Materials Science for High-Performance Permanent Magnets: Magnetization Process / Microstructural Stability
Sponsored by: TMS Functional Materials Division, TMS: Magnetic Materials Committee
Program Organizers: Satoshi Hirosawa, National Institute for Material Science; Matthew Kramer, Iowa State University; Oliver Gutfleisch, Technische Universitšt Darmstadt; Hae-Woong Kwon, Pukyong National University

Tuesday 2:00 PM
February 28, 2017
Room: 24C
Location: San Diego Convention Ctr

Funding support provided by: Elements Strategy Initiative Center for Magnetic Materials

Session Chair: Kazuhiro Hono, National Institute for Materials Science; Scott McCall, Lawrence Livermore National Laboratory

2:00 PM  Invited
Imaging the Changes in Magnetic Domain Structure in Nd-Fe-B Sintered Magnets throughout the Demagnetisation Process by Soft X-ray Magnetic Circular Dichroism Microscopy: David Billington1; Kentaro Toyoki1; Yoshinori Kotani1; Hiroyuki Okazaki1; Akira Yasui1; Wakana Ueno1; Satoshi Hirosawa1; Tetsuya Nakamura1; 1Japan Synchrotron Radiation Research Institute (JASRI), SPring-8
    For permanent magnetic materials, one of the most desirable properties is a large coercivity, a property that is directly related to the nucleation of reversed magnetic domains and pinning of domain walls in the bulk of the magnet. In order to understand how the coercivity depends upon the generation and evolution of reversed magnetic domains, magnetic domain observations throughout the demagnetisation process are essential. Therefore, we have developed a scanning soft x-ray magnetic circular dichroism (XMCD) microscope equipped with a superconducting magnet allowing magnetic domains observations in fractured surfaces under applied magnetic fields. In this talk, I will briefly describe our soft XMCD microscope, and demonstrate its effectiveness by showing some recent results from a commercial Nd-Fe-B sintered magnet. The authors thank T. Nishiuchi and T. Fukagawa from Hitachi Metals, Ltd. for supplying the sample. Part of this work is supported by ESICMM under the outsourcing project of MEXT.

2:20 PM  
Large-scale Micromagnetics Simulation for Initial Magnetization Process in Nd-Fe-B Hot-deformed Nanocrystalline Magnet: Hiroshi Tsukahara1; Kaoru Iwano1; Chiharu Mitsumata2; Tadashi Ishikawa1; Kanta Ono1; 1High Energy Accelerator Research Organization; 2‎National Institute for Materials Science
    For the development of high-performance permanent magnet, it is indispensable to know the magnetization dynamics. Nd-Fe-B hot-deformed nanocrystalline permanent magnets are promising materials with high coercivity without the use of heavy rare-earth elements. It is known that initial magnetization curve of Nd-Fe-B hot-deformed magnet has two-step structure, but the initial magnetization mechanism is not fully understood yet. We performed large-scale micromagnetics simulation under periodic boundary condition to investigate initial magnetization process of the Nd-Fe-B nanocrystalline permanent magnet. A simulation model contains more than 3,000 grains, and the size of this model is 2048× 2048 × 512 nm 3 with 0.3 billion calculation cells. Initial magnetization curve from our simulation clearly shows two-step behavior. In the first step, magnetic domain walls in the multi-domain grains moves and, in the second step, the magnetization of the single domain grains are reversed.

2:40 PM  
Electronic States of Rare Earth Elements in Permanent Magnet Materials Probed by X-ray Magnetic Circular Dichroism Nano-Spectroscopy: Tetsuro Ueno1; Ai Hashimoto2; Yasuo Takeichi2; Kanta Ono2; 1National Institute for Materials Science; 2High Energy Accelerator Research Organization
    Electronic state of 4f electrons of rare earth elements plays a crucial role in determining magnetic properties of rare-earth permanent magnet materials. In this study, we applied one of the most relevant X-ray technique, X-ray magnetic circular dichroism (XMCD) nano-spectroscopy using a scanning transmission X-ray microscope, to investigate 4f electronic states of various permanent magnet compounds. Highly focused X-rays enable us to probe tiny samples whose size of several micrometers square. Therefore, we can perform detailed spectroscopic analysis of single crystalline uniform samples extracted from polycrystalline bulk or powder-formed samples such as Sm2Fe17N3. Single crystalline samples were picked-up from actual magnets by microfabrication. X-ray absorption spectra and XMCD spectra were measured at the M4,5 edges of Sm for SmCo5, Sm2Fe17N3, Nd for Nd2Fe14B, NdFe11Ti, and Dy for (Nd,Dy)2Fe14B. Magnetic moments and valence states of rare earth elements will be compared among these compounds.

3:00 PM  
Fabrication of Nd-Fe-B Thin Films as a Model Material: Toshiyuki Shima1; Ryosuke Nakagawa1; Aya Sugawara1; Risa Kurosu1; Masaaki Doi1; 1Tohoku Gakuin University
    The demand of renewable and sustainable energy drives us to develop high efficient electromagnetic conversion system. In particular, the development of high performance motors consisting of rare-earth permanent magnets are strongly needed to fulfill the automotive applications such as hybrid vehicles (HVs), plug-in hybrid vehicles (PHVs) and electric vehicles (EVs). Recent studies revealed that the magnetic coupling between the main phases is thought to reduce by the grain boundary phase with Nd-rich and Cu-rich phases after post-sinter annealing. In addition, adding a small amount of Co to Nd-Fe-B sintered magnets has been done to improve the thermal stability of magnets due to increase of Currie temperature. In this talk, in order to understand the coercivity mechanism of Nd-Fe-B system, our recent studies on the effect of Co addition to the Nd-Fe-B thin films, microfabricated Nd-Fe-B dot arrays for the structure and magnetic properties have been introduced.

3:20 PM  
Data-driven Approach for Magnetic Neutron Scattering Data Analysis of Permanent Magnets Using Statistical Learning and Artificial Intelligence: Kanta Ono1; Akinori Asahara2; Hidekazu Morita2; Chiharu Mitsumata3; Masao Yano4; Tetsuya Shoji4; 1High Energy Accelerator Research Organization (KEK); 2Hitachi Ltd.; 3National Institute for Materials Science; 4Toyota Motor Corporation
    There has been a growing expectation over recent years for the application of machine learning and artificial intelligence to solve material science issues. Up to now, there is only a few application of artificial intelligence for the analysis of experimental data. Since magnetic small-angle neutron scattering (SANS) is an important technique for characterizing the bulk magnetic microstructure of permanent magnets and provides rich information on the distribution of bulk magnetization on a nanometer length scale, the analysis of the magnetic SANS data is rather complicated. We employed data-driven approach using statistical learning and Artificial Intelligence (Hitachi AI Technology/H) for the analysis of magnetic SANS data and got important aspects of magnetization reversal process of Nd-Fe-B hot-deformed magnets.

3:40 PM Break

4:00 PM  Invited
Phase Equilibria in the Nd-based Permanent Magnets: Taichi Abe1; Ikuo Ohnuma1; Yoshinao Kobayashi2; Ying Chen3; Osamu Takeda3; 1NIMS; 2Tokyo Institute of Technology; 3Tohoku University
    Microstructural design/control is a key technology for development of the Nd-based permanent magnets, where thermodynamic calculations based on the CALPHAD methodology can have an important role. For Nd-Fe-B-based multi-component systems, we have been constructing a thermodynamic database to estimate phase equilibria between the Nd2Fe14B compound and various phases at grain boundaries. The present version of the database is still preliminary; the applicable composition ranges are limited to up several at.% of additives. We have intensively improved it to include oxygen and other key elements through the intensive collaborations.

4:25 PM  
Stability Origin of Binary Systems Relevant to Multi-component Phase in Nd-Fe-B: Ying Chen1; Arkapol Saengdeejing1; 1Tohoku University
    In the Nd-Fe-B permanent magnet materials, several elements such as C, B, Cu, Dy, etc. are added to the main phase in order to improve the properties of the magnets from various aspects. The formation, mixing properties within various binary systems relevant to the multi-component phase have important effect on the microstructure formation so as to the coercivity of the magnets. First-principles calculations combined with the cluster expansion method (CEM) have been performed on series of binary systems such as Nd-O, Fe-Nd, Nd-Dy, Fe-Dy, Cu-Nd, Cu-Fe to investigate the ground state stability of ordered phases as well as solid solutions, in order to reveal the characteristic features of electronic structures and atomic interactions of the systems with intrinsic stability and intrinsic instability. Such information is significant in understanding the properties of the multi-component phase, also provides the basic data for further study of the thermodynamic properties.

4:45 PM  
Ab-initio Study of Transition-metal-doping Effects on the Magnetic Anisotropy in Nd-Fe- B Sintered Magnets: Yasutomi Tatetsu1; Shinji Tsuneyuki2; Yoshihiro Gohda3; 1The University of Tokyo; 2The University of Tokyo, ISSP; 3The University of Tokyo, Tokyo Institute of Technology
    As reported in several experimental studies for Nd-Fe-B magnets, doping the small amount of transition elements, for example Ni, Cu, Zn, and Ga, into Nd-Fe-B magnets increases the coercivity. We calculated formation energies of transition-metal (TM) -doped Nd2Fe14B bulk and surface systems and the magnetic anisotropy K1 of Nd from first principles in order to understand which elements can improve the magnetic anisotropy K1 of Nd. Here, TM = Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge. We used the computational code OpenMX. From the analysis of the formation energies in these systems, we find that the Fe 4c site at the surface is easily replaced by TM atoms. Especially in the surface systems, doping Ni, Cu, Zn, and Ga at the Fe 4c site improves K1 of Nd and the formation energies of these systems are lower than that of other systems.

5:05 PM  Invited
Grain Boundary Diffusion of Co, Cu and Nb as Function of Temperature in NdFeB: Gino Hrkac1; Thomas Schrefl2; Johann Fischbacher2; Thomas Ostler1; Richard Evans3; Sam Westmoreland3; Michael Winklhofer4; Roy Chantrell3; Gergely Zimanyi5; 1University of Exeter; 2Danube University Krems; 3University of York; 4University of Duisburg; 5University of California Davis
    We perform molecular-dynamics simulations to understand the impact of Co,Cu and Nb diffusion on the NdFeB-phase at different temperatures 300-600K. It is shown that for large Co-concentrations a disruptive behavior of Co in the NdFeB-matrix can be observed. This distortions are found to lead to periodic displacement, indicating that a strain is acting on the whole crystal and produces a profiling effect. Temperature studies show doping materials such as Co, Nb, and Cu diffuse easier into a Fe-rich boundary phase than into a Nd-rich. By doing that the doping materials produce sharp distortion profiles, 5-10Angstrom. Quantitative analysis shows that smaller infiltration-profiles produce sharp transition phases, e.g. Cu, hence improving anisotropy profile. Further we show that all dopants and especially Cu tends to accumulate at the interface between two phases as function of temperature. In conclusion, Cu and Co can be used to reduce strain effects at the interface.