Multiscale simulations toward calculating coercivity of Nd-Fe-B permanent magnets at high temperatures
Multiscale simulations toward calculating coercivity of Nd-Fe-B permanent magnets at high temperatures
复制标题
DOI：
10.1103/physrevmaterials.3.084406
复制
发表时间：
2019-08-09
影响因子：
3.4
通讯作者：
Xu, Bai-Xiang
中科院分区：
文献类型：
--
作者：
Gong, Qihua;Yi, Min;Xu, Bai-Xiang
提出了一种结合原子自旋模型（ASM）和微磁学模拟的计算方案，用于预测Nd-Fe-B永磁体的高温磁化率。ASM模拟计算了Nd 2Fe 14 B的饱和磁化强度、磁晶各向异性和交换刚度等随温度变化的本征参数，计算结果与实验值吻合较好.以ASM结果为输入，基于随机Landau-Lifshitz-吉尔伯特方程进行了有限温度微磁学模拟，计算了高温下的磁反转和磁化率（H-c）。发现除了各向异性场随温度的降低外，缺陷层的存在使热涨落进一步降低5-10%，使介电常数温度系数β降低0.02-0.1% K ~（-1）。计算的热激活体积随温度增加，由于具有强磁化的缺陷层（例如，1 T），但可以通过引入硬壳来降低。H-c和β都可以通过添加富含Dy的壳来增强，但是在壳厚度（t（sh））为约6-8 nm时饱和，之后进一步增加t（sh）或将Dy添加到核中不是必需的。
A computational scheme integrating the atomistic spin model (ASM) and micromagnetic simulations is proposed to predict the coercivity of Nd-Fe-B permanent magnets at high temperatures. ASM simulations are applied to calculate the temperature-dependent intrinsic parameters of Nd2Fe14B, including the saturated magnetization, magnetocrystalline anisotropy, and exchange stiffness, which are shown to agree well with the experimental values. With the ASM results as input, finite-temperature micromagnetic simulations based on the stochastic Landau-Lifshitz-Gilbert equation are performed to calculate the magnetic reversal and coercivity (H-c) at high temperatures. It is found that in addition to the decrease of anisotropy field with temperature, thermal fluctuations further reduce by 5-10% and beta (temperature coefficient of coercivity) by 0.02-0.1% K-1 in the presence of a defect layer. The computed thermal-activation volume, which increases with temperature, is shown to be enhanced by several times due to the defect layer with strong magnetization (e.g., 1 T), but can be decreased by introducing a hard shell. Both H-c and beta can be enhanced by adding the Dy-rich shell, but saturate at a shell thickness (t(sh)) around 6-8 nm after which further increasing t(sh) or adding Dy into the core is not essential.