自旋轨道耦合对铁磁金属薄膜中反常霍尔效应的调控作用

Since the mechanism of the anomalous Hall effect (AHE) in magnetic films is the same as or similar to those of the new spin related transport phenomena such as spin Hall effect, it has received renewed interest. Previous theoretical and experimental studies have shown that there are three different contributions to the AHE. The intrinsic contribution is caused by the anomalous transverse velocity of electrons. The second skew and third side-jump ones are caused by the asymmetric scattering near the impurity. Although all three contributions are generally believed to be strongly related to the spin orbital coupling (SOC), there almost is no investigation about the SOC effect on the AHE. In particular, there is no direct experimental evidence. Accordingly, we propose to make L1(0) XPdPt (X=Fe, Co,Ni) alloy films on MgO(001) single substrates by DC magentron sputtering. The longitudnal resistivity and Hall one are measured by four point approach at different temerpatures. By changing the concentration ratio of Pt/Pd atoms, the SOC strength can be modified greatly. In this way, the SOC effect on the AHE can be studied and revealed. With ab initio calculations, the effect of SOC and impurity scattering on the skew and side-jump contributions to the anomalous Hall conductivity can be addressed.At the same time, the SOC effect on the normal Hall effect is studied.

磁性薄膜中反常霍尔效应AHE与自旋霍尔效应等新的自旋输运现象具有相同或相似的物理机制，因而近年来备受关注。已有的理论和实验研究表明，AHE存在三种机制，分别来源于传导电子横向反常速度引起的内禀贡献，杂质散射引起的skew和side-jump贡献。虽然人们普遍知道这三种机制都与自旋轨道耦合(SOC)强度密切相关，但是一直缺乏相应的研究，特别缺乏直接的实验研究。基于上述思路，我们提出用磁控溅射方法在MgO(001)单晶衬底上制备L1(0)XPdPt(X=Fe,Co,Ni)三元有序合金外延薄膜，用四探针方法测量薄膜在不同温度下的纵向电阻率和霍尔电阻率。通过改变Pt/Pd的相对原子百分比，大幅度调节自旋轨道耦合强度(SOC)，研究SOC对反常霍尔电导率的影响。结合第一性原理计算，揭示SOC以及杂质散射对 side-jump和skew 贡献的影响机制。同时研究SOC 对正常霍尔效应的影响机制。

自旋轨道耦合是影响材料基本磁性的因素之一。我们系统研究了MgO(001)单晶衬底上制备的L1(0)FePdPt三元有序合金外延薄膜中自旋轨道耦合对磁各向异性、反常霍尔效应、磁性阻尼、磁光效应的影响机制，取得了一些有意义的研究结果。反常霍尔电阻率可以用纵向电阻率的线性项和平方项表述，其中系数分别为a和b。对于反常霍尔效应中与散射无关的反常霍尔电导率b（side-jump的贡献和內禀贡献之和），随着Pt/Pd原子百分比增加而增加。而系数a呈现非单调变化。同时，线性项系数a和平方项系数b可以很好地用1/d的线性函数拟合。研究发现，无序合金薄膜中诱导单轴磁各向异性也随原子百分比增加而增加。另外，我们还研究了自旋轨道耦合对PdPt合金外延薄膜中自旋霍尔效应的影响，发现自旋霍尔角随Pt含量而非单调变化。这说明自旋霍尔角的本征贡献随Pt含量增加而增加，非本征贡献在50 at%Pt含量附近呈现最大值。最后，我们还研究了CoNi合金磁性阻尼与态密度的关系。