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論文

2025

Designing nanoparticles: The role of process parameters in thermal plasma synthesis
K. Park, Y. Hirayama, and M. Shigeta
Advanced Powder Technology, 36 (2025) 104793

2024

Mechanism of reduction-diffusion reaction in Sm–Fe binary system at low temperature using molten salts
J. Kim, S. Okada, K. Takagi, and K. Ozaki
Journal of Rare Earth, 42 (10) (2024) 1889-1894

TbCu7-type Sm-Fe(-N) powder synthesized by low-temperature reduction-diffusion process using the Li–Ca reductant
J. Kim, S. Okada, J. Wang, and K. Takagi
Heliyon, 10(10) (2024) e31463

Upgrading recycling of Al–7 wt% Si alloys using electromagnetic force in directional solidification
T. Tamura, M.J. Li
Journal of Alloys and Compounds, 979 (2024) 173528.

High performance Permanent Magnet Materials Prepared by Induction Thermal Plasma Process（Review Article）
Yusuke HIRAYAMA, Masaya SHIGETA
Journal of Smart Processing - for Materials, Environment & Energy 13(1) (2024) 23-30.

D03-ordered Fe3Al magnetic nanopowders synthesized by low oxygen induction thermal plasma
J. Wang, Y. Hirayama, Z. Liu, S. Tsurumi, M. Shigeta, M. Sugimoto, J. Yoshikawa, S. Kumon, K. Sato
Journal of Alloys and Compounds 976 (2024) 173277

Effects of quenching on the microstructure and magnetic properties of MnBi nanopowders synthesized by low-oxygen induction thermal plasma
J. Wang, Y. Hirayama, M.Z. Bian, and K. Takagi
Scripta Materialia, 240 (2024) 115830

2023

Preparation of Sm–Fe–N Hard Magnetic Nanopowder From Micrometer-Sized Sm–H and Fe Mixed Powder
Y. Hirayama, Z. Liu, W. Yamaguchi, K. Takagi, K. Ozaki
IEEE Transactions on Magnetics 59(11) (2023) 1-4.

Investigation on crystallographic alignment of Sm-Co alloy nanoparticles by external magnetic field
K. Park and Y. Hirayama
Advanced Powder Technology, 34 (2023) 104238

Nanotwin-assisted nitridation of quenched FeNi alloy nanopowders for rare-earth-free magnets
J. Wang, Y. Hirayama, K. Suzuki, K. Park, Z. Liu, K. Takagi, and K, Ozaki
Journal of Materials Science & Technology, 165, (2023) 244-252

Fabrication of Al-CNT composite with high hardness and electrical conductivity by controlling Al4C3 formation
D. Kim, Y. Hirayama, Z. Liu, K. Takagi and M. Kobashi
Journal of Alloys and Compounds, 942 (2023) 169102

Cold consolidation and coercivity enhancement in Sm2Fe17N3 magnets by high-pressure torsion
A. Hosokawa and Y. Hirayama
Scripta Materialia, 226 (2023) 115251

Low-temperature synthesis of Sm-Fe binary compounds by reduction-diffusion process using an eutectic salt solvent
J Kim, S Okada, K Takagi
Rare Metals, (2023) 1-8, Published online

Low temperature synthesis of Sm-Fe alloy powder by reduction-diffusion process using new reductant of Li-Ca eutectic melt
J Kim, S Okada, K Takagi
AIP Advances 13(2) (2023) 025124

2022

Recent Research Trend in Powder Process Technology for High-Performance Rare-Earth Permanent Magnets
K. Takagi, Y. Hirayama, S. Okada, A. Hosokawa and W. Yamaguchi
KONA Powder and Particle Journal, (2022) 2023007

Ultra-high coercivity Sm-Co bulk magnets with remarkable thermal stability
K. Park, Y. Hirayama, J. Wang and M. Kobashi
Scripta Materialia, 218 (2022) 114847

Massive transformation in FeNi nanopowders with nanotwin-assisted nitridation
J. Wang, Y. Hirayama, Z. Liu, K. Suzuki, W. Yamaguchi, K. Park, K. Takagi, H. Kura, E. Watanabe and K. Ozaki
Scientific Reports 12 (2022) 3679

TbCu7-type Sm-X-Fe compounds (X = Zr, Hf, Y, Dy, La, Ce and Nd) synthesized by low-temperature reduction-diffusion (LTRD) process using molten salt
J Kim, S Okada, K Takagi
AIP Advances 12(3) (2022) 035306

Exchange-Coupled SmCo₅/Fe Nanocomposite Magnet Prepared by Low Oxygen Powder Metallurgy Process
K. Park, Y. Hirayama, W. Yamaguchi, M. Kobashi and K. Takagi
IEEE Transactions on Magnetics 58 (2022) 1-5

Surface Cleaning Effect of Bare Aluminum Micro-Sized Powder by Low Oxygen Induction Thermal Plasma
D. Kim, Y. Hirayama, K. Takagi and H. Kwon
Materials 15 (2022) 1553

Spatial composition distribution of a Ni-Cu binary alloy powder in a thermal plasma process
Y. Hirayama, M. Shigeta, K. Takagi and K. Ozaki
Journal of Alloys and Compounds 898 (2022) 162792

2021

新規ThMn12 系希土類磁石の現状と展望
小川大介，平山悠介，高橋有紀子，嶋敏之
まぐね 16 (2021) 51

Computational study of quenching effects on growth processes and size distributions of silicon nanoparticles at a thermal plasma tail
M. Shigeta, Y. Hirayama, E. Ghedini
Nanomaterials 11(6) (2021) 1370

Anisotropic Sm-Co nanopowder prepared by induction thermal plasma
K. Park, Y. Hirayama, M. Shigeta, Z. Liu, M. Kobashi, K. Takagi
Journal of Alloys and Compounds 882(15) (2021) 160633

Mechanism of anomalous α-Fe formation from stoichiometric Sm₂Fe₁₇ jet-milled powder during post-pulverization annealing
A. Hosokawa, K. Suzuki, W. Yamaguchi, K. Takagi
Acta Materialia 213 (2021) 116981

Novel powder processing technologies forproduction of rare-earth permanent magnets
K. Takagi, Y. Hirayama, S. Okada, W. Yamaguchi, K. Ozaki
Science and Technology of Advanced Materials 22 (2021) 150-159

Anisotropic Nd-Fe ultrafine particles with stable and metastable phases prepared by induction thermal plasma
Y. Hirayama, M. Shigeta, Z. Liu, N. Yodoshi, A. Hosokawa, K. Takagi
Journal of Alloys and Compounds, 873 (2021) 159724

Exchange-coupled SmCo5/Fe nanocomposite magnet prepared by low oxygen powder metallurgy process
K. Park, Y. Hirayama, W. Yamaguchi, M Kobashi, K. Takagi
IEEE Transactions on Magnetics, 58 (2021) 1-5.

Highly Conductive Al/Al Interfaces in Ultrafine Grained Al Compact Prepared by Low Oxygen Powder Metallurgy Technique
D. Kim, Y. Hirayama, M. Kobashi, Z. Liu, H. Kong, K. Takagi
Nanomaterials 11 (2021) 1182

Production of anisotropic Sm-Fe-N magnet sheets by modified powder rolling
A. Hosokawa, N. Yoneyama, I. Nakanowatari, H. Eguchi, K. Takagi
Materials Letters, 294 (2021) 129815

Influences of microstructure on macroscopic crystallinity and magnetic properties of Sm-Fe-N fine powder produced by jet-milling
Hosokawa, W. Yamaguchi, K. Suzuki, K. Takagi
Journal of Alloys and Compounds, 869 (2021) 159288

2020

Effects of nonmagnetic overlay metals on coercivity of Sm₂Fe₁₇N₃ magnet powders
W. Yamaguchi and K. Takagi
Journal of Magnetism and Magnetic Materials 516 (2020)167327

Possibility of high-performance Sm₂Fe₁₇N₃ sintered magnets by low-oxygen powder metallurgy process
K. Takagi, R. Soda, M. Jinno, W. Yamaguchi
Journal of Magnetism and Magnetic Materials, 506 (2020)166811

Metal-coated Sm₂Fe₁₇N₃ magnet powders with an oxide-free direct metal-metal interface
W. Yamaguchi, R. Soda, K. Takagi
Journal of Magnetism and Magnetic Materials, 498 (2020) 166101

2019

Semisolid state sintering behavior of aluminum–stainless steel 316L composite materials by powder metallurgy
Kwangjae Park, Dasom Kim, Kyungju Kim, Seungchan Cho, Kenta Takagi and Hansang Kwon
Materials, 12(2019) 1473

Stoichiometric study of metastable TbCu₇type Sm-Fe phase synthesized by HDDR treatment
K. Takagi, M. Jinno
Materials, 12(2019) 1473

Synthesis of Sm₂Fe₁₇N₃ powder having a new level of high coercivity by preventing decrease of coercivity in washing step of reduction-diffusion process
S. Okada, E. Node, K. Takagi, Y. Fujikawa, Y. Enokido, C. Moriyoshi, Y. Kuroiwa
Journal of Alloys and Compounds, 804 (2019) 237-242

Anisotropic nanocomposite Nd-Fe-B magnets produced by hot deformation with assistance of Nd-Cu
A. Hosokawa, K. Takagi
Journal of Magnetism and Magnetic Materials, 489 (2019) 165453

Experimental investigation of nitrogenation process for heavy rare earth nitrides from their hydrides
Y. Hirayama, K. Suzuki, A. Fujita, K. Takagi
AIP Advances, 9 (2019) 045221

Evaluation of compositional homogeneity of Fe-Co alloy nanoparticles prepared by thermal plasma synthesis
Y. Hirayama, K. Takagi
Journal of Alloys and Compounds, 792 (2019) 594-598

High-contrast imaging of magnetic domains by magneto-optical Kerr effect using plasmon filters
T. Hasegawa, M. Mizojiri, K. Takagi, K. Ozaki
Proc. Photonic and Phononic Properties of Engineered Nanostructures, San Francisco, March 2019, pp. 1092721

Role of surface iron oxides in coercivity deterioration of Sm₂Fe₁₇N₃ magnet associated with low temperature sintering
W. Yamaguchi, R. Soda, K. Takagi
Materials Transactions, 60 (2019) 479-483

Severe plastic deformation of Nd-Fe-B nanocomposite magnets at room temperature
A. Hosokawa, K. Takagi, T. Kuriiwa, Y. Inoue, K. Ozaki
Journal of Magnetism and Magnetic Materials, 473 (2019) 51-60

2018

Consolidation of Sm₂Fe₁₇N₃ magnets with Sm-based eutectic alloy binder
K. Otogawa, K. Takagi, T. Asahi
Journal of Alloys and Compounds, 746 (2018) 19-26

Powder consolidation of Nd-Fe-B/α-Fe nanocomposite materials by cold deformation process
A. Hosokawa, K. Takagi
AIP Advances, 8 (2018) 095019

Coercivity recovery effect of Sm-Fe-Cu-Al alloy on Sm₂Fe₁₇N₃ magnets
K. Otogawa, T. Asahi, M. Jinno, W. Yamaguchi, K. Takagi, H. Kwon
Journal of the Korean Physical Society, 72 (2018) 716-725

Cold welding behavior of fine bare aluminum powders prepared by new low oxygen induction thermal plasma system
Y. Hirayama, K. Suzuki, W. Yamaguchi, K. Takagi
Journal of Alloys and Compounds, 768 (2018) 608-612

Multi-scale electron microscopy of overnitrided Sm-Fe-Mn-N powder
A. Hosokawa, K. Takagi
AIP Advances, 8 (2018) 055031

Simulation-aided development of magnetic-aligned compaction with pulsed magnetic field
R. Soda, K. Tanaka, K. Takagi, K. Ozaki
Powder Technology, 329 (2018) 364-370

Preparation of TbCu₇-type Sm-Fe powders by low-temperature HDDR treatment
K. Takagi, M. Jinno, K. Ozaki
Journal of Magnetism and Magnetic Materials, 454 (2018) 170-175

2017

The formation mechanism of the nanocrystalline cells in Sm₂Fe₁₇N_x powder during overnitridation
A. Hosokawa, K. Takagi
Acta Materialia, 136 (2017), 366-377

Thermal stability of Sm₂Fe₁₇N₃ magnet powder
N. Imaoka, K. Takagi, K. Ozaki, T. Iriyama, H. Kato
Journal of Physics: Conf. Series, 903 (2017) 012042

Nanocomposite Nd-Fe-Ti-B magnets produced by melt spinning and flash annealing
A. Hosokawa, K. Takagi, T. Kuriiwa
Journal of Magnetism and Magnetic Materials, 439 (2017) 220-227

Preparation of submicron-sized Sm₂Fe₁₇N₃ fine powder with high coercivity by reduction-diffusion process
S. Okada, K. Suzuki, E. Node, K. Takagi, K. Ozaki, Y. Enokido
Journal of Alloys and Compounds, 695 (2017) 1617-1623

Improvement of magnetization of submicron-sized high coercivity Sm₂Fe₁₇N₃ powder by using hydrothermally synthesized sintering-tolerant cubic hematite
S. Okada, K. Suzuki, E. Node, K. Takagi, K. Ozaki, Y. Enokido
AIP Advances, 7 (2017) 056219

Preparation of highly dispersed core- shell α″-Fe₁₆N₂/SiO₂ particles using hydroxyapatite as a sintering prevention layer
K. Suzuki, A. Towata, Y. Kinemuchi, D. Nagai, M. Yasuoka
Journal of The Ceramic Society of Japan, 125 (2017) 565-568

2016

Synthesis of submicron-sized acicular goethite and platelet-like hematite particles and dependence of magnetic properties of α-Fe particles on their shape and size
S. Okada, K. Takagi, K. Ozaki
Materials Chemistry and Physics, 171 (2016) 171-177

Direct preparation of submicron-sized Sm₂Fe₁₇ ultra-fine powders by reduction-diffusion technique
S. Okada, K. Takagi, K. Ozaki
Journal of Alloys and Compounds, 663 (2016) 872-879

Numerical simulation of magnetic -aligned compaction with pulsed magnetic field
R. Soda, K. Takagi, K. Ozaki
Scripta Materialia, 120 (2016) 41-44

Anisotropic Sm₂Fe₁₇N₃ sintered magnets without coercivity deterioration
R. Soda, K. Takagi, M. Jinno, W. Yamaguchi, K. Ozaki
AIP Advances, 6 (2016) 115108

Exchange coupling between soft magnetic ferrite and hard ferromagnetic Sm₂Fe₁₇N₃ in ferrite/ Sm₂Fe₁₇N₃ composites
N. Imaoka, E. Kakimoto, K. Takagi, K. Ozaki, M. Tada, T. Nakagawa, M. Abe
AIP Advances, 6 (2016) 056022

Investigation of optimal route to fabricate submicron-sized Sm₂Fe₁₇ particles with reduction-diffusion method
S. Okada, K. Takagi, K. Ozaki
AIP Advances, 6 (2016) 056018

Study of entropic characteristics of strongly correlated systems using VO₂ as a model case
A. Fujita, Y. Kinemuchi, W. Yamaguchi
Physical Chemistry Chemical Physics, 18 (2016) 30824-30829

2015

Synthesis of submicron plate-like hematite without organic additives and reduction to plate-like α-Fe
S. Okada, K. Takagi, K. Ozaki
Materials Letters, 140 (2015) 135-139

Preparation of Nd-Fe-B sintered magnets from HDDR-processed powder
K. Takagi, M. Akada, R. Soda, K. Ozaki
Journal of Magnetism and Magnetic Materials, 461 (2015) 461-466

Extended particle-based simulation for magnetic-alignedcompaction of hard magnetic particles
R.Soda, K. Takagi, K. Ozaki
Journal of Magnetism and Magnetic Materials, 396 (2015) 128-134

2014

Discrete Element Simulation for Magnetic-Aligned Compaction of Magnetic Powders
R. Soda, K. Takagi, K. Ozaki
Proc. TMS2014, pp. 347-352

High-pressure sintering behavior of α”-Fe₁₆N₂ nanopowder
K. Takagi, M. Akada, K. Ozaki, N. Kobayashi, T. Ogawa, M. Takahashi
Journal of Applied Physics, 115 (2014) 103905

熱分解性磁性粉末の高密度焼結と焼結体の結晶粒子界面の研究
高木健太，中山博行，尾崎公洋
粉体および粉体粉末冶金, 61 (2014) 165-170

Size-dependent catalytic activity of platinum nanoparticles for aqueous-phase reforming of glycerol
W. Yamaguchi, Y. Tai
Chemistry Letters, 43 (2014) 313-315

著書・刊行物 / Authors and Publications

高木健太

次世代永久磁石の開発最前線：第2章2節異方性Sm₂Fe₁₇N₃焼結磁石の開発 pp.177-183（尾崎公洋，杉本諭編）
NTS出版 2019年2月

岡田　周祐

次世代永久磁石の開発最前線：第2章3節 Sm₂Fe₁₇N₃高保磁力磁石粉末の開発 pp.185-192（尾崎公洋，杉本諭編）
NTS出版 2019年2月

平山悠介

次世代永久磁石の開発最前線：第4章2節 ThMn₁₂構造の高性能磁石としての可能性pp.235-240（尾崎公洋，杉本諭編）
NTS出版 2019年2月

細川明秀、高木健太

過窒化したSm-Fe-N磁石粗粉のナノセル構造のマルチスケール観察
まてりあ 58 (2019) 77

高木健太

磁性材料・部品の最新開発事例と応用技術：サマリウム－鉄－窒素系粉末の焼結磁石製造技術
技術情報協会 2018年3月

新聞記事 / Articles

平山悠介

「永久磁石」: 産総研マガジンほか 2024年12月2日

細川明秀，山口渡，平山悠介ほか

「サマリウム-鉄-窒素（Sm₂Fe₁₇N₃）永久磁石の高密度化技術を開発
　ー高耐熱を実現するポストネオジム磁石として、EV用などの高効率モーターへの展開に期待ー」: 日本経済新聞ほか 2024年9月11日 pp. 7

細川明秀

「塑性加工法を利用したSm₂Fe₁₇N₃の成形手法の可能性」: 鉄鋼新聞 2023年12月11日 pp. 5

平山悠介

「耐熱性永久磁石の開発」: 日刊産業新聞ほか 2023年5月11日 pp. 25

高木健太

「技術で未来拓く」: 日刊工業新聞 2018年9月20日 pp. 25.

岡田　周祐

「拓く研究人」: 日刊工業新聞 2017年8月23日，pp. 27.

尾崎公洋，高木健太，曽田力央

「サマリウム鉄窒素磁石」: 日刊工業新聞2015年9月21日

受賞 /Awards

2024/11/17

Jian Wang，Yusuke Hirayama，Kenta Takagi，Masayuki Murata: The Japan Society of Vacuum and Surface Science(JVSS); Excellent Presentation Award「Atomic-scale characterization of D03-ordered Fe₃Si magnetic nanopowders for magneto-thermoelectric application」

2020/9/1

Shusuke Okada: The Institute of Electrical Engineers of Japan 技術・材料・共通部門表彰　「還元拡散法による高保持力Sm₂Fe₁₇N₃微粉末の合成」
Kwangjae Park: The Institute of Electrical Engineers of Japan IEEJ Excellent Presentation Award "Preparation of SmCo alloy fine powder by induction thermal plasma"

2019/3/6

Yusuke Hirayama: 永井科学技術財団研究奨励賞「ThMn₁₂構造を有する最強磁石化合物の作製」
Kenta Takagi: 永井科学技術財団学術賞「Sm-Fe-N異方性焼結磁石の実現に関する研究」

2018/9/19

Yusuke Hirayama: 2018年度まてりあ賞「ThMn₁₂構造を持つ高特性永久磁石材料の可能性と課題」

2016/8/31

S. Okada, K. Suzuki, E. Node, K. Takagi, K. Ozaki, Y. Enokido: REPM2016, Poster Award “Preparation of submicron-sized Sm₂Fe₁₇N₃ powder with high coercivity”