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Unmasking the interior magnetic domain structure and evolution in Nd-Fe-B sintered magnetsthrough high-field magnetic imaging of the fractured surface

Phys. Rev. Mater. 2 (2018) 104413-1-8

2018年10月26日(金)

David Billington, Kentaro Toyoki, Hiroyuki Okazaki, Yoshinori Kotani, Tomoki Fukagawa, Takeshi Nishiuchi, Satoshi Hirosawa, and Tetsuya Nakamura ( https://doi.org/10.1103/PhysRevMaterials.2.104413 )

Abstract

Conventional magnetic imaging techniques have observed magnetic domains in the polished surface of Nd-Fe-B sintered magnets, but the mechanical processing involved introduces numerous defects that facilitate the nucleation of reversed domains, thereby masking the interior domain structure. Here, we utilize high-field synchrotron x-ray magnetic circular dichroism microscopy to map the elemental and magnetic distributions in the polished and fractured surfaces of a Nd-Fe-B sintered magnet throughout its entire demagnetization process. As the applied field is varied, the domains in the fractured surface behave completely differently from those in the polished surface, thereby unmasking the interior domain structure and behavior. The area-averaged fractured surface coercivity is μ0Hfracc = 0.85 T which is much higher than the area-averaged polished surface coercivity, μ0Hpolc = 0.5 T. Most of the local magnetic hysteresis loops are positively or negatively biased from the zero of the field axis. The highest coercivity grains, some of which exceed 2 T, are almost always located in the vicinity of strongly oppositely biased adjacent grains. This indicates that these oppositely biased grains are strongly influencing the magnetostatic field at the sample surface.

その他特記事項

The x-ray absorption microscopy experiment was performed with the approval of the Japan Synchrotron Radiation Research Institute (JASRI), Proposals No. 2014B1008, No. 2015A1009, No. 2015B1016, No. 2016A1008, No. 2016B1009, and No. 2017A1022. The Elements Strategy Initiative Center for Magnetic Materials (ESICMM) is funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT). The authors would also like to thank K. Hono, S. Okamoto, and M. Takata for invaluable discussions.


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文部科学省

文部科学省
元素戦略プロジェクト(活動紹介)
NIMS磁石パートナーシップ

元素戦略拠点

触媒・電池元素戦略拠点
触媒・電池元素戦略研究拠点 (京都大学)
東工大元素戦略拠点
東工大元素戦略拠点 (東京工業大学)
構造材料元素戦略研究拠点
構造材料元素戦略研究拠点 (京都大学)
高効率モーター用磁性材料技術研究組合
高効率モーター用 磁性材料技術研究組合