Gohda Yoshihiro
Department of Materials Science and Engineering, Tokyo Institute of Technology, Yokohama, Japan.
Sci Technol Adv Mater. 2021 Feb 12;22(1):113-123. doi: 10.1080/14686996.2021.1877092.
Development of high-performance permanent magnets relies on both the main-phase compound with superior intrinsic magnetic properties and the microstructure effect for the prevention of magnetization reversal. In this article, the microstructure effect is discussed by focusing on the interface between the main phase and an intergranular phase and on the intergranular phase itself. First, surfaces of main-phase grains are considered, where a general trend in the surface termination and its origin are discussed. Next, microstructure interfaces in SmFe-based magnets are discussed, where magnetic decoupling between SmFe grains is found for the SmCu subphase. Finally, general insights into finite-temperature magnetism are discussed with emphasis on the feedback effect from magnetism-dependent phonons on magnetism, which is followed by explanations on atomic arrangements and magnetism of intergranular phases in Nd-Fe-B magnets. Both amorphous and candidate crystalline structures of Nd-Fe alloys are considered. The addition of Cu and Ga to Nd-Fe alloys is demonstrated to be effective in decreasing the Curie temperature of the intergranular phase.
高性能永磁体的发展既依赖于具有优异本征磁性能的主相化合物，也依赖于防止磁化反转的微观结构效应。在本文中，通过关注主相和晶间相之间的界面以及晶间相本身来讨论微观结构效应。首先，考虑主相晶粒的表面，讨论表面终止的一般趋势及其起源。接下来，讨论SmFe基磁体中的微观结构界面，其中发现SmCu子相对SmFe晶粒之间存在磁解耦。最后，讨论对有限温度磁性的一般见解，重点是依赖于磁性的声子对磁性的反馈效应，随后解释Nd-Fe-B磁体中晶间相的原子排列和磁性。考虑了Nd-Fe合金的非晶态和候选晶体结构。结果表明，在Nd-Fe合金中添加Cu和Ga可有效降低晶间相的居里温度。
