Magnetization reversal analysis of permanent magnet considering local demagnetizing field

2019 Fiscal Year Final Research Report

• Project/Area Number: 17H03376
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Physical properties of metals/Metal-base materials
• Research Institution: Tohoku University
• Principal Investigator: Kitakami Osamu 東北大学, 多元物質科学研究所, 教授 (70250834)
• Co-Investigator(Kenkyū-buntansha): 岡本 聡 東北大学, 多元物質科学研究所, 准教授 (10292278) ; 菊池 伸明 東北大学, 多元物質科学研究所, 助教 (80436170)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 永久磁石 / 磁化反転 / 保磁力 / 磁壁 / 粒界

Outline of Final Research Achievements

NdFeB magnets play crucial roles in modern technologies, such as electric vehicles and power generators. At high operation temperatures, however, the performance severely deteriorates due to the coercivity decay. The aim of the present study is to clarify how one can enhance the coercivity by revealing the magnetization process.
We have carefully traced elementary magnetization processes occurring in single nanostructured NdFeB magnets consisting of a few magnetic domains by means of the highly sensitive magnetization detection technique and the x-ray circular dichroism. It has been found that the magnetization proceeds by domain wall displacement and the coercivity is dominated by the pinning of the domain walls at crystal grain boundaries. According to the micromagnetics simulation as well as the experiment mentioned above, the coercivity is found to be effectively enhanced by weakening the exchange stiffness of the boundary phase.

Free Research Field

磁性材料

Academic Significance and Societal Importance of the Research Achievements

低環境負荷の先端技術を支える材料としてNdFeB磁石は重要な役割を果たしている．それらのエネルギー利用効率向上には，一層の保磁力増強が切望されている．本研究では，各種先端技術を組み合わせることにより，NdFeB磁石内で起きる磁化反転の素過程を詳細に調べ，その保磁力が結晶粒界の磁壁ピニング力に支配されることを初めて明らかにした．保磁力に及ぼす粒界制御の影響については長年議論されてきたが，本研究はその重要性を初めて実証したものである．この成果に基づけば，粒界を非磁性化に向かわせる元素添加もしくは組織制御プロセスの最適化により，さらなる高保磁力化を実現できる可能性がある．