Green Magnetic Materials Group

Featured Works

Graphical abstract for efficient magnetic cooling through covalent bond control.

Advanced Materials (2026)

Control of covalent bond enables efficient magnetic cooling

A new cryogenic regenerator material made only from abundant elements like copper, iron, and aluminum has been developed, eliminating the need for rare‑earth metals or liquid helium. By exploiting magnetic “frustration” effects, the material can cool to around 4 K, offering promise for more stable and sustainable cooling in technologies such as MRI systems and quantum computers

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Physical Metallurgy

Book Chapter | Physical Metallurgy, 6 eds. (2026)

Physical Metallurgy of Permanent Magnets

Permanent magnets are crucial to modern technologies, and this chapter reviews both established and emerging magnet materials while explaining how intrinsic properties and microstructural control determine magnetic performance. It highlights advanced fabrication, characterization, and computational approaches - such as micromagnetics and digital twins - that enable the design of sustainable, high‑performance next‑generation magnets

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Graphical abstract for cryogenic cooling material based on abundant elements

Scientific Reports (2025)

Innovative cryogenic cooling material using spin frustration from abundant elements

In collaboration with the National Institute of Technology (KOSEN), Oshima College, NIMS succeeded in developing a new regenerator material composed solely of abundant elements, such as copper, iron, and aluminum, that can achieve cryogenic temperatures (approx. 4 K = −269°C or below) without using any rare-earth metals or liquid helium. By utilizing a special property called "frustration" found in some magnetic materials, where the spins cannot simultaneously satisfy each other's orientations in a triangular lattice, the team demonstrated a novel method that replaces the conventional rare-earth-dependent cryogenic cooling technology. The developed material holds promise for responding to the lack of liquid helium as well as for application to stable cooling in medical magnetic resonance imaging (MRI) and quantum computers, which is expected to see further growth in demand.

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Graphical abstract for low-loss Fe-enriched soft magnetic ribbons.

Nature Communications (2025)

Ultra-low core loss in Fe-enriched soft magnetic ribbons enabled by nanostructure and high-frequency domain engineering

This work combines nanostructure optimization and domain engineering to significantly reduce magnetic core loss in iron-based ribbons, supporting energy-efficient high-frequency magnetic devices

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Graphical abstract for tomography-based digital twin of Nd-Fe-B magnets.

npj Computational Materials (2024)

Tomography-based digital twin of Nd-Fe-B permanent magnets

A digital-twin workflow built from 3D FIB-SEM tomography reconstructs real microstructures of permanent magnets, enabling predictive simulations that connect defects and grain morphology to magnetic performance

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Graphical abstract for creation of flexible spin-caloritronic material with giant transverse thermoelectric conversion by nanostructure engineering

Nature Communications (2024)

Creation of flexible spin-caloritronic material with giant transverse thermoelectric conversion by nanostructure engineering

This work shows that a short heat treatment can rapidly convert widely used soft magnetic materials into high-performance thermoelectric conversion media, enabling scalable and practical device fabrication

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Publications

2026

  1. Long-period incommensurate magnetic orderings associated with the large magnetocaloric effect in GdCo2B2

    S.R. Larsen, N. Terada, H. Mamiya, H. Saito, T. Nakajima, S. Itoh, P. Manuel, D. Khalyavin, F. Orlandi, and H. Kitazawa

    Physical Review B 113(10) (2026) 104411

    DOI: 10.1103/yyx5-3dnv

  2. Near-surface defects break symmetry in water adsorption on CeO2-x(111)

    O. Custance, M. Gonzalez Lastre, K. Kim, Estefania Fernandez-Villanueva, P. Pou, M. Abe, H. Sepehri-Amin, S. Kawai, M. Veronica Ganduglia-Pirovano, and R. Perez

    Communications Materials 7 (2026) 39

    DOI: 10.1038/s43246-025-01011-x

  3. High-throughput development of flexible amorphous materials showing large anomalous Nernst effect via automatic annealing and thermoelectric imaging

    S.J. Park, R. Gautam, A. Alasli, T. Hirai, F. Ando, H. Nagano, H. Sepehri-Amin, and K.-I. Uchida

    Materials Today 92 (2026) 416

    DOI: 10.1016/j.mattod.2025.12.027

  4. Effect of Cr substitution for Mn on magnetic and transverse thermoelectric properties of isotropic Mn1-xCrxAlGe magnets

    A. Martin-Cid, B. Madavali, F. Ando, N. Kulesh, K.-I. Uchida, and H. Sepehri-Amin

    Journal of Alloys and Compounds 1057 (2026) 186802

    DOI: 10.1016/j.jallcom.2026.186802

  5. Control of covalent bond enables efficient magnetic cooling

    Xin Tang, Y. Miura, N. Terada, E. Xiao, S. Kobayashi, A. Doring, T. Tadano, A. Martin-Cid, T. Ohkochi, S. Kawaguchi, Y. Matsushita, T. Ohkubo, T. Nakamura, K. Skokov, O. Gutfleisch, K. Hono, and H. Sepehri-Amin

    Advanced Materials 38(7) (2026) e14295

    DOI: 10.1002/adma.202514295

2025

  1. Zero-field hybridization of anomalous Nernst and off-diagonal Seebeck effects in artificially tilted multilayers

    Y. Lee, F. Ando, T. Hirai, R. Modak, H. Sepehri-Amin, and K.-I. Uchida

    Annalen der Physik 537(8) (2025) e00127

    DOI: 10.1002/andp.202500127

  2. Ultra-low core loss in Fe-enriched soft magnetic ribbons enabled by nanostructure and high-frequency domain engineering

    R. Gautam, S. Hiramoto, N. Kulesh, H. Mamiya, S. Okamoto, N. Ono, T. Ogasawara, T. Ohkubo, and H. Sepehri-Amin

    Nature Communications 16 (2025) 8022

    DOI: 10.1038/s41467-025-63139-1

  3. Tailoring the microstructure and formation of hexagonal-BN segregants in FePt-based granular films for improved HAMR media

    D. Ogawa, H. Sepehri-Amin, and Y. K. Takahashi

    Journal of Alloys and Compounds 1032 (2025) 180243

    DOI: 10.1016/j.jallcom.2025.180243

  4. Systematic investigation on transverse thermoelectric conversion of RE2(Fe,Co)14B (RE = rare-earth) compounds

    B. Madavali, F. Ando, T. Hirai, A. Martin-Cid, K.-I. Uchida, and H. Sepehri-Amin

    Science and Technology of Advanced Materials 26(1) (2025) 2520162

    DOI: 10.1080/14686996.2025.2520162

  5. Simultaneous achievement of large anomalous Nernst effect and reduced thermal conductivity in sintered polycrystalline topological Heusler ferromagnets

    K. Oyanagi, H. Sepehri-Amin, K. Takamori, T. Tadano, T. Imamura, R. Nagasawa, K. Mahalingam, T. Hirai, F. Ando, Y. Sakuraba, S. Kobayashi, and K.-I. Uchida

    Acta Materialia 296 (2025) 121239

    DOI: 10.1016/j.actamat.2025.121239

  6. Role of neutron Bragg-edge spectroscopy in development of practical magnetic materials

    H. Mamiya, N. Terada, K. Hiroi, T. Shinohara, and H. Sepehri-Amin

    Journal of Applied Physics 138 (2025) 143904

    DOI: 10.1063/5.0285904

  7. Reduced hysteresis in La0.7Ce0.3Fe11.5Si1.5 hydrides by grain size reduction

    M.M. Prusty, S.H. Molleti, H. Takanobu, S.R.K. Malladi, Xin Tang, and H. Sepehri-Amin

    Science and Technology of Advanced Materials 26 (2025) 2525742

    DOI: 10.1080/14686996.2025.2525742

  8. Numerical simulation of active magnetic regenerative refrigeration using Gyroid structured regenerator at room temperature

    S. Nishioka, H. Sepehri-Amin, and A.T. Saito

    International Journal of Refrigeration 170 (2025) 468

    DOI: 10.1016/j.ijrefrig.2024.11.018

  9. Nonvolatile magneto-thermal switching driven by vortex trapping in commercial In-Sn solder

    P. Rani, T. Murakami, Y. Watanabe, H. Sepehri-Amin, H. Arima, A. Yamashita, and Y. Mizuguchi

    Applied Physics Express 18 (2025) 033001

    DOI: 10.35848/1882-0786/adb6ee

  10. Multifunctional composite magnet realizing record-high transverse thermoelectric generation

    F. Ando, T. Hirai, A. Alasli, H. Sepehri-Amin, Y. Iwasaki, H. Nagano, and K.-I. Uchida

    Energy and Environmental Science 18(9) (2025) 4068

    DOI: 10.1039/d4ee04845h

  11. Mechanism of continuous intergranular phase formation in Sm(Fe,Ti,V)12-based sintered magnets by post-sinter annealing

    J.S. Zhang, Xin Tang, T. Ohkubo, K. Hono, and H. Sepehri-Amin

    Acta Materialia 294 (2025) 121160

    DOI: 10.1016/j.actamat.2025.121160

  12. Magnetic correlations and crystal structure changes in Fe- and Ni-substituted ErCo2 with reversible giant magnetocaloric effect

    S.R. Larsen, N. Terada, Xin Tang, H. Mamiya, Y. Nambu, D. Okuyama, and H. Sepehri-Amin

    Physical Review B 112 (2025) 014443

    DOI: 10.1103/6lt2-4pwb

  13. Lattice expansion due to hydrogen absorption into β-rhombohedral boron

    T. Hiroto, H. Sepehri-Amin, N. Uemura, N. Miyauchi, W. Hayami, T. Ohkubo, T. Ogitsu, K. Soga, and K. Kimura

    Solid State Sciences 163 (2025) 107907

    DOI: 10.1016/j.solidstatesciences.2025.107907

  14. High-temperature deformation and consolidation of polycrystalline α-SiC by spark plasma sintering

    D. Demirskyi, H. Sepehri-Amin, and O.O. Vasylkiv

    International Journal of Applied Ceramic Technology 22(2) (2025) e14967

    DOI: 10.1111/ijac.14967

  15. Heavy rare earth-free high resistivity and coercivity Nd-Fe-B hot-deformed magnet developed by Pr-Cu diffusion and CaF2-LiF eutectic addition

    Z.H. Kautsar, H. Sepehri-Amin, Xin Tang, N. Kulesh, T.T. Sasaki, T. Ohkubo, and K. Hono

    Journal of Alloys and Compounds 1010 (2025) 177738

    DOI: 10.1016/j.jallcom.2024.177738

  16. Foreword to the focus issue: materials science and technology for magnetic thermal management

    K.-I. Uchida, Y. Sakuraba, and H. Sepehri-Amin

    Science and Technology of Advanced Materials 26 (2025) 2604891

    DOI: 10.1080/14686996.2025.2604891

  17. Evaluation of Ho100-x-yErxCey magnetic refrigerants using advanced multisample neutron transmission spectroscopy

    H. Mamiya, N. Terada, S.R. Larsen, N. Tsujii, K. Hiroi, T. Shinohara, and H. Sepehri-Amin

    Physical Review Research 7 (2025) 013233

    DOI: 10.1103/PhysRevResearch.7.013233

  18. Enhanced mechanical performance of HoB2-based compounds without sacrificing cryogenic magnetocaloric effects

    Z. Wang, A.M. Doring, O. Vasylkiv, Xin Tang, K.P. Skokov, N. Terada, T. Ohkubo, O. Gutfleisch, and H. Sepehri-Amin

    Acta Materialia 296 (2025) 121227

    DOI: 10.1016/j.actamat.2025.121227

  19. Effect of Co on twin formation and magnetic properties of Sm(Fe,Ti,V)12 alloys

    P. Tozman, G. Hrkac, C.E. Patrick, J.B. Staunton, T. Saito, T. Sasaki, T. Ohkubo, and H. Sepehri-Amin

    Scripta Materialia 258 (2025) 116491

    DOI: 10.1016/j.scriptamat.2024.116491

  20. Designing flexible magnetic materials for zero-magnetic-field operation of the anomalous Nernst effect

    S.J. Park, R. Modak, R. Gautam, A. Alasli, T. Hirai, F. Ando, H. Nagano, H. Sepehri-Amin, and K.-I. Uchida

    Acta Materialia 301 (2025) 121422

    DOI: 10.1016/j.actamat.2025.121422

  21. Data-driven compositional optimization of La(Fe,Si)13-based magnetocaloric compounds for cryogenic applications

    A.K. Srinithi, A. Bolyachkin, Xin Tang, H. Sepehri-Amin, S. Dieb, A.T. Saito, T. Ohkubo, and K. Hono

    Scripta Materialia 258 (2025) 116486

    DOI: 10.1016/j.scriptamat.2024.116486

  22. Combinatorial sputtering synthesis of TbCu7-type Sm-Fe based compounds: A study on phase, composition, and extrinsic magnetic properties

    A.R. Dilipan, H. Sepehri-Amin, R. Modak, V.K. Kushwaha, Y. Sakuraba, K. Uchida, K. Hono, and Y.K. Takahashi

    Journal of Alloys and Compounds 1010 (2025) 177723

    DOI: 10.1016/j.jallcom.2024.177723

  23. Automated identification of the origin of energy loss in nonoriented electrical steel by feature extended Ginzburg-Landau free energy framework

    M. Taniwaki, R. Nagaoka, K. Masuzawa, S. Sato, A.L. Foggiatto, C. Mitsumata, T. Yamazaki, I. Obayashi, Y. Hiraoka, Y. Igarashi, Y. Mizutori, S.A. Hossein, T. Ohkubo, H. Mogi, and M. Kotsugi

    Scientific Reports 15 (2025) 23758

    DOI: 10.1038/s41598-025-00357-z

  24. Achieving high-density L10-FePt granular films on an electrically conductive (Mg,Ti)O underlayer for HAMR media

    A.R Dilipan, H. Sepehri-Amin, I. Suzuki, and Y.K Takahashi

    Scripta Materialia 268 (2025) 116885

    DOI: 10.1016/j.scriptamat.2025.116885

2024

  1. Guidelines for communicating commensurate magnetic structures. A report of the International Union of Crystallography Commission on Magnetic Structures

    J. M. Perez-Mato, B. J. Campbell, V. O. Garlea, F. Damay, G. Aurelio, M. Avdeev, M. T. Fernandez-Diaz, M. S. Henriques, D. Khalyavin, S. Lee, V. Pomjakushin, N. Terada, O. Zaharko, J. Campo, O. Fabelo, D. B. Litvin, V. Petricek, S. Rayaprol, J. Rodriguez-Carvajal, and R. Von Dreele

    Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials 80(4) (2024) 219-234

    DOI: 10.1107/S2052520624004268

  2. Investigation of High-Pressure Phase of the Frustrated Antiferromagnet CuFeO2 by Using Polarized and Unpolarized Neutron Diffraction Experiments with Hybrid-Anvil-Cell

    N. Terada

    The Review of High Pressure Science and Technology 34(3) (2024) 114-120

    DOI: 10.4131/jshpreview.34.114

  3. Elastic and inelastic neutron scattering experiments under high pressure in the frustrated antiferromagnet CuFeO2

    N. Terada, D.D. Khalyavin, P. Manuel, S. Asai, T. Masuda, H. Saito, T. Nakajima, and T. Osakabe

    Physical Review B 110(2) (2024) 024406

    DOI: 10.1103/PhysRevB.110.024406

  4. Stroboscopic time-of-flight neutron diffraction in long pulsed magnetic fields

    T. Nakajima, M. Watanabe, Y. Inamura, K. Matsui, T. Kanda, T. Nomoto, K. Ohishi, Y.Kawamura, H. Saito, H. Tamatsukuri, N. Terada, and Y. Kohama

    Physical Review Research 6(2) (2024) 023109

    DOI: 10.1103/PhysRevResearch.6.023109

  5. Tomography-based digital twin of Nd-Fe-B permanent magnets

    A. Bolyachkin, E. Dengina, N. Kulesh, Xin Tang, H. Sepehri-Amin, T. Ohkubo, and K. Hono

    npj Computational Materials 10 (2024) 34

    DOI: 10.1038/s41524-024-01218-5

  6. Observation of nonvolatile magneto-thermal switching in superconductors

    H. Arima, Md. R. Kasem, H. Sepehri-Amin, F. Ando, K.-I. Uchida, Y. Kinoshita, M. Tokunaga, and Y. Mizuguchi

    Communications Materials 5 (2024) 34

    DOI: 10.1038/s43246-024-00465-9

  7. Microstructure and coercivity of Al-diffused Sm(Fe,Co,B)12 film

    H. Sepehri-Amin, N. Kulesh, Y. Mori, T. Ohkubo, K. Hono, and T. Shima

    Scripta Materialia 242 (2024) 115955

    DOI: 10.1016/j.scriptamat.2023.115955

  8. Micromagnetic simulations of Nd-Fe-B hot-deformed magnets subjected to eutectic grain boundary diffusion process

    A. Bolyachkin, E. Dengina, H. Sepehri-Amin, T. Ohkubo, and K. Hono

    Scripta Materialia 247 (2024) 116095

    DOI: 10.1016/j.scriptamat.2024.116095

  9. Magnetic and magneto-transport properties of non-collinear antiferromagnetic Mn3Ge epitaxial films

    Y. Takeuchi, H. Sepehri-Amin, S. Sugimoto, T. Hiroto, and S. Kasai

    APL Materials 12 (2024) 071110

    DOI: 10.1063/5.0217710

  10. Insights into reduction of hysteresis in (Mn,Fe)2(P,Si) compounds by experimental approach and Landau theory

    Z. Wang, E. Dengina, A. Kosogor, T. Hiroto, Xin Tang, N. Kulesh, A. Bolyachkin, T. Ohkubo, and H. Sepehri-Amin

    Materialia 37 (2024) 102195

    DOI: 10.1016/j.mtla.2024.102195

  11. Hybridizing anomalous Nernst effect in artificially tilted multilayer based on magnetic topological material

    T. Hirai, F. Ando, H. Sepehri-Amin, and K.-I. Uchida

    Nature Communications 15 (2024) 9643

    DOI: 10.1038/s41467-024-53723-2

  12. Hybrid transverse magneto-thermoelectric cooling in artificially tilted multilayers

    K.-I. Uchida, T. Hirai, F. Ando, and H. Sepehri-Amin

    Advanced Energy Materials 14(3) (2024) 2302375

    DOI: 10.1002/aenm.202302375

  13. Exchange-coupled Fe-Pt / Ru / Fe-Pt nanogranular films as potential heat-assisted-magnetic-recording media with reduced writing temperature

    D. Ogawa, A. Bolyachkin, A.R. Dilipan, N. Kulesh, H. Sepehri-Amin, and Y.K. Takahashi

    Physical Review Applied 22 (2024) 054060

    DOI: 10.1103/PhysRevApplied.22.054060

  14. Excellent intrinsic magnetic properties in the TbCu7-type Sm-Fe-N compound

    A.R. Dilipan, D. Ogawa, H. Sepehri-Amin, P. Tozman, T. Hiroto, K. Hono, and Y.K. Takahashi

    Acta Materialia 274 (2024) 119996

    DOI: 10.1016/j.actamat.2024.119996

  15. Dual-layer FePt-C granular media for multi-level heat-assisted magnetic recording

    P. Tozman, S. Isogami, I. Suzuki, A. Bolyachkin, H. Sepehri-Amin, S.J. Greaves, H. Suto, Y. Sasaki, T.Y Chang, Y. Kubota, P. Steiner, P.W. Huang, K. Hono, and Y.K. Takahashi

    Acta Materialia 271 (2024) 119869

    DOI: 10.1016/j.actamat.2024.119869

  16. Creation of flexible spin-caloritronic material with giant transverse thermoelectric conversion by nanostructure engineering

    R. Gautam, T. Hirai, A. Alasli, H. Nagano, T. Ohkubo, K.-I. Uchida, and H. Sepehri-Amin

    Nature Communications 15 (2024) 2184

    DOI: 10.1038/s41467-024-46475-6

  17. Coercivity limits in Nd-Fe-B hot-deformed magnets with ultrafine microstructure

    N. Kulesh, A. Bolyachkin, E. Dengina, Xin Tang, T. Ohkubo, T. Kajiwara, H. Miyawaki, H. Sepehri-Amin, and K. Hono

    Acta Materialia 276 (2024) 120159

    DOI: 10.1016/j.actamat.2024.120159

  18. (Nd,Sm,La)-Fe-B-based hot-deformed magnets with excellent comprehensive properties for variable flux permanent magnet motors

    A.K. Srinithi, Xin Tang, H. Sepehri-Amin, T. Ohkubo, and K. Hono

    Acta Materialia 281 (2024) 120387

    DOI: 10.1016/j.actamat.2024.120387

2023

  1. Crystal electric field level scheme leading to giant magnetocaloric effect for hydrogen liquefaction

    N. Terada, H. Mamiya, H. Saito, T. Nakajima, T.D. Yamamoto, K. Terashima, H. Takeya, O. Sakai, S. Itoh, Y. Takano, M. Hase, and H. Kitazawa

    Communications Materials 4(1) (2023) 13

    DOI: 10.1038/s43246-023-00340-z

  2. Unveiling the origin of the large coercivity in (Nd,Dy)-Fe-B sintered magnets

    Xin Tang, J. Li, H. Sepehri-Amin, A. Bolyachkin, A. Martin-Cid, S. Kobayashi, Y. Kotani, M. Suzuki, A. Terasawa, Y. Gohda, T. Ohkubo, T. Nakamura, and K. Hono

    NPG Asia Materials 15 (2023) 50

    DOI: 10.1038/s41427-023-00498-5

  3. Microstructure evolution in FePt-Cr2O3 granular thin films

    I. Suzuki, T. Abe, H. Sepehri-Amin, K. Hono, and Y.K. Takahashi

    Journal of Magnetism and Magnetic Materials 579 (2023) 170874

    DOI: 10.1016/j.jmmm.2023.170874

  4. High-coercivity SmFe12-based anisotropic sintered magnets by Cu addition

    A.K. Srinithi, Xin Tang, H. Sepehri-Amin, J. Zhang, T. Ohkubo, and K. Hono

    Acta Materialia 256 (2023) 119111

    DOI: 10.1016/j.actamat.2023.119111

  5. Exploring secondary phases in the Sm-Fe-V system beneficial for coercivity

    P. Tozman, H. Sepehri-Amin, T. Abe, K. Hono, and Y.K. Takahashi

    Acta Materialia 258 (2023) 119197

    DOI: 10.1016/j.actamat.2023.119197

  6. Data-driven optimization of FePt heat-assisted magnetic recording media accelerated by deep learning TEM image segmentation

    N. Kulesh, A. Bolyachkin, I. Suzuki, Y.K. Takahashi, H. Sepehri-Amin, and K. Hono

    Acta Materialia 255 (2023) 119039

    DOI: 10.1016/j.actamat.2023.119039

  7. Control of grain density by varying lattice mismatch in FePt-C film for heat assisted magnetic recording

    I. Suzuki, H. Sepehri-Amin, K. Hono, and Y.K. Takahashi

    Journal of Alloys and Compounds 968 (2023) 172196

    DOI: 10.1016/j.jallcom.2023.172196