction and magnetic measurements. We confirmed that up to x = 1.25 both phases form Fe solid solutions. The saturation magnetization and the Curie temperature show a marked increase for x > 0.5 for the 3:1 phase and for x > 0.75 for the 2:1 phase. These changes in the magnetic properties are accompanied by changes in the crystal structures of both phases, as revealed by the results from Rietveld refinements of the X-rays diffraction data. Curie temperatures increase above room temperature for both compounds as x increases, and this compositional tunning make both compounds very promising for applications in magnetic refrigerators and thermomagnetic motors.


FF-3:L12  Study of Structural and Magnetic Properties of Si-doped MnAs
S. GAMA¹, M. RODRIGUES FELEZ¹, A. DE AGUIAR COELHO², ¹Universidade Federal de Sao Paulo - UNIFESP - Campus Diadema, Brazil; ²Universidade Estadual de Campínas - UNICAMP, Brazil

MnAs is a first order magnetic material, and for this reason has a high magnetocaloric effect. It is convenient also for use in thermomagnetic motors. Its Curie point can be tuned by replacing As for, e.g., Sb. Recently, it has been reported that replacing As by Si, and preparing the compound by mechanical alloying followed by relatively low temperature heat treatment results in a compound with reduced hysteresis and TC increasing with Si content (Cui et al. JALCOMP 479, 189, 2009). We prepared MnAs1-xSix compounds with x = 0,01, 0,03, 0,06 and 0,09 using the conventional process of melting at 1050°C/24h followed by heat-treatment at 800°C/7days. The metallographic, X-rays, electron microscopy and magnetic analyzes show that for x < 0,06 the sample is single phase, with slightly increased TC and hysteresis. For x = 0,06 and 0,09 occurs precipitation of the compound MnSi, indicating that there is a solubility limit for Si. The saturation magnetization, TC and hysteresis remain approximately constant for the Si doping levels inside the solubility limit. These features are in stark contrast with the properties obtained by the mechanical alloying preparation process, indicating the importance of the preparation process to obtain the magnetic properties of the Si-doped compounds.


FF-3:L13  Characterization of Magnetocaloric Effect in the MnFeP1-xAsx Intermetallic Compounds (x=0.40-0.65)
P. WLODARCZYK, L. HAWELEK, A. KOLANO-BURIAN, P. ZACKIEWICZ, M. KAMINSKA, Institute of Non-Ferrous Metals, Gliwice, Poland; A. Chrobak, University of Silesia, Institute of Physics, Katowice, Poland

The series of MnFeP1-xAsx compounds, with x = 0.40, 0.45, 0.50, 0.55, 0.60 and 0.65 were prepared by solid state vacuum sintering technique and subsequent homogenization process. Calorimetric and magnetization results have shown that the temperature values of magnetoelastic transition cover the temperature range from 250 to 360 K. Adiabatic temperature change for the sintered sample have been measured using magneto-calorimeter. The highest temperature change equaled to 1.5 K for the magnetic field change of 1.7 T was reported. Finally, parameters such as magnetic entropy and adiabatic temperature change were compared with MnFePGe type intermetallic compounds.


FF-3:L14  Hall Probe Imaging of Magnetocaloric LaFe13-xSix
E. LOVELL¹, A.M. PEREIRA¹, K. MORRISON², O. GUTFLEISCH³, L.F. COHEN¹, ¹The Blackett Laboratory, Imperial College, London, UK; ²Department of Physics, Loughborough University, Leicestershire, UK; ³Tech Univ Darmstadt, Dept Mat Science, Darmstadt, Germany

LaFe13-xSix system is attractive for solid state magnetic cooling offering large magnetocaloric entropy change, low hysteresis, and tunability of the metamagnetic transition by introduction of interstitial hydrogen or partial substitution on the La or Fe sites. We have previously studied the dynamics of the metamagnetic transition by correlating the sweep rate of the magnetic field with hysteresis of the M-H loop [1]. More recently, long time relaxation of bulk magnetometry as a function of field orientation has been used to analyze the influence of demagnetization on the transition dynamics and the dimensionality of growth for the nucleating phase [2]. However, spatial information concerning the nucleation and growth dynamics in this system has so far been lacking. In order to address this we have taken scanning Hall probe images on LaFe13-xSix samples and compare directly to long time magnetic relaxation.
[1] J. Moore et al, Appl. Phys. Lett. 95, 252504 (2009).
[2] Hitomi Yako et al, IEEE Trans. Mag. 47, 2482 (2011).
Acknowledgement to Funders of our work: FP7-NMP- 310748-2 (Drastically reduced use of rare earths in applications of magnetocalorics DRREAM) and EPSRC EP/G060940/1 Materials for Energy Applications.


FF-3:L15  Magnetic Properties of Severe Plastic Deformed Gd, Nd and Sm Rare-earth Metals
S.V. TASKAEV, V.D. BUCHELNIKOV, D.S. BATAEV, M.N. ULYANOV, Chelyabinsk State University, Chelyabinsk, Russia; V.V. KHOVAYLO, National University of Science and Technology "MISIS", Moscow, Russia; K.P. SKOKOV, TU Darmstadt, Darmstadt, Germany; A.P. PELLENEN, National Research South Ural State University, Chelyabinsk, Russia

This work reports the magnetic properties of thin Gd, Nd and Sm ribbons obtained with the help of severe plastic deformation (SPD) technique. Severe plastic deformation procedures are very interesting for designing novel functional materials. Depending on the degree of deformation, magnetic, structural or thermodynamic properties could be varied in severely deformed materials, especially in thin ribbons of SPD-treated materials.
The interest in this matter is far from being purely academic. A significant depression of magnetic and thermodynamic properties occurs in severely deformed samples of Gd. The reason of such behavior is in a giant magnetic anisotropy induced by SPD. This unexpected phenomena drives to a new thermodynamic and magnetic properties of severely deformed Gd ribbons which are inapplicable for magnetocaloric applications without additional heat treatment procedure. The heat treatment regimes are directly connected with the degree of plastic deformation.
In this work we continue our previous investigations of the SPD on the magnetic properties of 4-f elements, with special accent on magnetic anisotropy.
Authors appreciate RFBR grant 12-07-00676-a for financing this work.


FF-3:L16  On the Magnetic Fluctuations in the Magnetocaloric-effect in Rare-earth Intermetallic Compounds
P. ALVAREZ-ALONSO¹, P. GORRIA², J.A. BLANCO², ¹Departamento de Electricidad y Electrónica, UPV/EHU, Leioa, Spain; ²Departamento de Física, Universidad de Oviedo, Oviedo, Spain

It is nowadays recognized that magnetocaloric materials must display a large adiabatic temperature and/or a large isothermal magnetic entropy (SM) variation under an adiabatic magnetic field change (Gschneidner et al 2005). In addition, it is clear that the shape and behavior of the SM(T) curves can vary notoriously from one material to another depending on the character of the magnetic phase transition. Three main types of shape are possible for SM(T) curves: (i) a sharp and narrow peak near the critical transition temperature, often associated with first-order magnetic phase transitions (Tegus et al 2002); (ii) a table-like shape, i.e., a broad and a flat peak of SM, linked to multiple sequential magnetic phase transitions (Álvarez et al 2011b); and (iii) a caret-like shape characterized by a broad peak related to second-order magnetic phase transitions and/or crystalline electric field (CEF) (Halder et al 2010).
In this contribution we present the results of a theoretical model including both crystal-field and exchange interactions that consider the effect of magnetic fluctuations to evaluate the temperature dependence of the isothermal magnetic entropy changes in second-order ferromagnetic rare-earth-based intermetallic compounds.


FF-3:L17  Enhanced Refrigeration Capacity in RNi2 Polycrystalline Ribbons Fabricated by Melt Spinning
P. GORRIA¹, J.L. SÁNCHEZ LLAMAZARES², P.J. IBARRA-GAYTAN², C.F. SÁNCHEZ-VALDÉS², P. ALVAREZ-ALONSO³, J.A. BLANCO⁴, ¹Departamento de Física, EPI, Universidad de Oviedo, Gijón, Spain; ²División de Materiales Avanzados, IPICYT, San Luis Potosí, Mexico; ³Departamento de Electricidad y Electrónica, Universidad del Páis Vasco, Bilbao, Spain; ⁴Departamento de Física, Facultad de Ciencias, Universidad de Oviedo, Oviedo, Spain

RNi2 bulk alloys (R = rare earth) show large magnetocaloric (MC) effect at low temperatures (T < 80 K). The MC properties of TbNi2 and DyNi2 ribbons fabricated by means of melt spinning have been investigated. We have observed a noticeable enhancement of the refrigerant capacity (≈30%) respect to that exhibited by the parent bulk alloys. The peculiar microstructure discovered in the samples seems to be the responsible for this improvement in the MC response, making these ribbons promising candidates for use in low-temperature magnetic refrigeration applications.
J.L. Sánchez Llamazares, C.F. Sánchez-Valdes, P.J. Ibarra-Gaytan, P. Álvarez, P. Gorria, J.A. Blanco, J. Appl. Phys. 113 (2013) 17A912.
P.J. Ibarra-Gaytan, C.F. Sánchez-Valdes, J.L. Sánchez Llamazares, P. Álvarez, P. Gorria, J.A. Blanco, Appl. Phys. Lett. 103 (2013) 152401.


FF-3:L18  Magnetocaloric Properties of Gd or Nd Substituted La-Ba Manganites
G. TONOZLIS, G. LITSARDAKIS, Aristotle University, Thessaloniki, Greece

In search of La-Ba manganites with improved magnetocaloric properties, we investigate rare earth additions that may reduce Tc without simultaneously deteriorating magnetic entropy change ΔS(M). Two sample series, with Gd or Nd substituting for La in La0.7Ba0.3MnO3 were synthesized by conventional solid state method. The effects of RE addition on the structural, magnetic and magnetocaloric properties were investigated by XRD, SEM and VSM. Samples have a distorted rhombohedral or tetragonal perovskite structure. For 10% substituted samples, specific magnetization at 3T and 50K is 82.8 Am2/kg for Nd and 86.9 Am2/kg for Gd. Samples exhibit a ferromagnetic to paramagnetic transition which is less sharp for those doped with Gd. Transition temperature decreases to 307K for 10% Nd and to 272K for 10% Gd. The magnetic entropy change ΔS(M)max, observed in the vicinity of transition temperature is 3.35 (2.64) J/kg/K and 3.13(2.43) J/kg/K respectively for a field change of 3(2)T. In order to explain the observed temperature dependence of ΔS(M) the Landau theory of second order phase transition has been applied.


FF-3:L19  Direct Adiabatic Temperature Change Measurements in a Series of Modified Gd5Si2Ge2 Alloys
P. PODMILJSAK^{1, 2}, P.J. MCGUINESS^{1, 2}, K. SKOKOV³, O. GUTFLEISCH³, S. KOBE¹, ¹Department for Nanostructured Materials, Jozef Stefan Institute, Ljubljana, Slovenia; ²Center of Excellence NAMASTE, Ljubljana, Ljubljana, Slovenia; ³TU Darmstadt, Darmstadt, Germany

We have studied direct adiabatic temperature change measurements in a series of Gd5Si2Ge2 alloys where we substituted Ge and/or Si with Fe. The measured values differ from the type of substitution. While substituting Ge produces a typical second order magnetic transition (SOMT) response to the adiabatic temperature change measurements, the Si and Si+Ge substitution show a first order magnetic transition (FOMT) response with a shift in the maximum ΔTad depending if the sample was cooled of heated during the measurement. Direct measurements of the adiabatic temperature change ΔTad were performed on a modified Magnetocaloric Measuring Setup (MMS), with a maximum field in a bore center of μ0H = 1.93 T. We achieved a maximum value of 4.0 K at 261 K on cooling for the sample Gd5Si1.97Ge1.97Fe0.06. After cycling through the transition temperature 10 times we see a change in the measured ΔTad. ΔTad increases to 5.1 K at 263 K on cooling. The increase in ΔTad after cycling the sample is explained by tension in the sample, which is slowly released with cycling through the transition points.


FF-3:IL20  Tetragonal Heusler Compounds for Spintronics
C. FELSER, A.K. NAYAK, O. MESHCHERIAKOVA, V. ALIJANI, J. WINTERLIK, G. FECHER, S. OUARDI, S. CHADOV, Max Planck Institute of Chemical Physics for Solids, Dresden, and Johannes Gutenberg University, Mainz, Germany

Heusler compounds are a remarkable class of materials with more than 1,000 members and a wide range of extraordinary multifunctionalities including half-metallic high-temperature ferri- and ferromagnets, multiferroic shape memory alloys, and tunable topological insulators with a high potential for spintronics, energy technologies and magnetocaloric applications. Recent development of efficient spintronic devices is based on the spin transfer torque (STT) phenomenon. In 2007 Mn_3-xGa was identified as a potential electrode for STT applications. In general tetragonal Heusler compounds Mn₂YZ as potential materials for STT applications can be easily designed by positioning the Fermi energy at the van Hove singularity in one of the spin channels. The Mn³⁺ ions in Mn₂YZ cause a Jahn Teller distortion. High calculated magnetic anisotropy energy (MAE) is the sufficient condition for a material with perpendicular magneto-crystalline anisotropy (PMA). Materials with saturation magnetizations (MS) of 0.2 – 4.0 µ_B, high Curie temperatures (T_C) of 380 – 800 K, high spin polarizations, PMA, and required lattice constant matching with MgO can be realized with ferri- or ferromagnetic Heusler-related compounds. Such materials are strongly recommended for the spin transfer torque magnetic random access memory (STT-MRAM) data storage and the spin torque oscillators (STO) for telecommunication. Additional properties can be designed in tetragonal Heusler compounds with three magnetic sublattices. Mn₂PtIn is a tetragonal Heusler compound with a large exchange bias behavior and Mn₂CoAl a spingapless semiconductor. The potential for rare earth free hard magnets will be discussed too.
References:
Benjamin Balke, Gerhard H. Fecher, Jürgen Winterlik, and Claudia Felser, Appl. Phys. Lett. 90 (2007) 152504.
F. Wu, et. al., Appl. Phys. Lett. 2009, 94, 122503.
Jürgen Winterlik, et. al., Adv. Mat. 24 (2012) 6283.
A. K. Nayak, M. Nicklas, C. Shekhar, Y. Skourski, J. Winterlik, and C. Felser, Phys. Rev. Lett. 110 (2013) 127204
S. Ouardi, G. H. Fecher, J. Kübler, and C. Felser, Phys. Rev. Lett. 110 (2013) 100401


FF-3:IL21  Strain-mediated Magnetocaloric and Magnetoelectric Effects in Oxide Heterostructures
X. MOYA, C. DUCATI, L.C. PHILLIPS, W. YAN, M. GHIDINI, M.E. VICKERS, N.D. MATHUR, Department of Materials Science, University of Cambridge, Cambridge, UK; L.E. HUESO, O. HOVORKA, A. BERGER, CIC nanoGUNE Consolider, Donostia, San Sebastian, Spain; F. MACCHEROZZI, S.S. DHESI, Diamond Light Source, Chilton, Didcot, Oxfordshire, UK; A.I. TOVSTOLYTKIN, D.I. PODYALOVSKII, Institute of Magnetism, Kyiv, Ukraine; E. DEFAY, CEA- LETI, Minatec Campus, Grenoble, France

The local magnetic properties of ferromagnetic manganite films grown epitaxially on ferroelectric BaTiO3 substrates can be controlled either electrically via strain, or magnetically via strain mediated feedback. The resulting magnetoelectric and magnetocaloric effects depend dramatically on the strength of electron lattice coupling in the film, as revealed by 2D magnetic maps constructed from photoemission electron microscopy (PEEM) images with x-ray magnetic circular dichroism (XMCD) contrast. For La0.67Sr0.33MnO3 films with relatively weak electron lattice coupling, strain due to thermally driven structural phase transitions in the substrate modifies the local magnetic anisotropy and forces sharp changes in the orientation of the local magnetization, permitting magnetoelectric effects. For films of La0.7Ca0.3MnO3, stronger electron lattice coupling yields coexisting ferromagnetic and paramagnetic phases that may be interconverted by thermally driving phase transitions in the substrate. Magnetic cycling reveals that this interconversion may be driven via strain-mediated feedback to yield reversible changes in film entropy that are as large as the best magnetocaloric materials.


FF-3:L22  Epitaxial Thin Films and Submicron-sized Patterning of Ni-Mn-Ga
P. RANZIERI, S. FABBRICI, L. NASI, F. CASOLI, V. CHIESI, M. CAMPANINI, F. ALBERTINI, IMEM-CNR, Parma, Italy; L. RIGHI, Chemistry Department, Parma University, Parma, Italy; E. VILLA, CNR-IENI, Lecco,  Italy; F. CELEGATO, G. BARRERA, P. TIBERTO, INRIM, Torino, Italy

Thanks to their multi-functional properties, ferromagnetic shape memory alloys are promising materials for the realization of a variety of devices. The realization of thin films has received many attentions in the last years. Epitaxial grown on a suitable substrate allows obtaining well-structured thin films with well-defined microstructure. In this way some of the key properties of these alloys, relevant to the applications can be largely modified. In the present work we present a structural and magnetic investigation of Ni-Mn-Ga thin films of thickness below 200 nm prepared by r.f. sputtering. This alloy has been grown on MgO and on MgO with a chromium buffer layer. We will show how the thickness influences the temperature stability of the martensitic phase, how it can favour different configurations of martensitic variants and what is the effect of an interfacial chromium layer. Structure and morphology have been investigated by X-ray diffraction, high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED), scanning electron microscopy (SEM) and scanning probe microscopy (SPM). Furthermore, we will also present some results on magnetic nanostructures obtained by patterning Ni-Mn-Ga thin films using the nanosphere lithography.


FF-3:L23  Rapidly Quenched Ferromagnetic Shape Memory Ni-Mn-Ga Wires
C. GOMEZ-POLO, J.I. PÉREZ-LANDAZÁBAL, V. RECARTE, V. SÁNCHEZ-ALARCOS, Dpto. Física, Universidad Pública de Navarra, Campus de Arrosadía, Pamplona, Spain; G. BADINI, M. VÁZQUEZ, Instituto de Ciencia de Materiales, CSIC, Madrid, Spain

Ni-Mn-Ga ferromagnetic shape memory alloys (FSMA) in wire form are studied to evaluate its possible real application. Wires, with nominal composition Ni2.10Mn0.98Ga0.92 and diameters ranging from 170 to 200 10-6 m, were obtained by the rotating water bath melt spinning technique. The wide compositional heterogeneity linked to the rapidly quenching process (occurrence of dendritic-like structure) gives rise to a complex and broad martensitic transformation. A high temperature treatment, leading to the recrystallization of the sample is needed to homogenize the alloy and to reduce the martensitic transformation temperature range. The initial as-cast state is characterized by a reduced saturation magnetization state correlated with the structural disorder and high concentration of structural defects. With respect to the technological application of the FSMA wires, the magnetocaloric effect is analysed under different annealing conditions. A simple bending microactuator is also presented, where the actuation mechanism is suitably controlled by the flow a DC electrical current through the FSMA wires.


FF-3:L24  Atomic Layer- and Chemical Vapor- deposition of Multiferroic Er-Fe-O Thin Films
S. VANGELISTA, R. MANTOVAN, C. WIEMER, A. LAMPERTI, G. TALLARIDA, Laboratorio MDM IMM-CNR, Agrate Brianza (MB), Italy; E. CHIKOIDZE, Y. DUMONT, GEMaC, CNRS-Université de Versailles St. Quentin en Yvelines, Versailles Cedex, France; M. FANCIULLI, Laboratorio MDM IMM-CNR, Agrate Brianza (MB), Italy and Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Milano, Italy

R-Fe-O (R=rare earth) compounds show richness of stable phases displaying multifunctional properties. For instance LuFe2O4 is a charge-ordered ferroelectric at RT, with magnetic ordering below 240 K, being a new prototype multiferroic. R3Fe5O12 materials are reported to show huge magnetostriction at low T and are also studied for their magnetocaloric effects. Hexagonal LuFeO3 shows antiferromagnetic order at RT with ferromagnetic properties at low T. Few reports exists on single phase R-Fe-O (R=Er) thin films synthesis and none of them uses atomic layer- and chemical vapor- deposition (ALD, CVD), cost-effective methods suited for conformal depositions of thin films on large areas. We present the Er-Fe-O thin films synthesis through solid-state reaction between Er2O3 and Fe (or Fe2O3) layers grown by ALD and CVD. Through an annealing at 850 °C in air of a sample with 14 nm of Fe (CVD) grown on top of 10 nm Er2O3 (ALD), we obtain ErFeO3 as dominant phase. After a second annealing at 850 °C in N2 a dominant ErFe2O4 phase can be identified.
Detailed characterizations of the samples will be reported by using GIXRD, XRR, AFM and ToF-SIMS. Magnetic properties are evaluated by VSM, CEMS and MFM. The results demonstrate the feasibility to grow different Er-Fe-O phases by chemical methods.

 
Session FF-4 - Magnetic Devices and Components for Energy Applications

FF-4:IL02  Advances in Magnetic Refrigeration Technology
A. KEDOUS-LEBOUC, M. ALMANZA, A.T. RAMINOSOA, J.-P. YONNET, Grenoble Electrical Engineering Laboratory G2Elab, Grenoble Alpes University, CNRS UMR 5269, Saint Martin d’Hères Cedex, France

Magnetic refrigeration at room temperature is a smart and alternative solution to conventional cooling technology, with less energy consumption and friendly environment. It is based on magnetocaloric effect (MCE), an intrinsic property of some magnetic materials which undergo a temperature change when subjected to a varying magnetic field. This thematic really emerged about 15 years ago, following the discovery of giant MCE in new GdSiGe alloys by Gschneidner and Pecharsky from Ames Laboratory and the demonstration of the feasibility of magnetic cooling by Zimm et al from Astronautics. Since, significant research and development advances have been achieved at the fundamental and the practical plane in both materials and systems. They highlighted, in the same way, that magnetic refrigeration is a complex area of research which requires suitable characterization and modeling tools and a global approach from material to application: upscale material product, efficient magnetic source, optimized shape and composition of the regenerator, optimized operating conditions of the AMR cycle. After a presentation of the stakes of magnetic cooling, we discuss the main issues to overcome and the recent developments particularly in Grenoble in the frame of the Interreg France/Switzerland project Frimag and the national ANR project MagCool.


FF-4:IL05  Energy Harvesting by Ferromagnetic Shape Memory Alloy Films
M. KOHL, M. GUELTIG, R. YIN, Karlsruhe Institute of Technology, IMT, Karlsruhe, Germany; M. OHTSUKA, H. MIKI, Tohoku University, IMRAM, Sendai, Japan

Novel miniature energy harvesting devices are currently being developed in order to meet the requirements of low energy consumption in emerging mobile, wearable and implantable systems. A promising approach is the combination of multiferroic materials and microtechnologies. Ferromagnetic shape memory alloys (FSMAs), for instance, show multiple coupling effects of their physical properties as well as large abrupt changes of strain and magnetization near phase transformations, which is of large interest for small scale applications. The presentation gives an overview on material properties, engineering and fabrication of miniature FSMA energy harvesting devices.
One class of devices is designed to harvest vibrational energy by using the stress-induced reorientation of martensite variants and of magnetic moments in a Ni-Mn-Ga single crystalline foil. Laboratory demonstrators show broadband non-resonant operation at a power output of 2.5 mW/cm^3.
Another class of devices are thermal FSMA microgenerators. The thermally induced abrupt change in magnetization may be used to harvest energy in a small temperature window in the order of 10 K. We show that thermal energy can be harvested in a broad temperature range of 100 - 150 K at large frequency of 80 Hz by mechanical up-conversion.


FF-4:IL06  Magnetic Shape Memory (MSM) Devices for Energy Harvesting
K. ULLAKKO, Lappeenranta University of Technology, Savonlinna, Finland

Vibrational energy harvesting has the potential to convert unused environmental energy to useful electric current. Energy harvesting using Magnetic Shape Memory (MSM) materials is a new way to generate electric power from mechanical vibrations. For many applications, electronic devices are desired in places where no electrical energy is available. Magnetic shape memory (MSM) materials offer a novel way to scavenge the energy of ambient motion in order to power sensors and transmitters. The electric energy can be harvested from vehicles, ships, machines, buildings, water, wind, or human power. The principle behind MSM energy harvesters is the giant change in MSM material’s magnetic permeability caused by straining. Electric energy is generated when the path of the magnetic flux is altered by the MSM sample. MSM energy harvesters provide excellent power-output density, and are durable over billions of cycles. This technology is most efficient for vibration amplitudes of 0.01 mm to 5 mm, and frequencies of 10 Hz to 1 kHz. This is a region which is not optimally transduced by other technologies. Piezos are efficient at low vibration amplitudes up to 0.1mm, and electromechanical energy harvesters work best in strain amplitudes over 5 mm. In this study, we present both experimental and theoretical results for electric energy generation using different vibrational amplitudes and frequencies. As an example, it is shown that an MSM sample of one cubic cm can convert mechanical vibrations at 500 Hz into 20 W of electric energy. This is higher than obtained with other power generation methods. Advantages of MSM energy harvesters compared to the current state of the art harvesters are high electric power output per unit volume, easy to adjust design parameters of the energy harvesters to match the requirements of vibration amplitudes, frequencies or output voltages, cost effective due to simple construction and small size, durable (the MSM elements can be loaded 1400 MPa in compression without breaking), and high resistance to humidity


FF-4:L07  Energy Harvesting Device Based on Nanocrystalline Ribbons
H. CHIRIAC, M. TIBU, N. LUPU, T.A. OVARI, National Institute of Research and Development for Technical Physics, Iasi, Romania; I. SKORVANEK, Institute of Experimental Physics, Slovak Academy of Sciences, Kosice, Slovakia

A multilayer core (MC) consisting of magnetic nanocrystalline ribbons was used to build an electromagnetic energy harvesting device with superior output characteristics compared with other energy harvesting prototypes [1,2]. An arrangement of two NdFeB permanent magnets, bound to a nonmagnetic cantilever beam, oscillates in the proximity of the coil surrounding the MC. The periodic changes in the magnetization of the MC are inducing a voltage in the surrounding coil. The harvester output performances depends on the acceleration and frequency spectrum of the vibrations, configuration of the permanent magnets with respect to the multilayer core, number of turns for the surrounding coil, but especially on the magnetic properties of the core. The achieved power density is 45 mW/cm3 at 1 g (resonant frequency 47 Hz) and seems to be among the highest reported in literature. Such an energy harvesting device having embedded wireless microsensors can provide continuous monitoring without using service personnel in dangerous or high risk areas.
This work was supported by the Romanian Ministry of National Education under Contract No. 7-059/2012 (STREAM).
[1] S.P. Beeby et al., J. Micromech. Microeng. 17, 1257 (2007).
[2] L. Wang and F.G. Yuan, Smart Mater. Struct. 17, 055022 (2008).


FF-4:L08  Is the Spin Seebeck Effect a New Route to Explore for Thermoelectrics?
K. MORRISON, A. CARUANA, Physics Department, Loughborough University, Loughborough, Leicestershire, UK

The Seebeck and Peltier effects are generally well understood and can be used to either generate a temperature differential (by applying a voltage), or a voltage (by applying a temperature difference). A potential application of this technology is as a thermoelectric energy generator (TEG), where waste heat can be scavenged to generate electricity. The co-dependance of electric and thermal conductivities, however, limits the efficiency of this process (as indicated by the figure of merit, zT, which is currently limited to values of the order of 1).
The spin Seebeck effect, on the other hand, refers to the recent observation of a spin polarised current when magnetic materials are subjected to a temperature differential. A key feature of this effect is that the electric conductivity can depend on the spin state of the electron, which leads to the suggestion that zT could be further improved. We will present early results of the measurement of the spin Seebeck effect from thin films of Fe3O4 and Co2MnSi with a view to investigate their potential applications as TEGs.
 
 
Poster Presentations

FF:P02  The Heating Effect of Iron Cobalt Magnetic Nanofluids in an Alternating Magnetic Field: Application in Hyperthermia Treatment
A. SHOKUHFAR, S.S.S AFGHAHI, Advanced Materials and Nanotechnology Research Laboratory, Department of Materials Science and Engineering, K.N. Toosi University of Technology, Tehran, Iran

In this research FeCo alloy nanoparticles were prepared by reducing iron (III) chloride hexahydrate and cobalt (II) sulfate heptahydrate with sodium borohydride in water/CTAB/hexanol reverse micelle system. X-ray diffraction, electron microscopy, selected area electron diffraction and energy dispersive analysis indicate the formation of bcc structured iron cobalt alloy. Magnetic property assessment of nanoparticles reveals that some samples are superparamagnetic with other demonstrating ferromagnetic behavior. The inductive properties of the corresponding magnetic fluids including temperature rise and specific absorption rate were determined. Results show that with increasing the nanoparticle size in the single domain size regime the generated heat increases. Finally by comparing the experimental results with that of Stoner-Wohlfarth model and linear response theory the loss mechanisms were discussed and the best sample for magnetic hyperthermia treatment was specified.


FF:P04  Cluster-Spin-Glass Behavior in La0.7Ca0.3MnO3 Nanoparticles
TRAN DANG THANH, THE LONG PHAN, SEONG CHO YU, SUHK KUN OH, Department of Physics, Chungbuk National University, Cheongju, Korea

We have investigated the dc magnetization and ac susceptibility of La_0.7Ca_0.3MnO₃ (LCMO) nanoparticles synthesized by a reactive milling method with milling time of t_m = 8, 12, and 16 hrs. X-ray diffraction and high resolution transmission electron microscopy reveal that the particle-size distribution is quite homogenous, with mean particle size of about 7 nm. Selected area electron diffraction patterns obtained from a single grain show the single-crystalline nature of LCMO nano-grains. Values of saturation magnetization (M_S) determined by fitting the Langevin function to the magnetization curve measured at 5 K decrease from 36.8 emu/g for t_m = 8 hrs to 14.7 emu/g for t_m = 16 hrs. They are much smaller than the value M_S = 97.5 emu/g of a bulk sample. The temperature dependence of saturation magnetization does not follow Bloch's T^3/2 law, but follows a T^ε law with ε increasing from 1.69 to 1.76 as the milling time increases from 8 to 16 hrs. A slightly greater value of ε compared to the bulk value is due to the effect related to small particle sizes. The dc magnetization, ac susceptibility, and fitting results indicate the existence of the cluster-spin-glass phenomenon in the samples, which originates from the competition between FM and AFM interactions.


FF:P05  Magnetocaloric Properties of Gd-Ge-Si Alloys Modified with Iron
J. FERENC, M. KOWALCZYK, G. CIESLAK, T. ERENC-SEDZIAK, T. KULIK, Faculty of Materials Science and Engineering, Warsaw University of Technology, Warsaw, Poland

Magnetocaloric substances are promising materials for application in more energy efficient cooling devices. One of interesting material groups are alloys containing gadolinium, germanium and iron modified with other elements. In addition modification of material's production techniques gives opportunity to get material with uneven properties.
The influence of annealing of Gd5Ge2Si2Fex alloys at 1200°C and doping with various amount of iron on structure as well as thermal and magnetocaloric properties is investigated. Distribution of alloying elements was investigated by SEM/EDS technique.
It was discovered that heat treatment up to 10 hours improves the entropy change, but reduces the temperature of maximum magnetocaloric effect by up to 50 K. Extensive annealing reduces Gd5Ge2Si2 phase content which, in turn, limits the entropy change. Addition of iron to the generic alloy enhances the magnetocaloric effect. It is strongly visible for x = 0.4 - 0.6, especially in combination with annealing at 1200°C. In this case, entropy change for magnetic field from 0 to 2 T increases from 3.5 to 11 J/kgK, and the temperature of maximum magnetocaloric effect drops to 250 K.


FF:P06  Internal Friction in Superelastic FeMnAlNi Alloys
V.V. KHOVAYLO, I.S. GOLOVIN, National University of Science and Technology "MIS&S", Moscow, Russia; T. OMORI, R. KAINUMA, Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai, Japan

Recently, it has been found that FeMnAl-based ferrous alloys demonstrate well-defined superelastic properties in a wide range of temperature. The uniqueness of these materials is a weak dependence of the superelastic stress on temperature which is thought to originate from a small transformation entropy change [T. Omori, et. al, Science 333 (2011) 68].
Here we report on internal friction in these materials. The internal friction was studied by a Dynamic Mechanical Analysis (DMA) instrument at different frequencies of external load and at temperatures up to 473 K. Experimental results obtained for Fe43.5Mn34Al15Ni7.5 samples showed that internal friction in a sample quenched from 1473 K and in a sample subjected to the subsequent aging at 473 K for 6 h is essentially the same. In both the samples, internal friction drastically increases when the deformation exceeds 0.1%. This increase is due to the stress induced martensitic transformation.


FF:P10  The Magnetocaloric Effect of GdFe1-xCoxSi Compounds
P. ZACKIEWICZ, L. HAWELEK, P. WLODARCZYK, M. KAMINSKA, A. KOLANO-BURIAN, Institute of Non-Ferrous Metals, Materials Science Department, Laboratory of Advanced Magnetic Materials, Gliwice, Poland; A. CHROBAK, University of Silesia, Institute of Physics, Katowice, Poland

In this work we report the magnetic and magnetocaloric properties of GdFe1-xCoxSi compounds with x = 0, 0.1, ., 1 . All samples were prepared from pure elements (Gd - 99.9 wt%, Fe - 99.99 wt%, Co - 99.99 wt%, Si - 99.999 wt%) by arc melting technique. The structure and microstructure were studied using the RAPID D/MAX II type Rigaku Denki X-ray diffractometer and the JEOL X-ray microanalyzer, respectively. The magnetocaloric effect measurements were performed by applaying direct (adiabatic temperature change measurements) and indirect (magnetization measurements) methods. The maximum value of the adiabatic temperature change was found near 128 K as ΔT = 1.05 K for an applied field of 1 T.
Such obtained values are consistent with the previous results presented by Napoletano [1] and Qin [2].
[1]. M. Napoletano, F. Canepa, P. Manfrinetti and F. Merlo, J. Mater. Chem., 2000, 10, 1663-1665
[2]. W.D. Qin et al. / Journal of Alloys and Compounds 265 (1998) 26 -28


FF:P11  Entropy Change Calculations for Pure Gd and a Ni-Mn-Cu-Ga Heusler Alloy: Constant Field vs. Constant Temperature Experiment
J. FERENC, M. KOWALCZYK, R. WRÓBLEWSKI, G. CIESLAK, K. SIELICKI, M. LEONOWICZ, T. KULIK, Faculty of Materials Science and Engineering, Warsaw University of Technology, Warsaw, Poland

Magnitude of the magnetocaloric effect may be described by entropy change calculated from the dependence of magnetization (M) on temperature (T) and magnetic field strength (H). To calculate the entropy change, it is necessary to have a 3 dimensional plot where abscissa axes are T and H, and ordinate axis is M. There are two ways to obtain such 3D graph, (i) measurement of M vs. T at constant H (thermomagnetic curves), and (ii) isothermal measurement of M vs. H for different T values. For accurate calculations, large number of data points is needed, but this requires long acquisition time. Reduction of data points may lead to inaccurate results. Question arises, which method (const. T or const. H) should be used, and how little data points are needed to keep the results reliable.
In this work, gadolinium and a Ni-Mn-Cu-Ga Heusler alloy were studied. For both materials, calculations of entropy change were done from the measurements executed in const. T and const. H modes, with gradually reduced number of data points (by increasing T and H interval, respectively). The calculations showed that for both materials, the calculation of entropy change based on M = f(T) with H = const, with only 6 field strength values, is sufficiently accurate, and the error is less than 5%.


FF:P16  Phase Diagram of Ni50Mn35In15 Heusler Alloy with Exchange Inversion
M.A. ZAGREBIN, National Research South Ural State University, Chelyabinsk, Russia, Chelyabinsk State University, Chelyabinsk, Russia; V.D. BUCHELNIKOV, K.I. KOSTROMITIN, Chelyabinsk State University, Chelyabinsk, Russia

Recent experiments have shown that in some Ni-Mn-In Heusler alloys there are three magnetic phase transitions in the austenite and martensite and coupled magnetostructural transition during cooling [1]. Such behavior was described by the Ginzburg-Landau theory in [2]. It was shown that the paramagnetic cubic (PMC)-ferromagnetic cubic (FMC) phase transition, FMC-PM tetragonal (PMT) one, and PMT-FM tetragonal (FMT) one can occur. In the recent work another sequence of phase transitions for Ni50Mn35In15 has been proposed by Bennett et al. [3], namely, the PMC-FMT phase transition and FMT - ferrimagnetic tetragonal (FRMT) one. In this work with the help of the Ginzburg-Landau theory new phase diagrams of Ni50Mn35In15 alloy are investigated. We consider the case when the magnetizations of sublattices are not equal. In this case minimizations of functional with respect to the order parameters give us eight equilibrium states PMC, PMT, FMC, FMT, anti-FM cubic (AFMC), AFMT, FRMC and FRMT phases. The proposed phase diagram allows us to explain experimental phase transitions in Ni50Mn35In15 alloy qualitatively [3].
[1] T. Krenke et al, Phys. Rev. B. 73, 174413 (2006).
[2] V.D. Buchelnikov et al. JMMM. 320, e175 (2008).
[3] L.H. Bennett et al. J. Alloys and Comp. 525, 34 (2012).


FF:P17  Synthesis and Magnetism in Fe5(Si,P)B2
J. CEDERVALL, M. SAHLBERG, Department of Chemistry - The Angstrom Laboratory, Uppsala University, Uppsala, Sweden

In the high power consumption of today reliable renewable energy production is necessary for a sustainable environment. This includes power production from, for example, wind power plants. In the generators of windmills permanent magnets are used to transfer kinetic energy to electricity. The best magnet for this application today is an alloy of neodymium, iron and boron. Neodymium is an element that has both high and unstable prize as well as environmentally unclean mining and manufacturing processes. This is why the importance of rare earth free permanent magnets will rise. Therefore rare earth free alloys with high Curie temperature, high saturation magnetization and high energy product are currently searched for.
In this project, iron rich ferromagnetic compounds Fe5SiB2 and Fe5PB2 have been studied. The synthesis of the compounds was done via a combination of arc melting, drop synthesis and subsequent heat treatment. The crystal structure has been characterized with X-ray diffraction and the magnetic properties with a SQUID magnetometer. The materials crystallize in the Cr5B3-type structure (I4/mcm). Magnetic measurements show Curie temperatures well above room temperature (784K for Fe5SiB2) and saturation magnetization comparable to the neodymium magnets.


FF:P18  Microencapsulation Process of Intermetallic Compounds with Sn for Applications in Magnetic Refrigerators and Thermomagnetic Motors
C.S. FRANCISCO, S. GAMA, M.R. FELEZ, R.A.G. SILVA, Departamento de Ciencias Exatas e da Terra, UNIFESP - Diadema, SP, Brazil

Magnetic refrigerators and thermomagnetic motors are important devices applied to energy economy and conversion of renewable energies. Both devices require materials with appropriate mechanical and magnetic properties. Usually, these materials are intermetallic compounds, brittle and fragile. In order to have them in shapes appropriate to the devices, it is necessary to process them by powder metallurgy. A convenient process is to sinter at low temperatures after microencapsulating them into low melting point materials. We are developing Mn-rich intermetallic compounds for magnetic refrigerators and thermomagnetic motors for low temperature hot sources, and developed a microencapsulation technique to sinter them at low temperature. The encapsulation process consists of chemically deposit a layer of Cu followed by deposition of Sn on the powdered compounds, in a process that allows the control of the Sn layer thickness. The process requires adaptations depending on the Mn content of the compounds. The encapsulated powders were characterized by metallographic, X-rays and magnetic analyzes, that confirm the preservation of the magnetic properties after the deposition. Pressed and low temperature sintered powders of the compounds also preserve the original magnetic properties.