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Most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets

SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 2021, VOL. 22, NO. 1, 386–403

2021年6月4日(金)

Jiangnan Li , Hossein Sepehri-Amin , Taisuke Sasaki , Tadakatsu Ohkubo and Kazuhiro Hono

Abstract

Physically, the coercivity of permanent magnets should scale with the anisotropy field of ferromagnetic compounds, HA; however, the typical coercivity values of commercial polycrystalline sintered magnets are only ~0.2 HA, which is known as Brown’s paradox. Recent advances in multi-scale microstructure characterizations using focused ion beam scanning electron microscope (FIB/SEM), aberration corrected scanning transmission electron microscopy (Cs-corrected STEM), and atom probe tomography (APT) revealed detailed microstructural features of commercial and experimental Nd-Fe-B magnets. These investigations suggest the magnetism of a thin layer formed along grain boundaries (intergranular phase) is a critical factor that influences the coercivity of polycrystalline magnets. To determine the magnetism of the thin intergranular phase, soft X-ray magnetic circular dichroism and electron holography play critical roles. Large-scale micromagnetic simulations using the models that are close to real microstructure incorporating the recent microstructure characterization results gave insights on how the coercivity and its thermal stability is influenced by the microstructures. Based on these new findings, coercivity of Nd-Fe-B magnets is being improved to its limit. This review replies to the most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets based on our recent studies.




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文部科学省
元素戦略プロジェクト(活動紹介)
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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