标题： 异常霍尔效应和电流自旋极化在Co$_2$FeX (X = Al, Ga, In, Si, Ge, 和 Sn) Heusler化合物中的系统{\it 从头计算}研究 显示英文标题

标题： Anomalous Hall effect and current spin polarization in Co$_2$FeX (X = Al, Ga, In, Si, Ge, and Sn) Heusler compounds: A systematic {\it ab initio} study

摘要： 在本文中，我们对两种主要的自旋相关现象，即异常霍尔效应和电流自旋极化，在基于Co$_2$Fe的Heusler化合物Co$_2$FeX（X = Al，Ga，In，Si，Ge，Sn）中进行了系统的{\it 从头计算}研究，在广义梯度近似（GGA）下进行。使用了精确的全势线性化增广平面波方法。 我们发现，在Co$_2$FeX (X = Al, Ga, In, Al$_{0.5}$Si$_{0.5}$和 Sn) 中纵向电流的自旋极化（$P^L$）为$\sim$100%，尽管费米能级处的电子态（$P^D$）的自旋极化不是。 此外，其他化合物也具有高电流自旋极化，为$P^L > 85$%。 这表明所有考虑的Co$_2$FeX化合物对于自旋输运器件都是有前景的。 有趣的是，$P^D$在Co$_2$FeX（X = Si，Ge和Sn）中为负值，其符号与$P^L$以及传输实验的结果不同。 其次，计算得到的反常霍尔电导率（AHCs）适中，范围在200 S/cm以内，并且与高L2$_1$有序的Co$_2$FeSi样品的可用实验结果吻合良好，尽管它们与其他化合物的报道实验结果存在显著差异，这些化合物中存在B2反位缺陷。 令人惊讶的是，在Co$_2$FeSi中，当Si被Ge取代，最终被Sn取代时，AHC先减小然后改变符号。 第三，除Co$_2$FeSi外，所有研究化合物的计算总磁矩与相应的实验值吻合良好，其中存在0.3$\mu_B$/f.u.的差异。我们还在GGA+$U$方案中进行了GGA加上局域库仑相互作用$U$的计算。我们发现包括$U$显著影响计算得到的总磁矩、自旋极化和AHC，并且在大多数情况下会导致与现有实验结果不一致。 显示英文摘要

摘要： In this paper, we perform a systematic {\it ab initio} study of two principal spin-related phenomena, namely, anomalous Hall effect and current spin polarization, in Co$_2$Fe-based Heusler compounds Co$_2$FeX (X = Al, Ga, In, Si, Ge, Sn) within the generalized gradient approximation (GGA). The accurate full-potential linearized augmented plane-wave method is used. We find that the spin-polarization of the longitudinal current ($P^L$) in Co$_2$FeX (X = Al, Ga, In, Al$_{0.5}$Si$_{0.5}$ and Sn) is $\sim$100 \% even though that of the electronic states at the Fermi level ($P^D$) is not. Further, the other compounds also have a high current spin polarization with $P^L > 85$ \%. This indicates that all the Co$_2$FeX compounds considered are promising for spin-transport devices. Interestingly, $P^D$ is negative in Co$_2$FeX (X = Si, Ge and Sn), differing in sign from the $P^L$ as well as that from the transport experiments. Secondly, the calculated anomalous Hall conductivities (AHCs) are moderate, being within 200 S/cm, and agree well with the available experiments on highly L2$_1$ ordered Co$_2$FeSi specimen although they differ significantly from the reported experiments on other compounds where the B2 antisite disorders were present. Surprisingly, the AHC in Co$_2$FeSi decreases and then changes sign when Si is replaced by Ge and finally by Sn. Third, the calculated total magnetic moments agree well with the corresponding experimental ones in all the studied compounds except Co$_2$FeSi where a difference of 0.3 $\mu_B$/f.u. exists. We also perform the GGA plus on-site Coulomb interaction $U$ calculations in the GGA+$U$ scheme. We find that including the $U$ affects the calculated total magnetic moment, spin polarization and AHC significantly, and in most cases, results in a disagreement with the available experimental results.