标题： 铁镍合金中的晶格空位迁移势垒，以及为什么镍原子扩散缓慢：第一性原理研究 显示英文标题

标题： Lattice vacancy migration barriers in Fe-Ni alloys, and why Ni atoms diffuse slowly: An ab initio study

摘要： 在铁磁性$\textrm{Fe}_x \textrm{Ni}_{1-x}$合金 ($0.4 \leq x \leq 0.6$) 中，Fe 和 Ni 原子的迁移率通过第一性原理电子结构计算框架进行研究，使用非弹性带 (NEB) 方法准确量化晶格空位迁移的能量势垒。 原子无序的 ($A1$) 面心立方相，以及原子有序的四方形$\textrm{L}1_0$相——该相被认为是一种用于先进工程应用的无稀土“间隙”磁体材料——均被研究。 在一系列针对超胞构型的 NEB 计算中，这些构型涵盖了多种成分并包含无序、部分有序和完全有序结构，我们发现 Ni 原子始终显著地比 Fe 原子不那么活泼。 关键的是，我们能够根据铁磁合金的自旋极化电子结构来解释这些结果。 具体而言，我们报告了局部晶格畸变的大小与空位周围局部电子自旋极化程度之间的耦合。 这导致 Fe 原子松弛到晶格空位中，而 Ni 原子则刚性地固定在其原始晶格位置上。 这种效应在确定 Ni 原子相对于 Fe 原子的迁移率降低中起着关键作用。 这些结果为长期以来的实验观察提供了原子尺度的见解，即 Ni 在 Fe-Ni 合金中表现出显著缓慢的原子扩散。 显示英文摘要

摘要： The mobility of both Fe and Ni atoms in ferromagnetic $\textrm{Fe}_x \textrm{Ni}_{1-x}$ alloys ($0.4 \leq x \leq 0.6$) is investigated within the framework of ab initio electronic structure calculations, using the nudged elastic band (NEB) method to accurately quantify energetic barriers to lattice vacancy migration. Both the atomically disordered ($A1$) fcc phase, as well as the atomically ordered, tetragonal $\textrm{L}1_0$ phase - which is under consideration as a material for a rare-earth-free 'gap' magnet for advanced engineering applications - are investigated. Across an ensemble of NEB calculations performed on supercell configurations spanning a range of compositions and containing disordered, partially ordered, and fully ordered structures, we find that Ni atoms are consistently significantly less mobile than Fe atoms. Crucially, we are able to interpret these findings in terms of the ferromagnetic alloy's underlying spin-polarised electronic structure. Specifically, we report a coupling between the size of local lattice distortions and the magnitude of the local electronic spin polarisation around vacancies. This causes Fe atoms to relax into lattice vacancies, while Ni atoms remain rigidly fixed to their original lattice positions. This effect plays a key role in determining the reduced mobility of Ni atoms compared to that of Fe atoms. These results shed atomic-scale insight into the longstanding experimental observation that Ni exhibits remarkably slow atomic diffusion in Fe-Ni alloys.