Effect of the surface magnetic anisotropy of neodymium atoms on the coercivity in neodymium permanent magnets
Effect of the surface magnetic anisotropy of neodymium atoms on the coercivity in neodymium permanent magnets
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DOI：
10.1103/physrevb.103.014418
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发表时间：
2021-01
影响因子：
3.7
通讯作者：
M. Nishino;I. Uysal;S. Miyashita
中科院分区：
文献类型：
--
作者：
M. Nishino;I. Uysal;S. Miyashita
钕永磁体（${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$）是现代能量转换装置中不可或缺的材料。在有限温度下实现高矫顽力是一个重要问题。控制矫顽力的重要因素之一是磁性颗粒的表面性质。通过第一性原理研究发现，面向真空的第一层（001）表面层中的钕原子具有垂直于$c$轴的面内各向异性，这可能会降低矫顽力。着眼于表面各向异性对矫顽力的影响，我们使用反映钕磁体晶格结构的原子模型，通过随机朗道 - 利夫希茨 - 吉尔伯特方程方法研究了零温和有限温度下的矫顽力。我们研究了三种一般情况，即表面层中的钕原子对于（001）和（100）两种表面分别具有（1）无各向异性、（2）面内各向异性和（3）增强的各向异性。我们发现，与零温情况相反，由于热涨落效应，仅对第一层表面进行改性在有限温度下对矫顽力几乎没有影响。然而，对几层进行改性则会产生显著影响。我们讨论了矫顽力对温度、表面类型和改性层深度的依赖关系的细节，以及磁化反转过程中磁畴生长的特征。
The Nd permanent magnet (${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$) is an indispensable material used in modern energy conversion devices. The realization of high coercivity at finite temperatures is an important issue. One of the important ingredients for controlling the coercive force is the surface property of magnetic grains. It has been found by first-principles studies that the Nd atoms in the first (001) surface layer facing the vacuum have in-plane anisotropy perpendicular to the $c$ axis, which may decrease the coercivity. Focusing on the surface anisotropy effect on the coercivity, we examine the coercivity at zero and finite temperatures using an atomistic model reflecting the lattice structure of the Nd magnet with a stochastic Landau-Lifshitz-Gilbert equation method. We study three general cases, in which the Nd atoms in surface layers have (1) no anisotropy, (2) in-plane anisotropy, and (3) reinforced anisotropy for two types of surface, (001) and (100) surfaces. We find that in contrast to the zero-temperature case, owing to the thermal fluctuation effect, the modification of only the first surface layer has little effect on the coercivity at finite temperatures. However, the modification of a few layers results in significant effects. We discuss the details of the dependences of the coercivity on temperature, the type of surface, and modified layer depth, and also the features of domain growth in magnetization reversal.