Role of atomic-scale thermal fluctuations in the coercivity
Role of atomic-scale thermal fluctuations in the coercivity
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DOI：
10.1038/s41524-020-0325-6
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发表时间：
2020-06
影响因子：
9.7
通讯作者：
Y. Toga;S. Miyashita;A. Sakuma;T. Miyake
中科院分区：
文献类型：
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作者：
Y. Toga;S. Miyashita;A. Sakuma;T. Miyake
有限温度下磁性能的微观机制是永磁材料研究的关键问题。在这里，我们提出了一个原子自旋模型的最高性能的磁体Nd 2Fe 14 B的磁化率的温度依赖性。对于定量分析的磁化反转与热波动，我们专注于自由能景观作为磁化的函数。自由能的计算采用复制-交换Wang-Landau方法。这种方法允许我们解决缓慢成核问题，即，热激活效应，在磁化反转。我们具体地观察到，热涨落导致了一个向下的凸性在有关温度的双折射率。此外，通过对热激活（形核）的微观过程的分析，我们发现激活体积对磁场不敏感。的不敏感性解释了线性减少的自由能垒的成核过程中的磁场。
The microscopic mechanism of coercivity at finite temperature is a crucial issue for permanent magnets. Here we present the temperature dependence of the coercivity of an atomistic spin model for the highest-performance magnet Nd2Fe14B. For quantitative analysis of the magnetization reversal with thermal fluctuations, we focus on the free energy landscape as a function of the magnetization. The free energy is calculated by the replica-exchange Wang–Landau method. This approach allows us to address a slow nucleation problem, i.e., thermal activation effects, in the magnetization reversal. We concretely observed that the thermal fluctuations lead to a downward convexity in the coercivity concerning the temperature. Additionally, through analyzing the microscopic process of the thermal activation (nucleation), we discover the activation volume is insensitive to a magnetic field around the coercivity. The insensitivity explains the linear reduction of the free energy barrier by the magnetic field in the nucleation process.