Future Perspectives on Novel Magnetic Materials

Santorini Palace Hotel, Santorini, May 29-June 3, 2018





Hour Event
2:00-5:30 pm INAPEM
5:30-7:00 pm WELCOMING RECEPTION
Hour Event
Symposium 8:30 am-9:15 am Stuart Parkin
9:15 am-10:00 am Claudia Felser
10:00 am- 10:30 am COFFEE BREAK
10:30 am-11:15 am Oliver Gutfleisch Heavy rare earth free, free rare earth and rare earth free magnets – vision and reality

It is commonly understood that among the intermetallic phases used for permanent magnets, practically none can fully realize its potential based on the intrinsic magnetic properties. We discuss different reasons leading to this limitation, known as the Brown paradox, and discuss some possible ways of overcoming it. We look into Dy- and Tb-less grain boundary diffused magnets and the scope for the complete elimination of the heavy rare earth elements. Then we compare the intrinsic magnetic properties of (Nd1-xCex)2(Fe1-yCoy)14B single crystals with the extrinsic characteristics of sintered and hot compacted magnets, so called rare earth balance magnets, made from the very same alloys. Finally, assessing RE-free materials, our results obtained on Mn- and Co-based RE-free single crystals are compared with the hard magnetic properties of Mn-based permanent magnets.
Spintronics 11:15 am-12:00 am Bernd Rellinghaus Quantitative Mapping of Spin Textures in a Transmission Electron Microscope

Besides their inherently small size, magnetic nanostructures exhibit to an increasing extend complex spin textures that vary at the atomic length scale. Accordingly, ultra-high resolution techniques are required in order to unveil and quantify these spin textures in three dimensions. The talk reviews in examples state-of-the-art magnetic characterization techniques as provided by modern transmission electron microscopy.
Skyrmions [1] are topologically non-trivial vortex-like spin textures that are envisioned to be soon utilized for spintronic applications [2]. Knowledge about the full three-dimensional spin texture is of particular importance here. A combination of inline and off-axis electron holography (EH) is used to quantitatively reconstruct the projected in-plane magnetic field pertaining to both the helical and the skyrmion lattice phase of chiral magnet Fe0.95Co0.05Ge. In combination with electron tomography and by magnetostatic simulations it is shown, that (i) the amplitude of the projected in-plane magnetic induction is too small to originate from homogeneous Bloch Skyrmions extending throughout the thickness of the magnetic layer and that (ii) the underlying spin textures are rather modulated in all three dimensions [3].
It is further highlighted that electron magnetic chiral dichroism (EMCD), which – complementary to the above approaches – probes the out-of-plane component of the magnetic induction, promises to allow for atomic resolution magnetic characterization upon combining it with local probe techniques such as, e.g., electron vortex beams [4].
[1] A. N. Bogdanov and A. Hubert, J. Magn. Magn. Mater. 138 (1994) 255.
[2] N. Nagaosa and Y. Tokura, Nature Nanotechnology 8 (2013) 899.
[3] S. Schneider et al., Phys. Rev. Lett. (2018), in print.
[4] D. Pohl et al., Scientific Reports 7 (2017) 934.
12:00 am-12:35 pm Christian Back Spin orbit fields at the Fe/GaAs(001) interface

Interfacial spin-orbit fields (SOFs) enable the manipulation of the magnetization through an in-plane charge current. Besides technological interest, the intricate processes involved in spin to charge conversion at interfaces have provoked theoretical and experimental efforts to disentangle the underlying mechanisms. Here we study a particularly simple single crystalline interface, Fe/GaAs(001). The structural and magnetic properties of this particular interface are well understood [1] and we have used it to demonstrate various effects related to interfacial spin orbit fields.
First of we demonstrate crystalline anisotropic magneto-resistance showing C2v symmetry [2], second we show anisotropic magneto-optic response [3]. Finally, we use ferromagnetic resonance based methods to investigate interfacial SOFs [4] and anisotropic damping [5]. We report the observation of robust SOFs occuring at a single crystalline Fe/ GaAs (001) interface at room temperature. We find that the magnitude of the interfacial SOF, caused by the reduced symmetry at the interface, is about as strong as in ferromagnetic metal/non-magnetic metal systems. The large spin-orbit fields at the interface also enable spin-to-charge current conversion at the interface, known as spin-galvanic effect [4]. Our results also demonstrate that single crystalline Fe/GaAs interfaces may enable efficient electrical magnetization manipulation
References:
[1] M. Gmitra et al., Phys. Rev. Lett. 111, 036603 (2013)
[2] T. Hupfauer et al., Nat. Commun. 6, 7374 (2015)
[3] M. Buchner et al., Phys. Rev. Lett. 117, 157202 (2016)
[4] L. Chen et al. Nat. Commun. 7, 13802 (2016)
[5] L. Chen et al., Nat. Phys., 10.1038/s41567-018-0053-8 (2018)
12:35 pm-1:10 pm Yoshi Tokura Exploring Exotic Magnets with Large Topological Hall Effect

Berry curvature arising from the Weyl fermions and/or the real-space scalar spin chirality can give rise to the action of effective magnetic field on the conduction electrons and hence produce the topological Hall effect. Furthermore, their temporal dynamics can also cause versatile emergent phenomena, including nonreciprocal transport, enhanced carrier scattering, thermoelectric effect, etc. Here, taking the examples of cubic chiral magnets, frustrated triangular- or Kagome-lattice magnets and magnetic topological insulators, we report the experimental attempts to design and maximize the emergent magnetic-field effects with possible applications to spintronic functions.
1:10 pm-3:30 pm LUNCH BREAK
3:30 pm-4:05 pm Nikolic Branislav Spin and Charge Pumping by Current-Driven Domain Wall Motion and Annihilation

This talk introduces recently developed [1] multiscale and self-consistent framework which combines time-dependent nonequilibrium Green function (TD-NEGF) algorithm, scaling linearly in the number of time steps and describing quantum-mechanically conduction electrons in the presence of time-dependent fields of arbitrary strength or frequency, with classical description of the dynamics of local magnetic moments based on the Landau-Lifshitz-Gilbert (LLG) equation. Such TD-NEGF+LLG approach can be applied to a variety of problems where current-driven spin torque induces the dynamics of magnetic moments as the key resource for next generation spintronics. Previous approaches for describing such nonequilibrium many-body system have neglected noncommutativity of quantum Hamiltonian of conduction electrons at different times and, therefore, the impact of time-dependent magnetic moments on electrons which can lead to pumping of spin and charge currents that, in turn, can self-consistently affect the dynamics of magnetic moments themselves. Using magnetic domain wall (DW) as an example, we predict that its motion will pump time-dependent spin and charge currents, on the top of injected DC currents driving the DW motion, where conversion of spin currents into AC voltage via the inverse spin Hall effect offers a tool to precisely track the DW position along magnetic nanowire. We also quantify the DW inertial displacement due to its acceleration and deceleration by pulse current, as well as the entailed spin and charge pumping. Finally, motivated by the recent experiments where two DWs of opposite topological charge are collided and annihilated to create a burst of spin waves [2], we discuss additional signatures of this phenomenon as the burst of spin and charge currents.
4:05 pm-4:40 pm Christian Pfleider Energetics of Skyrmions in Chiral Magnets

Skyrmions in chiral magnets and related topological spin textures attract great interest as a possible route towards novel spintronics devices. A series of studies is reported of the mechanisms controlling the stability of skyrmions in chiral magnets for different temperature versus field histories. The character of magnetic textures, notably as observed in bulk compounds, at surfaces and in thin epitaxial films will be addressed.
4:40 pm-5:20 pm Michalis Charilaou Monopole-induced emergent electric fields in ferromagnetic nanowires

Magnetization processes may become surprisingly elaborate as dimensions become comparable to fundamental magnetic length scales. Conventional wisdom associates magnetization reversal in cylindrical nanoparticles with curling-type processes, but these considerations neglect the global topological constraints which preclude complete reversal via continuous processes. In this talk, I will show that the irreversibility of the magnetization process in nanowires, made from simple ferromagnetic materials, is directly linked to the pair-creation of topological point defects in the form of hedgehog-antihedgehog pairs, whose subsequent separation accomplishes the complete reversal of the magnetization. These fast moving hedgehogs produce an emergent electric field with unprecedented magnitude and solenoidal character, in analogy to the magnetic field of a moving electric charge, thus providing striking evidence that a moving hedgehog constitutes an emergent magnetic monopole.
5:20 pm-5:50 pm Michael Coey
5:50 pm-7:00 pm DISCUSSIONS/POSTERS
Hour Event
Spintronics/Topological 8:30 am-9:45 am Albert Fert Topology and Spin-Orbit Coupling in Low Dimensions For Novel Directions in Spintronics (from spin/charge conversion to skyrmions)

The appearance of new phenomena induced by spin-orbit coupling (SOC) and topology effects at surfaces, interfaces and low dimension materials has led to the emergence of novel directions in spintronics. I will describe some of these and their potential for spintronic devices [1].
The electron states at surfaces or interfaces of topological insulators, Rashba interfaces and some interfaces between oxides are characterized by a locking between the spin and momentum degrees of freedom. Thanks to the Edelstein and Inverse Edelstein Effects, this locking can be exploited for very efficient conversions between spin and charge currents (which, parenthetically, is the basic function in any spintronic device). Promising similar effects are obtained in 2D materials with large SOC as, for example, ultra-thin films of Transition Metal Dichalcogenides (TMD) or heterostructures associating 2D materials.
Second example, the chiral spin interactions (Dzyaloshinskii-Moriya interactions) induced by SOC at the interface of a magnetic film with a heavy metal can be used to create skyrmions, nanoscale spin whirls that are stabilized by their topology. The recent results in several groups on the electrical creation, manipulation and detection of skyrmions at room temperature in magnetic multilayers represent real advances on the route to applications.
[1] Example of recent review: A. Soumyanarayanan, N. Reyren, A. Fert and C. Panagopoulos, Nature 539, 509 (2016).
9:45 am-10:30 am Theo Raising All Optical control of magnetic order: new developments

The manipulation of magnetism by ultrashort laser pulses is a fundamentally challenging research area with a potentially high impact for energy efficient data storage. In ferrimagnets, fs-laser induced switching appears to go via a highly non-equilibrium state, exploiting the antiferromagnetic exchange interaction between sub-lattices. Fs-Xray experiments and atomistic simulations reveal the importance of nanoscale chemical and magnetic inhomogeneities for non-local transfer of angular momentum. New, engineered multilayer and dielectric materials appear to offer new opportunities for highly efficient manipulation of magnetic order..
10:30 am- 11:00 am COFFEE BREAK
11:00 am-11:35 am Jairo Sinova Topological Antiferromagnetic Spin-orbitronics

Antiferromagnetic spintronics considers the active manipulation of the antiferromagnetic order parameter in spin-based devices. An additional concept that has emerged is that antiferromagnets provide a unifying platform for realizing synergies among three prominent fields of contemporary condensed matter physics: Dirac quasiparticles and topological phases. Here spintronic devices made of antiferromagnets with their unique symmetries will allow us to control the emergence and to study the properties of Dirac/Weyl fermion topological phases that are otherwise principally immune against external stimuli. In return, the resulting topological magneto-transport phenomena open the prospect of new, highly efficient means for operating the antiferromagnetic memory-logic devices. We discuss how these topological phases emerge and how their robustness depends on the relative orientation of the Neel order parameter that can be manipulated by Neel spin-orbit torques. Their natural excitations are in the THz but with the additional consideration that they can now be directly tuned
11:35 am-12:10 am Suchitra Sebastian
12:10 am-12:40 pm Chistoforos Moutafis Magnetic Skyrmions: Statics And Dynamics
12:40 pm-2:00 pm DISCUSSIONS/POSTERS
2:00 pm-4:00 pm LUNCH BREAK
New Compounds by DFT 4:00 pm-4:30 pm Christian Elsäesser Search for substitutes of hard-magnetic materials containing less critical elements by computational high-throughput screening

The discovery and design of new hard-magnetic intermetallic phases for permanent magnets are addressed by means of an efficient and predictive computational high-throughput screening (HTS) approach. The challenge is to identify substitutes for established hard-magnetic materials like Nd2Fe14B, which have similarly good magnetic properties but less constraining resource criticalities. To find promising candidates for new hard-magnetic phases, combinatorial HTS calculations based on density functional theory (DFT) are carried out to search for crystal structures and chemical compositions of intermetallic phases composed of transition-metal, rare-earth, and other substitutional or interstitial alloying elements, which have comparably good intrinsic ferromagnetic properties but contain less amounts of critical rare-earth elements than, e.g., Nd2Fe14B.
4:30 pm-5:00 pm Takashi Miyaki A combined computational and machine-learning study of rare-earth-lean magnet compounds

RFe12-type compounds are attracting renewed interest as possible strong permanent magnet compounds because of their high iron content. Recently synthesized NdFe12Nx film shows higher saturation magnetization and anisotropy field than Nd2Fe14B, although its bulk phase is thermodynamically unstable. I will present first-principles study on the effect of chemical substitution on magnetism and structural stability. I will also discuss how machine learning accelerates magnetic-materials discovery. Application to RFe12-type compounds shows that Bayesian optimization offers an efficient method to find optimal chemical composition. Kernel method using orbital-field matrix as a descriptor reproduces the magnetic moment and formation energy of thousands of transition-metal compounds in reasonable accuracy, which can be utilized for virtual screening of new magnetic compounds.
5:00 pm-5:30 pm George Hadjipanayis Prospects for the Development of Rare Earth-Free/Lean Permanent Magnets
5:30 pm-6:00 pm Sergiu Arapan Searching for the rare-earth free permanent magnets with structure predicting methods: possibilities and limitations.

Structure prediction based on evolutionary/genetic algorithm methods combined with density functional theory calculations provides material scientists with a tool to predict from scratch the stable structure of a compound just with the mere knowledge of its composition. In practice, however, there are many factors that make the process of predicting a new structure by simulations as hard as obtaining it in the lab. Here I will present some result of searching for new rare-earth free magnetic structures by using the evolutionary code USPEX and ab-initio code VASP, which me and my colleague Pablo Nieves obtained during participation in the NOVAMAG project. Based on this experience, I will bring into discussion the limitations as well as the possibilities for making the best use of structure predicting methods.
6:00 pm-6:30 pm Herper Heike How to improve the intrinsic magnetic properties of REFe12-xZx magnets

The steadily growing usage of ‘green energies’, e.g. in electric transportation comes along with an increasing demand for new high performance magnets preferably based on cheap, abundant and, non-critical raw materials but with a performance comparable to commercial Nd-Fe-B magnets. As a possible alternative to existing commercial magnets, tetragonal NdFe11M (1:12) phases are discussed. However, the stabilizing nonmagnetic element M (e.g. Ti, V, Mo) reduces the magnetic performance and its concentration should be as small as possible. Here we present a systematic study for a series of (RE1-xYx)Fe12-zMz phases with M being a nonmagnetic transition metal atom such as Ti or V, and RE = Nd, Sm using state of the art density functional theory methods. Aiming to improve the magnetic properties (reduce z) and to reduce the RE concentrations (increase x) the phase stability has been studied for varying x and z. Stable phases have been magnetically characterized in detail. Showing that e.g. a partial replacement of Nd by Y leads to an uniaxial anisotropy even at low temperatures, e.g. K1 = 1.3 MJ/m3 for NdYFe11Ti without nitrogenation. Our results show further that for the whole concentration range of x the 1:12 is stable down to approximately z=0.5 for Ti which leads to an increase of the magnetization by 17%.
In this study the geometry has been optimized using the VASP (PBE) code with PAW potentials whereby the 4f electrons of Nd and Sm were treated as core electrons. Calculations have been performed for super-cells with up to 52 atoms. For the magnetic characterization the optimized structures were transferred to the full potential LMTO code RSPt treating the 4f electrons within the GGA+U formalism.
This work is supported by the European Research Project NOVAMAG (EU686056) and STandUP for energy (Sweden).
6:30 pm-7:00 pm Michael Farle Shell Ferromagnetism: a pathway for hard magnets with “monopole” characteristics?
7:00 pm-7:30 pm DISCUSSIONS
Hour Event
Micromagnetics 8:30 am-9:00 am Thomas Schrefl Activation volume and structural defects in permanent magnets

The coercive field of permanent magnets is lower than its anisotropy field. This reduction has to be attributed to structural defects and thermal activation. We compute the activation volume for different type of magnets using micromagnetic simulations. Thus, a relation between the magnet’s microstructure and the activation volume can be established. In NdFeB magnets, the activation volume increases from (4.3 nm)³ for an ideal structure without any defects to (7.9 nm)³ for a nanocrystalline magnet with ferromagnetic grain boundary phases. This change of activation volume with microstructure has an unwanted consequence: As one approaches ideal microstructures, the drop in coercivity due to defects is reduced but the drop due to thermal activation is increased.
Work supported by EU H2020 project Novamag (Grant no 686056).
9:00 am-9:30 am Josef Fidler More than three decades of research on REPM: Are further improvements to be expected in the future?

Computational micromagnetism leads to a deeper understanding of hysteresis effects by the visualization of the magnetization reversal processes of newly developed hard magnetic materials. The search for suitable magnetic materials, crystal structures and their expected hard magnetic properties as replacement for rare earth containing permanent magnets is of great economical and scientific interest. A novel approach of combining high resolution nanoanalytical characterization with finite element micromagnetic modelling has been demonstrated [1,2]. The limits for the coercive field in nucleation-controlled Nd-Fe-B based magnets with a high energy density product (B.H)max beyond 450 kJ/m3 will be discussed. The increasing demand of high-performance rare earth permanent magnets in automotive and energy conversion applications led to the search and development of heavy rare earth lean RE2Fe14B based or rare earth free magnets and to the optimization of the complex multiphase microstructure of the magnets. The aim of the presentation is to discuss the potential of alternative materials for a further improvement of the coercive field together with the energy density product based on the reported magnetic saturation polarization and magnetocrystalline anisotropy values and optimized microstructures.
[1] G. A. Zickler, J. Fidler, J. Bernardi, T. Schrefl and A. Asali,
A combined TEM/STEM and micromagnetic study of the anisotropic nature of grain boundaries and coercivity in Nd-Fe-B magnets,
Advances in Materials Science and Engineering, Volume 2017, Article ID 6412042, 12 pages, (2017), https://doi.org/10.1155/2017/6412042.
[2] G. A. Zickler, J. Fidler,
Nanocompositional electron microscopic analysis and role of grain boundary phase of isotropically oriented Nd-Fe-B magnets,
Advances in Materials Science and Engineering, Volume 2017, Article ID 1461835, 17 pages, (2017), https://doi.org/10.1155/2017/1461835.
9:30 am-10:00 am Hiroki Tsuchiura : Theoretical studies on the magnetic properties of Sm(Fe_{1-x}Co_{x})_{12} and Pr(Fe_{1-x}V{x})_{12} systems.

Recently, there has been renewed interest in rare-earth based magnetic materials RFe12 as possible candidate novel strong permanent magnetic materials. In this talk, we will discuss the magnetic properties Sm(Fe1-xCox)12 and Pr(Fe1-xVx)12N using effective spin models based on the information obtained by first-principles calculations.
10:00 am-10:30 am COFFEE BREAK
R-free/lean magnets Experimental
10:30 am-11:00 am Laura Lewis Chimera or not? Updates on L10 FeNi

Despite mixed messages in North America, global supply and demand uncertainties continue to motivate the development of new types of sustainable, ecologically friendly and accessible advanced permanent magnets. As chemically ordered L10-type FeNi (aka tetrataenite) has been confirmed in meteoritic materials to exhibit a theoretical magnetic energy product exceeding (BH)max = 335 kJ/m3 (42 MGOe); protocols to synthesize this phase in industrially relevant timescales remain of high interest. Recent results concerning the development of chemical order and tetragonality in synthetic FeNi will be discussed, with contemplated routes to accelerated phase formation presented for Workshop consideration and feedback.
This work is supported by the NSF under Grant Number Grant # 1601895.
11:00 am-11:30 am Dagmar Goll BULK HIGH-THROUGHPUT EXPERIMENTATION TO DISCOVER NEW PERMANENT MAGNETS

Novel magnet materials filling the gap between hard ferrites and Fe-Nd-B are desirable for efficient energy converters. To find interesting candidates an elaborate concept for efficient screening is required. Our bulk high-throughput approaches are well-suited to scan rapidly through multicomponent systems. Core of the approach are diffusion couples. These heterogeneous non-equilibrium states allow coverage of the most relevant part of a so far unexplored phase diagram by one single sample. By a combination of different microscopy techniques the magnetic phases are identified and analysis of the corresponding intrinsic magnetic properties is performed. From domain size and domain contrast the intrinsic material parameters can be deduced. The talk focuses on the principles of the methodology and gives examples for its successful application. The properties of the novel hard magnets (e.g. RE-lean/Ce-based, RE-free) will be presented and discussed within the framework of micromagnetism
11:30 am-12:00 am Sepehri Amin Development of high performance permanent magnets without reliance on scarce elements

Development of high coercivity Nd-Fe-B based permanent magnets without reliance on heavy-rare-earth elements have been the center of research interest of permanent magnet community in the past decade. In order to realize a high coercivity magnet, we have combined advanced multi-scale microstructure characterizations using scanning transmission electron microscopy and atom probe tomography, combined with magnetic domain observations and micromagnetic simulations to have a better understanding on microstructure-coercivity relationship [1-4]. In this talk, we will first show how a high room temperature coercivity of 2.2 T with remanent magnetization of 1.30 T is achieved in Dy-free permanent magnets by control of grain size and shape, and engineering of the grain boundary phase [5]. We will discuss how the reduction of aspect ratio in Nd2Fe14B grains and modification of the grain boundary/interface chemistry can result in improvement of thermal stability of coercivity mainly due to the reduction of local demagnetizing factor. Thereafter, we will show by infiltration of low melting point Nd-Tb-Cu alloy in the hot-deformed Nd-Fe-B magnets, ultimate permanent magnet with a coercivity of 2.5 T and remanent magnetization of 1.4 T, and excellent thermal stability of coercivity of -0.32 %/°C can be achieved. The microstructure origin for this excellent magnetic properties will be addressed based on the microstructure analysis and micromagnetic simulations. In the last part of the talk, we will show excellent intrinsic magnetic properties of Sm(Fe0.8,Co0.2)11Ti and (Sm0.8,Zr0.2)(Fe0.8,Co0.2)10.5Ti0.5 magnets making them a good candidate for the industrial applications other than Nd-Fe-B system.
[1] T.T. Sasaki et al. Acta Mater. 115, 269-277 (2016).
[2] H. Sepehri-Amin et al. Acta Mater. 99 (2015) 297.
[3] M. Soderžnik et al. Acta Mater. 135 (2017) 68-76.
[4] Xin Tang et al. Scripta Mater. 147 (2018) 108.
[5] Lihua Liu et al. AIP Advances 8 (2018) 056205.
12:00 am-12:30 pm Stuart Parker New Permanent Magnet Materials from the U.S. Critical Materials Institute: Experiment and Theory

Strong permanent magnets are an important component of energy technologies such as electric and hybrid electric vehicles. Despite this, finding permanent magnets to surpass or supplement the Nd2Fe14B magnet discovered in 1984 remains a challenge. Here I present three recent discoveries from the U.S. • The finding [1], corroborated by first principles calculations, that HfMnP possesses a very large magnetic anisotropy – approximately 8 times that of hcp Cobalt, on a per 3d atom basis.
• The theoretical result [2, 3] that La and Ce substitutions into the potential permanent magnets Sm2Fe17N3 and Sm2Fe17C3 maintain their favorable magnetic properties and improve their high-temperature stability.
• The remarkable transformation of paramagnetic CeCo3 into a potential permanent magnet [4] by Mg alloying, again substantiated by first principles calculations [5].
I close with an outlook for the future of permanent magnets.
1. T.N. Lamichhane, V. Taufour, M. W. Masters, D. S. Parker et al, Appl. Phys. Lett. 109, 092402 (2016).
2. T. Pandey, M.-H. Du, and D. S. Parker. Phys. Rev. Appl. 9, 034002 (2018).
3. T. Pandey and D.S. Parker, Sci. Rep. 8, 3601 (2018).
4. T.N. Lamichhane et al, Phys. Rev. Appl. 9, 024023 (2018)
5. T. Pandey and D.S. Parker, under review; arXiv:1802.06747 (2018).
Processing 12:30 pm-1:00 pm Ralph Skomski Tetragonal Iron-Series Transition-Metal Magnets
1:00 pm-1:30 pm DISCUSSION
1:30 pm-3:30 pm LUNCH BREAK
3:30 pm-4:00 pm Spomenka Kobe Novel Multicomponent Nd-Fe-B Permanent Magnets

The well-known rare-earth crisis motivated research focused on decreasing the use of the heavy-rare-earth (HRE) as the element, which is on the far top of the list of Critical Raw Materials. Our study presented here is only a small part of the efforts focused in the direction of minimizing the use of HRE in magnets for environmental applications.
The simulations of the effects that the demagnetizing fields have on the magnet in a motor showed that only certain parts of the magnet are exposed, and therefore only those parts need to be protected against demagnetization. The inventive idea was to develop a magnet with a significant volume fraction of its body HRE-free and just using HREs at the exposed parts to significantly improve the performance and to address the issue of the resource efficiency at the same time.
We considered two different approaches for the manufacturing of magnets with locally different magnetic properties. The first sample was prepared from the loose powders by placing one powder on top of the other, after which the powder compact was densified in a single PECS consolidation step. The second sample was manufactured from the single dense component Dy-free and Dy-containing magnets, previously prepared from the respective powders. We condensed the two parts into a single magnet body in a second PECS consolidation step. SEM and EDX analysis of the as-prepared multicomponent magnets revealed that the compositions of the respective materials remained unchanged. The results of the magnetic characterization showed that the magnetic properties of the respective materials were preserved in the multicomponent magnet. Information on the local magnetic properties was provided by cutting the multicomponent magnet in half and measuring each part individually. The magnetic properties of the two parts matched the properties of the initial powders, thus proving that a multicomponent magnet can be prepared in a short, low-temperature PECS consolidation step without degrading the properties of the basic nanostructured materials.
4:00 pm-4:30 pm Allan Walton The Hydrogen Ductilisation Process for Neodymium Iron Boron Magnets
4:30 pm-5:00 pm Frédéric Mazaleyrat Processing of Mn-Al-(C) magnets by spark plasma sintering

Among rare-earth-free permanent magnets, Mn-Al is a good candidate to fill the gap between hard ferrites and néodymium based magnets because of its potentially good functional properties and cheap constituents. However, the tetragonal hard magnetic phase is metastable and decompose into non-magnetic phases about 600°C, a temperature far below the sintering temperature using conventional sintering techniques. The spark plasma sintering technology (SPS) open new fields because of its enhence reactivity and speed. Two different processes have been investigated, starting from rapidly quenched powder. The first consist in heating the powder arround 900°C in the stable hexagonal phase for sintering, then cooling rapidly to impede the formation of equilibrium non-magnetic phases and to form the tetragonal phase. The second one, starts from metastable hexagonal phase obtained by rapid quenching, then heating is performed at a temperature between the hexagonal to tetragonal transformation (about 500°C) and the decomposition (600°C) under a high pressure (400 Mpa). The second method prove to provide material with higher purity and better hard magnetic characteristics.
5:00 pm- 7:30 pm NOVAMAG
Hour Event
NOVAMAG