Multiscale simulations toward understanding effects of amorphous grain boundary on coercivity in Nd-Fe-B magnets

在现代能源相关技术所必需的Nd-Fe-B磁体中，围绕Nd 2Fe 14 B晶粒的薄的非晶晶界（AG B）相被证实显著地影响磁性。但其潜在机制尚未完全了解。Nd 2Fe 14 B/AGB界面结构的多样性和纳米尺度的特点使得理解AGB对磁性的影响具有挑战性。Nd-Fe-B磁体的矫顽力不仅取决于Nd 2Fe 14 B/Ag B界面附近的电子和原子水平上的局域性质，而且还取决于原子和微观水平上的磁反转。在本计画中，我们将整合第一性原理、原子自旋模型与微磁学，进行多尺度模拟，以多层次了解Ag B对Nd-Fe-B磁铁磁性的影响。Nd 2Fe 14 B/AGB结构将通过从头算MD方案结合进化算法生成。然后从第一性原理出发，计算了Nd_2Fe_（14）B/AGB界面附近的原子分辨磁性（原子磁矩、Fe的原子MAE、Nd离子的晶场参数和原子对交换参数）。以它们为输入，原子自旋模型将被参数化和数值实现，以揭示原子尺度的磁反转。最后，结合原子自旋和微磁模拟将被应用于了解在多晶粒的情况下，AGB的双折射率的影响。原子自旋模型将被用来连接与微磁模拟计算的界面区域原子化，同时处理与微磁离散的体区域。该项目将揭示Nd_2Fe_（14）B/AGB系统中磁反转和磁势机制的多尺度图像，并激发局部磁性的原子尺度工程。

In Nd-Fe-B magnets which are essential for modern energy-related technologies, the thin amorphous grain boundary (AGB) phase surrounding Nd2Fe14B grains is confirmed to notably affect the coercivity. But the underlying mechanism is not yet fully understood. The structural diversity and nanoscale feature of Nd2Fe14B/AGB interface make understanding AGB effects on coercivity challenging. Coercivity in Nd-Fe-B magnets relies on not only the local properties at the electronic and atomic level in the Nd2Fe14B/AGB interface vicinity, but also the magnetic reversal at both the atomic and microscopic levels. In this project, we will perform multiscale simulations by integrating first principles, atomistic spin model, and micromagnetics, toward a multilevel understanding of the AGB effects on the coercivity in Nd-Fe-B magnets. The Nd2Fe14B/AGB structure will be generated by an ab initio MD scheme combined with an evolutionary algorithm. Then atomic-resolved magnetic properties (atomic magnetic moment, atomic MAE of Fe, crystal field parameters of Nd ions, and atomic-pair exchange parameters) in the vicinity of Nd2Fe14B/AGB interface with/without additional elements will be calculated from first principles. With them as input, the atomistic spin model will be parameterized and numerically implemented to reveal the atomic-scale magnetic reversal. Finally, the combined atomistic spin and micromagnetic simulations will be applied to understand the AGB effects on coercivity in the multigrain cases. Atomistic spin model will be used to link with micromagnetic simulations by calculating interfacial region atomistically while treating the bulk region with a micromagnetic discretization. This project should disclose the multiscale picture of the magnetic reversal and coercivity mechanism in Nd2Fe14B/AGB systems, and inspire an atomic-scale engineering of local magnetic properties.