Article
Chemistry, Physical
Sangen Luo, Munan Yang, Zaiping Xu, Tongyun Zhao, Sajjad Ur Rehman, Xi Yu, Shuwei Zhong, Haitao Wang, Chaoxiang Jin, Qiang Ma, Bin Yang
Summary: This paper investigates the effect of grain size in the diffusion matrix on the grain boundary diffusion mechanism of Tb element. The results show that with only 0.75 wt. % TbF3 diffusion, the intrinsic coercivity increases significantly for the magnet with finer average grain size compared to the coarse-grain magnet. The increase in intrinsic coercivity is attributed to the increase in defect density and the higher grain orientation caused by grain refinement, which leads to improved diffusion efficiency and magnetic properties.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
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
Yaping Wu, Minggang Zhu, Peng Shen, Yikun Fang, Qisong Sun, Lele Zhang, Chao Wang, Xiaolong Song, Meng Zheng, Wei Li
Summary: The corrosion resistance of sintered Nd-Fe-B magnets can be improved by adding Ni and Cr. The addition of Ni and Cr in the novel sintered Nd-Ni-Fe-Cr-B magnet enhances the corrosion resistance of both the grain boundary phase and the main phase. The reduced potential difference between the two phases further enhances the corrosion resistance of the magnet.
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T
(2023)
Article
Chemistry, Physical
Amit Mishra, Sina Khoshsima, Tomaz Tomse, Benjamin Podmiljsak, Saso Sturm, Carlo Burkhardt, Kristina Zuzek
Summary: The recycling of rare earth-based permanent magnets is crucial for the future supply of rare earth elements. This study developed a method to extract (Nd, Pr)2Fe14B from sintered Nd-Fe-B magnets through chemical leaching of secondary, rare earth-rich phases. The use of mild organic acid as a leaching medium makes the process environmentally friendly.
Article
Chemistry, Physical
Hao Zhan, Yinan Wang, Chuanxiao Peng, Juntao Yu, Zilong Wang, Jiakai Hu, Xinyuan Bai, Yang Luo, Li Wang
Summary: To improve the diffusion characteristics of heavy rare earth in the grain boundary, the effects of diffusion process and the ratio of Tb and Cu during the layered deposition process on the magnetic properties of Tb-Cu diffused Nd-Fe-B magnets were systematically investigated. The coercivity of the diffused magnet was most enhanced with RTb/Cu = 4:1, increasing from 10.86 kOe to 21.80 kOe. Cu significantly improved the composition homogenization of diffused magnets. The highest utilization efficiency of Tb reached 43.96 kOe/wt% in the designed diffused magnet. Moreover, the reduced demagnetization risk of sintered Nd-Fe-B magnets was verified using finite element method based on the experimental temperature characteristics of the magnet. (c) 2023 Elsevier B.V. All rights reserved.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Chemistry, Physical
Ruipeng Qian, Hechang Han, Fugang Chen, Hui Sun, Yong Zhao, Peilei Zhang, Wenqiang Zhao
Summary: Grain boundary diffusion process was performed on sintered Nd-Ce-Fe-B magnets with different Ce concentrations. The coercivity increment and remanence improvement were observed in the magnets with higher Ce concentrations. The (Pr, Tb)-rich shells were formed, contributing to the enhancement of coercivity and remanence.
Article
Nanoscience & Nanotechnology
Y. M. Tao, J. Y. Jin, L. Z. Zhao, X. L. Liu, Z. H. Zhang, G. H. Bai, C. Wu, J. M. Greneche, K. Lv, B. Xin, M. Yan
Summary: Grain boundary (GB) engineering is used to control the composition and magnetism of the 1:2 phase in Nd-Ce-Fe-B nanostructured magnets. A Cu-mediated GB engineering strategy is proposed, which enables the formation of a continuous 1:2 GB phase and the generation of a novel Nd-dominated 1:2 phase with a ferro-paramagnetic transformation. At the optimal Cu doping, the magnet exhibits the highest coercivity and coexistence of paramagnetic and ferromagnetic 1:2 phases.
MATERIALS TODAY NANO
(2022)
Article
Materials Science, Multidisciplinary
M. B. Siva Kumar, D. Prabhu, M. Sadhasivam, B. Manjusha, N. Chandrasekaran, K. G. Pradeep, G. Sundararajan, R. Gopalan
Summary: We investigated the effect of grain boundary diffusion of Nd-Cu eutectic phase and the influence of Nb on the microstructure and magnetic properties of Nd-Fe-B melt-spun ribbons. Our findings show that Nb clusters promote the decoration of Nd-Cu grain boundaries while limiting grain growth during diffusion annealing. The coercivity of the samples was significantly enhanced after diffusion annealing, making them suitable for high-temperature applications.
MATERIALS RESEARCH LETTERS
(2022)
Article
Materials Science, Multidisciplinary
Hao Zhan, Chuanxiao Peng, Yuzhao Xue, Xianrui Wang, Xiao Lin, Xinyuan Bai, Li Wang
Summary: By investigating the impact of deposition sequences on the magnetic properties of sintered Nd-Fe-B magnets, it was found that the deposition of an appropriate amount of Cu can increase the diffusion depth of Tb, while excessive Cu deposition reduces the diffusion efficiency of Tb.
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T
(2023)
Article
Chemistry, Physical
Yuheng Xie, Shuai Cao, Xuejing Cao, Tengfei Wu, Mingpeng Kou, Zhi Jia, Guangfei Ding, Shuai Guo, Renjie Chen, Xincai Liu, Aru Yan, Zhiyi Xu
Summary: This study systematically investigated the magnetic properties and microstructures of sintered Nd-Fe-B magnets with different Nd-Cu powder additions and their corresponding diffused magnets using Tb-Cu alloys. The results showed that the enhancement of coercivity after diffusion was positively correlated with the intergranular phase proportion of the base substrates. Furthermore, the analysis of microstructures revealed that the higher coercivities were mainly attributed to the deeper diffusion depths of Tb elements and the presence of Nd-rich grain boundary phases in the base substrates, which facilitated the diffusion process.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Materials Science, Multidisciplinary
Y. L. Huang, Y. F. Yao, F. Y. Wang, H. F. Li, Z. J. Wu, Q. Feng, W. Li, J. M. Luo, Z. S. Pang, C. C. Zhong, Y. H. Hou
Summary: In this paper, the diffusion of non-heavy rare earth PrNdAl alloy was investigated to enhance the coercivity of magnetic materials. The results showed that the diffusion of PrNdAl alloy significantly improved the coercivity, with three factors contributing to this improvement: the enhancement of magnetic hardening, the weakening of intergranular exchange coupling, and the enhancement of magnetic isolation effect.
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T
(2022)
Article
Chemistry, Applied
Shuwei Zhong, Munan Yang, Sajjad Ur Rehman, Sangen Luo, Longgui Li, Chao Li, Jiajie Li, Shuhua Xiong, Ihor Bulyk, Bin Yang
Summary: In order to solve the uneven distribution issue of the core-shell structure in sintered Nd-Fe-B magnets, this study suggests using high-melting-point and reactive element titanium (Ti) as an additive to enhance the diffusion of heavy rare earth elements along the grain boundary phase. The addition of Ti significantly increases the diffusion depth and intrinsic coercivity of the magnets. The formation of TiB2 phase improves the crystal structure arrangement and enhances the activity of the grain boundary phase, leading to improved diffusion and distribution in the magnets.
JOURNAL OF RARE EARTHS
(2023)
Article
Chemistry, Physical
Fugang Chen, Hechang Han, Tieqiao Zhang, Yong Zhao, Xiaoli Wang, Wenqiang Zhao
Summary: Grain boundary diffusion process (GBDP) can improve the coercivity and remanence of sintered Nd-Ce-Fe-B magnets. Ce substitution promotes the diffusion process, but excessive Ce content leads to the formation of abnormally large grains on the magnet surface.
JOURNAL OF ALLOYS AND COMPOUNDS
(2022)
Review
Materials Science, Multidisciplinary
Zhongwu Liu, Jiayi He, Qing Zhou, Youlin Huang, Qingzheng Jiang
Summary: The magnetic performance of Nd-Fe-B magnets is dependent on the grain boundary structure. Intergranular addition and grain boundary diffusion (GBD) processes using non-rare earth sources have been effective in enhancing coercivity. This review summarizes the development and use of non-RE diffusion sources for coercivity enhancement, discussing the properties-microstructure relationships and future directions for non-RE GBD.
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY
(2022)
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
A. Bolyachkin, H. Sepehri-Amin, I. Suzuki, H. Tajiri, Y. K. Takahashi, K. Srinivasan, H. Ho, H. Yuan, T. Seki, A. Ajan, K. Hono
Summary: This study investigates the effects of structural defects on the magnetic properties of FePt-X nanogranular media using transmission electron microscopy (TEM) images and micromagnetic simulations. A new method for evaluating structural defects is developed and validated. The study directly links the nanostructure to the magnetic properties, enabling optimization of heat-assisted magnetic recording (HAMR) media and design of magnetic nanomaterials in general.
Article
Materials Science, Multidisciplinary
Jiawei Lai, A. Bolyachkin, N. Terada, S. Dieb, Xin Tang, T. Ohkubo, H. Sepehri-Amin, K. Hono
Summary: Fe2P-type compounds exhibit a giant magnetocaloric effect and are studied for room temperature applications. In this study, rare-earth-free compounds with cryogenic magnetocaloric effect were optimized using data mining and machine learning, demonstrating promising magnetocaloric performance.
Article
Materials Science, Multidisciplinary
P. Tozman, T. Fukazawa, D. Ogawa, H. Sepehri-Amin, A. Bolyachkin, T. Miyake, S. Hirosawa, K. Hono, Y. K. Takahashi
Summary: The effect of V on the phase stability and intrinsic magnetic properties of SmFe12-xVx (0 <= x <= 1.9) thin films and bulk samples is investigated. V can stabilize the ThMn12-type phase and decrease lattice parameters. Above a certain limit, the formation of a Sm-rich phase is observed. Moreover, the introduction of V can enhance the Curie temperature and anisotropy field while decreasing the magnetization. V-substituted compounds exhibit higher anisotropy field than other compounds in a certain temperature range.
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
Physics, Applied
S. Kusaka, T. T. Sasaki, K. Sumida, S. Ichinokura, S. Ideta, K. Tanaka, K. Hono, T. Hirahara
Summary: Superlattice films composed of Bi-2 bilayers and Bi2Te3 quintuple layers were fabricated by annealing pure Bi2Te3 films. Two distinct stoichiometric phases were formed, Bi1Te1 (QL-BL-QL) and Bi4Te3 (QL-BL), and the surface-state dispersion was measured to analyze the topological nature of each sample.
APPLIED PHYSICS LETTERS
(2022)
Article
Materials Science, Multidisciplinary
J. S. Zhang, Xin Tang, A. Bolyachkin, A. K. Srinithi, T. Ohkubo, H. Sepehri-Amin, K. Hono
Summary: This study investigates the microstructure transformation and extrinsic performance change in anisotropic Sm(Fe,Ti,V)(12)-based sintered magnets by reducing the Ti content and partially substituting Fe with Co. It is found that reducing the Ti content eliminates a secondary Fe2(Ti,V) phase, resulting in improved remanence and energy density, while maintaining a relatively high coercivity. However, substituting Co for Fe leads to decreased remanence and coercivity.
Article
Chemistry, Multidisciplinary
Yudai Yamaguchi, Yuya Kanitani, Yoshihiro Kudo, Jun Uzuhashi, Tadakatsu Ohkubo, Kazuhiro Hono, Shigetaka Tomiya
Summary: In this study, the compositional and structural investigations of threading dislocations (TDs) in InGaN/GaN multiple quantum wells were conducted using correlative transmission electron microscopy (TEM) and atom probe tomography (APT). The results showed that indium atoms diffuse along the TD and their concentration decreases with distance from the InGaN layer. It was directly observed that the indium atoms originating from the InGaN layer diffuse toward the epitaxial GaN surface through the TD, possibly via the pipe diffusion mechanism induced by strain energy relaxation.
Article
Nanoscience & Nanotechnology
E. Dengina, A. Bolyachkin, H. Sepehri-Amin, K. Hono
Summary: This paper presents a machine learning method to evaluate the demagnetization curves of FePt granular films. The predicted parameters of magnetic anisotropy and defect volume fractions were in good agreement with experimental results. This study provides a new approach for characterizing and optimizing the structure of FePt granular media.
SCRIPTA MATERIALIA
(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
Nanoscience & Nanotechnology
T. Nakata, Z. H. Li, T. T. Sasaki, K. Hono, S. Kamado
Summary: This study reports the influence of grain boundary segregation on microstructure development during hot-rolling of AZ31 alloy. Annealing at 420 degrees C induces strong grain boundary segregation, promoting dynamic recrystallization and strong basal texture. Annealing at 500 degrees C reduces grain boundary segregation, hindering dynamic recrystallization and resulting in a weak rolling-direction-split texture, improving the stretch formability of the alloy sheet.
SCRIPTA MATERIALIA
(2022)
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
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
Engineering, Electrical & Electronic
Ruma Mandal, Yuta Sasaki, Ivan Kurniawan, Jiwon Jung, Yoshio Miura, Yuya Sakuraba, Kazuhiro Hono, Yukiko K. Takahashi
Summary: In this work, a high-temperature time-resolved magneto-optical Kerr effect microscopy is developed to measure the magnetization dynamics at elevated temperatures, providing a crucial understanding of the damping mechanism for highly anisotropic ferromagnetic materials and its dependence on temperature.
ACS APPLIED ELECTRONIC MATERIALS
(2022)
