Multiscale Examination of Strain Effects in Nd-Fe-B Permanent Magnets
Multiscale Examination of Strain Effects in Nd-Fe-B Permanent Magnets
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DOI：
10.1103/physrevapplied.8.014011
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发表时间：
2016-11
影响因子：
4.6
通讯作者：
M. Yi;Hongbin Zhang;O. Gutfleisch;Bai-Xiang Xu
中科院分区：
文献类型：
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作者：
M. Yi;Hongbin Zhang;O. Gutfleisch;Bai-Xiang Xu
我们用第一性原理和微磁学相结合的方法研究了Nd-Fe-B磁体的应变效应。对Nd2Fe14B的第一性原理计算表明，磁晶各向异性(K)对沿c轴的形变不敏感，而ab面内收缩是K降低的原因。与以前的唯象模型相比，预测的K对晶格形变更为敏感。双轴和三轴应力状态对K的影响较大，在ab双轴应力状态下，在较宽的应变范围内出现负K。用第一性原理对NdFeB磁体进行的微磁模拟结果表明，在晶界和三重结附近2 nm宽的区域内，3-4%的局域应变导致了负的局域K，从而使矫顽力降低了约60%。局域ab双轴应力状态更有可能导致较大的矫顽力损失。除了局部应力状态和应变水平本身，界面和晶间相的形状也对决定矫顽力有影响。对NdFeB磁体的三重区边缘进行平滑处理，减小尖角，有利于提高磁体的矫顽力。
We have performed a combined first-principles and micromagnetic study on the strain effects in Nd-Fe-B magnets. First-principles calculations on Nd2Fe14B reveal that the magnetocrystalline anisotropy (K) is insensitive to the deformation along c axis and the ab in-plane shrinkage is responsible for the K reduction. The predicted K is more sensitive to the lattice deformation than what the previous phenomenological model suggests. The biaxial and triaxial stress states have a greater impact on K. Negative K occurs in a much wider strain range in the ab biaxial stress state. Micromagnetic simulations of Nd-Fe-B magnets using first-principles results show that a 3-4% local strain in a 2-nm-wide region near the interface around the grain boundaries and triple junctions leads to a negative local K and thus decreases the coercivity by ~60%. The local ab biaxial stress state is more likely to induce a large loss of coercivity. In addition to the local stress states and strain levels themselves, the shape of the interfaces and the intergranular phases also makes a difference in determining the coercivity. Smoothing the edge and reducing the sharp angle of the triple regions in Nd-Fe-B magnets would be favorable for a coercivity enhancement.