锰基反铁磁外延薄膜中拓扑霍尔效应

Very recently, antiferromagnetic spintronics has attracted much attention, as a newly emerging research field. Theoretical studies have extensively shown that Mn3X (X=Pt, Ir, Rh, Ge, Sn, Ga) ordered alloys exhibit large anomalous Hall effect, i.e., topological Hall effect, due to their non-collinear spin structure. In contrast, experimental studies still lack. Accordingly, we will focus on topological Hall effect of L12 ordered IrMn3 and PtMn3 epitaxial films and disordered FeMn, IrMn, PtMn ones. Firstly, we will explore and optimize the fabrication condition of L12 ordered IrMn3 and PtMn3 epitaxial films and disordered FeMn, IrMn, PtMn ones, with the magnetron sputtering and pulse laser deposition techniques. Secondly, we will study the scaling law of the topological Hall effect in these films, by varying the measurement temperature and the film thickness. Finally, ab. initio calculation will also be made in order to deeply understand the physics mechanism of the topological Hall effect from the view point of the electronic band structure near the Fermi level.

最近，反铁磁自旋电子学作为一个新的研究热点备受关注。已有的理论研究表明，Mn3X (X=Pt, Ir, Rh, Ge, Sn, Ga等)非共线反铁磁材料中存在可观的拓扑霍尔电导率，但是缺乏相应的实验研究。本项目拟对L12 IrMn3和PtMn3有序合金外延薄膜，以及FeMn、IrMn、PtMn无序合金外延薄膜中拓扑霍尔效应进行研究。首先，借助于磁控溅射和脉冲激光沉积技术，摸索优化上述外延薄膜的生长工艺条件。在此基础上，通过改变薄膜厚度以及变温测量研究拓扑霍尔效应电阻率与纵向电阻率之间的标度关系。最后结合第一性原理计算，深刻揭示拓扑霍尔效应的电子态物理本质。

反铁磁自旋电子学作为一个新的研究热点备受关注。反铁磁中自旋结构强烈影响其自旋输运性质。本项目围绕非共线反铁磁Mn3Sn和Mn3Pt，以及共线反铁磁L10 MnPd中自旋输运性质开展研究，具体结果如下。（1）利用Mn3Sn中非共线反铁磁产生z自旋流，实现自旋轨道矩驱动高效垂直磁化强度翻转。利用飞秒激光发现Mn3Sn薄膜中光调制的反铁磁序Voigt效应远大于铁磁有序引起的线性磁光克尔效应，并且发现反铁磁序的超快光调控速度在室温以上直至奈尔转变温度区间基本保持恒定。（2）在L12 MnPt中发现反常霍尔效应，其大小与一般铁磁材料相当。（3）研究发现L10 MnPd反铁磁外延薄膜中反常霍尔效应主要来源于表面效应而不是体效应，而表面贡献来源于表面未补偿磁矩，这与Mn3Sn等非共线反铁磁形成鲜明对比。（4）利用L10 FePt有序合金首度确认四度对称的各向异性磁电阻微观机制。