Abstract

The physical properties of Fe₂CoAl (FCA) Heusler alloy are systematically investigated using the first-principles calculations within generalized gradient approximation (GGA) and GGA+U. The influence of atomic ordering with respect to the Wyckoff sites on the phase stability, magnetism and half metallicity in both the conventional L2₁ and XA phases of FCA is focused in this study. Various possible hypothetical structures viz., L2₁, XA-I, and XA-II are prepared by altering atomic occupancies at their Wyckoff sites. At first, we have determined the stable phase of FCA considering various non-magnetic (or paramagnetic), ferromagnetic (FM) and antiferromagnetic (AFM) configurations. Out of these, the ferromagnetic (FM) XA-I structure is found to be energetically most stable. The total magnetic moments per cell are not in agreement with the Slater-Pauling (SP) rule in any phase; therefore, the half-metallicity is not observed in any configurations. However, FM ordered XA-I type FCA shows 78% spin polarization at the Fermi Energy (E_F). Interestingly, the results of XA-I type FCA are closely matched with the experimental results.

Graphical abstract

中文翻译：

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Fe 2 CoAl Heusler合金中L2 1和XA有序的竞争：第一性原理研究

摘要

使用广义梯度近似（GGA）和GGA + U中的第一性原理系统地研究了Fe ₂ CoAl（FCA）Heusler合金的物理性能。这项研究重点研究了FCA的常规L2 ₁和XA相中相对于Wyckoff位点的原子有序性对相稳定性，磁性和半金属性的影响。各种可能的假设结构，即L2 ₁，XA-I和XA-II是通过改变其Wyckoff位点的原子占据来制备的。首先，我们考虑了各种非磁性（或顺磁性），铁磁性（FM）和反铁磁性（AFM）配置来确定FCA的稳定相位。其中，发现铁磁（FM）XA-I结构在能量上最稳定。在任何阶段，每个单元的总磁矩与Slater-Pauling（SP）规则不一致。因此，在任何配置下均未观察到半金属性。然而，FM下令XA-I型FCA显示了在费米能级（E 78％自旋极化_˚F）。有趣的是，XA-I型FCA的结果与实验结果非常吻合。

图形概要