Article
Materials Science, Multidisciplinary
Yuye Wu, Konstantin P. Skokov, Lukas Schafer, Fernando Maccari, Alex Aubert, Hao Xu, Haichen Wu, Chengbao Jiang, Oliver Gutfleisch
Summary: We report on the microstructure, hard magnetic properties, and thermal stability of hot-compacted nanocrystalline (Nd0.85Ce0.15)15(Fe1-xCox)7(8)B(7) permanent magnets. The substitution of Fe by Co influences the grain boundary phase composition and degrades the coercivity at lower Co concentrations (x < 0.3). At higher Co concentrations (x >= 0.6), the absence of a grain boundary phase leads to strong magnetic coupling. Additional RE(Fe,Co)2, RE(Fe,Co)4B, and RECo5 phases gradually form with increasing Co concentration (x > 0.6). A new type of microstructure with nanograins and good thermal stability is observed at x = 0.4 and 0.6. In (Nd0.85Ce0.15)(15)(Fe0.4Co0.6)78B-7 magnets, the temperature coefficient of coercivity exceeds 0.3%/K within the temperature range of 300 K-500 K and 0.23%/K for the temperature range of 300 K-650 K, demonstrating the potential for designing highly thermal-stable permanent magnets.
Article
Materials Science, Multidisciplinary
Xianshuang Xia, Xu Tang, Yeyuan Du, Haichen Wu, Jinyun Ju, Lian Wu, Renjie Chen, Wenzong Yin, Lanting Zhang, Aru Yan
Summary: High coercivities and excellent thermal stability were achieved in hot-deformed Nd-Fe-B magnets through intergranular addition of alloy powders, with a low consumption of rare-earth elements.
Article
Chemistry, Physical
Guantong Wei, Min Zhao, Xianshuang Xia, Jinyun Ju, Yeyuan Du, Yiping Huang, Xu Tang, Wenzong Yin, Renjie Chen, Aru Yan
Summary: The effects of adding (Pr0.25Nd0.75)10Dy80Cu5Al5 alloy powders on the magnetic properties and microstructure of hot-deformed Nd-Fe-B magnets were investigated. The addition of (Pr0.25Nd0.75)10Dy80Cu5Al5 resulted in an ultrahigh coercivity of 3.14 T in a 6-mm-thick hot-deformed magnet, and improved the temperature coefficient of coercivity and remanence at 20-180℃, indicating excellent thermal stability. Microstructure observations showed that the addition of (Pr0.25Nd0.75)10Dy80Cu5Al5 led to the formation of thick nonferromagnetic intergranular phase, reduced grain size and aspect ratio, and the formation of the (Nd,Pr,Dy)2Fe14B main phase, which were the main reasons for the enhancement of coercivity and thermal stability.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Chemistry, Physical
Fugang Chen, Tieqiao Zhang, Yong Zhao, Xiaoli Wang, Caiping Jiang, Jinlu Chen, Wenqiang Zhao
Summary: The demagnetization field distribution of magnetized Nd-Fe-B magnet was quantitatively calculated and analyzed. Multilayered composite Nd-Fe-B magnets were designed and fabricated with specific coercivity gradient distributions lower than the demagnetization field gradient. It was found that the low coercivity interlayer magnets did not significantly decrease the overall magnetic properties, and effective self-bonding was observed between adjacent Nd-Fe-B magnets.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Materials Science, Multidisciplinary
Yuye Wu, Konstantin P. Skokov, Lukas Schafer, Fernando Maccari, Alex Aubert, Ziyuan Rao, Kevin Schweinar, Baptiste Gault, Hao Xu, Chengbao Jiang, Oliver Gutfleisch
Summary: In this study, the similarities and differences between Nd-Fe-B and Nd-Co-B magnets were investigated. It was found that the microstructure and origin of the high coercive state in Nd-Co-B magnets, unlike Nd-Fe-B magnets, have been less studied. Nd-Co-B magnets consist of multiple exchange-coupled ferromagnetic phases.
Article
Chemistry, Physical
Xiaowei Wu, Jiaying Jin, Yongming Tao, Wang Chen, Xiaoling Peng, Mi Yan
Summary: This study prepared a series of Ce-Y-Fe-B magnets by adjusting the Ce/Y ratio, achieving a balanced contribution to coercivity and thermal stability and demonstrating excellent performance.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Chemistry, Physical
Jie Chen, Jian Liu, Minjuan Zhang, Zhanji Dong, Zhongjie Peng, Xinyi Ji, Mei Liu, Lanting Zhang, Anqi Zhang, Hong Zhu
Summary: Designing Nd-Fe-B-based permanent magnets with high temperature stability is crucial for their use in traction motors. Conventionally, heavy rare-earth elements are used for achieving high temperature stability, but at a higher cost. This study demonstrates the utilization of an adaptive learning framework to optimize the composition of Nd-Fe-B-based magnets with lower-cost elements and improve the performance-cost ratio. The framework efficiently screens novel compositions and guides the experimental design, resulting in significant improvements in the performance-cost ratio.
JOURNAL OF MATERIALS CHEMISTRY A
(2023)
Article
Materials Science, Multidisciplinary
Z. Wang, T. T. Sasaki, Y. Une, T. Ohkubo, K. Hono
Summary: Record-breaking high coercivity is achieved in Dy-free sintered magnets by separately diffusing Dy70Cu30 and Pr68Cu32 eutectic alloys. The low Dy content sample exhibits a high coercivity of 2.8 T and an excellent temperature coefficient of coercivity. The unique presence of a uniform Dy-rich shell and enriched Pr near the surface of Nd2Fe14B grains strengthens the anisotropy field, resulting in the high coercivity without alloying Dy to the initial magnet.
Article
Materials Science, Multidisciplinary
Meng Lv, Tuo Kong, Wenhuai Zhang, Mingyuan Zhu, Hongming Jin, Wenxian Li, Ying Li
Summary: Nd-Fe-B magnets are widely used in high-tech fields due to their excellent magnetic properties. With the rapid development of the electric vehicle industry, there is a higher demand for these magnets, especially in terms of coercivity. The new technology of Grain Boundary Diffusion has been proposed to effectively increase the coercivity of Nd-Fe-B magnets.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2021)
Article
Chemistry, Applied
Min Zhao, Na Liu, Xu Tang, Renjie Chen, Jinyun Ju, Wenzong Yin, Yeyuan Du, Aru Yan, Xincai Liu, Jing Pan, Zhiyi Xu
Summary: Grain boundary diffusion process (GBDP) has been applied to sintered Nd-Fe-B magnets to improve the utilization efficiency of heavy rare earth elements. Recent research shows that GBDP also has potential for enhancing the performance of hot-deformed Nd-Fe-B magnets. This review provides a comprehensive overview of the development and magnetic property enhancement mechanisms of different diffusion methods on hot-deformed magnets, and discusses the room for further property enhancement and the associated challenges of GBDP.
JOURNAL OF RARE EARTHS
(2023)
Article
Chemistry, Physical
Sumin Kim, Hyun-Sook Lee, Woo Hyun Nam, Donghwan Kim, Weon Ho Shin, Jong Wook Roh, Wooyoung Lee
Summary: The magnetic properties and thermal stability of Tb-diffused Nd-Fe-B magnets were investigated, showing that diffusion temperature plays a key role in controlling thermal stability. Magnets fabricated at high diffusion temperatures exhibited good coercivity but poor thermal stability, while those prepared at lower temperatures showed the best thermal stability. The microstructure with diffused Tb atoms was found to be mainly responsible for the enhanced thermal magnetic stability in the magnets.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Materials Science, Multidisciplinary
H. Sepehri-Amin, Xin Tang, T. Ohkubo, K. Hono
Summary: Understanding the magnetization reversal processes of permanent magnets is essential for developing magnets with high coercivity. Recent studies have used magneto-optical Kerr effect microscopy to observe the dynamic magnetic domains under an external magnetic field. Different microstructural features, such as grain boundaries and interfaces, influence the magnetization reversal processes of Nd-Fe-B-based permanent magnets. By manipulating these factors, it is possible to achieve magnets with higher coercivity.
Article
Materials Science, Multidisciplinary
Zhiheng Zhang, Hansheng Chen, Jiaying Jin, Bryan Lim, Xiaolian Liu, Wei Li, Mi Yan, Simon P. Ringer
Summary: This study presents a multi-main-phase Nd-Dy-Fe-B magnet with a Dy-lean core-Dy-rich shell microstructure, which exhibits high magnetic performance and thermal stability. The formation mechanism of the core-shell microstructure is explained through experimental and simulation analysis, highlighting the potential application of the magnet in large-scale production.
Article
Physics, Applied
Bang Zhou, Wei Li, Lin Wen, Chengyuan Xu, Xuefeng Liao, Jinbo Wei, Yu Pan, Xiaolian Liu, Song Fu, Lizhong Zhao, Hongya Yu, Xichun Zhong, Xuefeng Zhang, Zhongwu Liu
Summary: This study introduces the non-rare earth element Ge into Ce, La, and Y-based RE-Fe-B nanocrystalline alloys, successfully enhancing their magnetic properties. The (BH)(max) of 65.6 kJ/m(3) and H-cj of 346 kA/m are achieved in the [(Ce0.8La0.2)(0.5)Y-0.5](16)Fe77.5B6Ge0.5 alloy. The improvement is attributed to the increased content of the hard magnetic RE2Fe14B phase with refined grain size, which is confirmed by micromagnetic simulation. Ge addition effectively suppresses the laves phase by forming the Ce5Ge3 phase with the lowest formation energy. This work clarifies the positive role of Ge in enhancing the H-ci and (BH)(max) of nanostructured (Ce,La,Y)-Fe-B alloys.
APPLIED PHYSICS LETTERS
(2023)
Article
Engineering, Manufacturing
Olivier Tosoni, Elisa Borges Mendonca, Joni Reijonen, Atte Antikainen, Lukas Schaefer, Stefan Riegg, Oliver Gutfleisch
Summary: Additive manufacturing (AM) is a promising method for efficiently utilizing rare-earth elements in complex-shaped magnets. This study developed a close-to-industrial process to produce a narrow-distributed Nd-Fe-B powder and used it to build magnets using powder bed fusion with laser beam. After optimization and annealing, the magnets displayed excellent magnetic properties.
ADDITIVE MANUFACTURING
(2023)
Article
Physics, Applied
Pelin Tozman, Hossein Sepehri-Amin, Xin Tang, Tadakatsu Ohkubo, Kazuhiro Hono
Summary: Substitution of Co for Fe in SmFe12-based compounds realizes large saturation magnetization. This study successfully reduces the concentration of Co while maintaining a large magnetic moment in the compound. Additionally, (Sm0.8Y0.2)Fe12-based compounds exhibit superior magnetic properties compared to Nd2Fe14B.
APPLIED PHYSICS EXPRESS
(2022)
Article
Materials Science, Multidisciplinary
H. Sepehri-Amin, Xin Tang, T. Ohkubo, K. Hono
Summary: Understanding the magnetization reversal processes of permanent magnets is essential for developing magnets with high coercivity. Recent studies have used magneto-optical Kerr effect microscopy to observe the dynamic magnetic domains under an external magnetic field. Different microstructural features, such as grain boundaries and interfaces, influence the magnetization reversal processes of Nd-Fe-B-based permanent magnets. By manipulating these factors, it is possible to achieve magnets with higher coercivity.
Article
Materials Science, Multidisciplinary
Kresna B. Fathoni, Zehao Li, Tomoya Nakatani, Yuya Sakuraba, Taisuke Sasaki, Kazuhiro Hono
Summary: The MR ratio of CoFe/bcc-Cu/CoFe CIP-GMR devices grown on Si(0 0 1) substrate is slightly lower than that grown on MgO(0 0 1) substrate due to the presence of fcc phase of Cu.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Nanoscience & Nanotechnology
Kazuho Okada, Akinobu Shibata, Taisuke Sasaki, Hisashi Matsumiya, Kazuhiro Hono, Nobuhiro Tsuji
Summary: This study aimed to improve the resistance against hydrogen embrittlement by increasing the concentration of carbon segregated at prior austenite grain boundary (PAGB), XPAGB, in low-carbon martensitic steels. The specimens with and without carbon segregation treatment (Non-seg and Seg specimens, respectively) had similar microstructures, except for higher XPAGB in the Seg specimen. The Seg specimen exhibited higher maximum stress and smaller fraction of intergranular fracture surface under hydrogen-charged conditions, indicating that segregated carbon suppressed hydrogen accumulation and increased cohesive energy of PAGB.
SCRIPTA MATERIALIA
(2023)
Article
Microscopy
Sujin Lee, Atsuko Sato, Takehiro Tamaoka, Kunio Yubuta, Mitsunari Auchi, Taisuke Sasaki, Tadakatsu Ohkubo, Kazuhiro Hono, Yasukazu Murakami
Summary: This paper proposes a method using electron holography to provide a phase image of the demagnetization field (H-d) within a thin-foil permanent magnet. The observation of H-d remains challenging because electron holography can only image the magnetic flux density (B), which is a combination of contributions from magnetization (M), stray magnetic field (H-s) outside the specimen, and H-d inside the specimen. The phase map approximating H-d, determined from electron holography observation of a Nd2Fe14B single-crystalline specimen, shows good agreement with micromagnetic theory's prediction. This method can be applied to study the coercivity mechanism of permanent magnets, which is sensitive to the demagnetization field.
Article
Materials Science, Multidisciplinary
Peng Yi, Taisuke T. Sasaki, Suhas Eswarappa Prameela, Timothy P. Weihs, Michael L. Falk
Summary: Atomic-scale calculations indicate that both stress effects and chemical binding contribute to solute redistribution in the presence of vacancy clusters in magnesium alloys. The size of the vacancy cluster influences the importance of chemical binding relative to stress. These solute-vacancy interactions also affect the diffusivity of vacancies and vacancy clusters in a solid solution. Experimental observations in Mg-Al alloys support the role of solute segregation in simultaneously deformed and aged samples.
Article
Materials Science, Multidisciplinary
D. Xie, Z. H. Li, T. T. Sasaki, Y. F. Gao, Z. Y. Lyu, R. Feng, Y. Chen, K. An, H. B. Chew, T. Nakata, S. Kamado, K. Hono, P. K. Liaw
Summary: The low-alloyed Mg-Al-Ca-Mn alloy, as a new class of heat-treatable magnesium alloys, shows great engineering potential due to its excellent extrudability and high strength achieved by the dispersion of Guinier-Preston (G.P.) zones. In this study, in situ neutron diffraction measurements were conducted to investigate the cyclic deformation behavior of this alloy with and without G.P. zone dispersion. The relationship between macroscopic deformation behavior and microscopic response at the grain level, such as twinning and detwinning, was established.
Article
Materials Science, Multidisciplinary
Z. Wang, T. T. Sasaki, Y. Une, T. Ohkubo, K. Hono
Summary: Record-breaking high coercivity is achieved in Dy-free sintered magnets by separately diffusing Dy70Cu30 and Pr68Cu32 eutectic alloys. The low Dy content sample exhibits a high coercivity of 2.8 T and an excellent temperature coefficient of coercivity. The unique presence of a uniform Dy-rich shell and enriched Pr near the surface of Nd2Fe14B grains strengthens the anisotropy field, resulting in the high coercivity without alloying Dy to the initial magnet.
Article
Chemistry, Physical
Z. H. Kautsar, H. Sepehri-Amin, Xin Tang, R. Iguchi, K. Uchida, T. Ohkubo, K. Hono
Summary: The resistivities of anisotropic Nd-Fe-B-based magnets were increased in parallel and perpendicular directions to the c-axis by hot-deforming Nd-Fe-B melt-spun flakes coated with DyF3 through electrophoretic deposition. As a result, the operating temperature under high-frequency AC magnetic field decreased by 20°C due to the reduction of eddy current loss. The formation of a resistive layer composed of NdF3 at the interface of original ribbons in the hot-deformed magnet was observed. The excess Dy diffused into the original ribbon flakes and formed a Dy-rich shell in Nd2Fe14B grains, resulting in a high coercivity.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Microscopy
Jun Uzuhashi, Tadakatsu Ohkubo, Kazuhiro Hono
Summary: Atom probe tomography (APT) is a widely used technique for analyzing the microstructure of alloys and devices. In this study, a method for automatically fabricating the desired tip shape using a script-controlled FIB-SEM system was developed. The effect of intentionally changing the tip shape on APT data was also discussed.
Article
Materials Science, Multidisciplinary
Yusuke Kozuka, Taisuke T. Sasaki, Terumasa Tadano, Jun Fujioka
Summary: In this study, the fabrication and transport properties of SrPd3O4 and CaPd3O4 thin films as candidates of oxide Dirac semimetals are investigated. The observed weak temperature dependence suggests narrow-gap properties, but unintentionally doped holes hinder the discovery of the Dirac band. The study establishes the basic thermodynamics of thin-film fabrication and paves the way for exploring interesting properties of topological band structures.
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS
(2023)
Article
Nanoscience & Nanotechnology
J. J. Bhattacharyya, T. T. Sasaki, T. Nakata, S. R. Agnew
Summary: This study explains why rolled sheet material is softer and less responsive to aging compared to extruded material. By using crystal-plasticity modeling, it is shown that the initial texture of the rolled material allows for the accommodation of soft modes, such as basal slip and twinning, during in-plane tension. These modes are less affected by the finely dispersed Guinier-Preston (GP) zones, even with the same number density. In contrast, the extruded material is stronger in tension along the extrusion axis due to a higher relative activity of prismatic slip, which is strongly affected by the GP zones. This study emphasizes the significant role of initial texture in determining the strength and anisotropy of non-cubic metals and alloys.
SCRIPTA MATERIALIA
(2023)
Article
Materials Science, Multidisciplinary
Ryo Toyama, Satoshi Kokado, Keisuke Masuda, Zehao Li, Varun K. Kushwaha, Taisuke T. Sasaki, Loku Singgappulige Rosantha Kumara, Tomoyuki Koganezawa, Hiroo Tajiri, Takahiro Yamazaki, Masato Kotsugi, Yuma Iwasaki, Yuya Sakuraba
Summary: In this paper, the origin of the anisotropic magnetoresistance (AMR) effect in thin films is investigated through experimental observation and theoretical modeling. It is found that the addition of Ir atoms leads to a sign change in the AMR ratio, with the highest negative values observed at high Ir concentrations. The theoretical model confirms that this sign change is due to the B2 ordering phase. These findings provide insights into the AMR origin in heavy-metal-doped ferromagnetic alloys.
PHYSICAL REVIEW MATERIALS
(2023)
