Spin-orbitronics in epitaxial CuMnSb/NiMnSb half-Heusler heterostructures

本课题将研究由半heusler合金CuMnSb（反铁磁，AFM）和NiMnSb（铁磁，FM）组成的异质结构中自旋轨道转矩（SOT）相关效应。这种自旋轨道转矩来源于电荷电流在通过具有强自旋轨道耦合（SOC）的材料时发生自旋极化。对于铁磁或反铁磁SOC材料，这种自旋极化与磁矩局部相互作用。这个利用自旋轨道扭矩的实验领域最近被称为“自旋轨道电子学”。作为第一步，我们将进一步开发和优化高晶体质量的分子束外延生长工艺。单层CuMnSb将生长在InAs（001）衬底上；在InP（001）衬底上生长出CuMnSb与NiMnSb结合的异质结构。长大后的样品将主要通过x射线衍射来表征晶体性质和质量，以及通过SQUID来确定磁性参数。在NiMnSb/CuMnSb异质结构中，FM和AFM之间的交换耦合将受到特别关注。对于电气特性，将使用光学光刻技术对标准霍尔杆几何形状进行图像化。在这里，我们将确定材料参数，如电阻率或霍尔常数。利用自旋轨道转矩的几个实验将进行：1)单层外延CuMnSb将用于演示原子力显微镜磁性亚晶格的开关。通过各向异性磁电阻（AMR），我们将能够探测磁亚晶格的方向。2)在第二套器件中，我们将结合AFM CuMnSb和溅射沉积的铁磁薄膜。在这里，我们的主要目标是使用AFM和交换耦合中产生的自旋轨道扭矩来切换FM的磁化。3)对于最终器件，将采用完全外延的NiMnSb/CuMnSb异质结构来制作隧道各向异性磁阻器件。这些装置提供了利用交换弹簧效应在磁输运实验中研究CuMnSb磁特性的可能性。

In this project spin-orbit torque (SOT) related effects in heterostructures comprised of the half-Heusler alloys CuMnSb (antiferromagnetic, AFM) and NiMnSb (ferromagnetic, FM) will be investigated. Such spin-orbit torques originate from charge currents that get spin polarized when passing through materials with strong spin-orbit coupling (SOC). For ferromagnetic or antiferromagnetic SOC materials, this spin polarization interacts locally with the magnetic moments. This field of experiments that takes advantage ofthe spin-orbit torque is recently called “spin-orbitronics”.As a first step a molecular beam epitaxy growth process for high crystal quality CuMnSb will be further developed and optimized. Single layers of CuMnSb will be grown on InAs (001) substrates; heterostructures of CuMnSb combined with NiMnSb will be grown on InP (001) substrates. As grown samples will be mainly characterized by X-Ray diffraction for crystal properties and quality, as well as by SQUID to determine magnetic parameters. In NiMnSb/CuMnSb heterostructures, the exchange coupling between the FM and the AFM will be of special interest. For electrical characterization a standard hall-bar geometry will be patterned using optical lithography. Here, we material parameters will be determined, such as resistivity or Hall-constant. Several experiments that make use of the spin-orbit torque will be conducted: 1) Single layers of epitaxial CuMnSb will be used to demonstrate switching of the magnetic sublattice of the AFM. Via the anisotropic magnetoresistance (AMR), we will be able to probe the orientation of the magneticsublattice. 2) In a second set of devices, we will combine AFM CuMnSb and ferromagnetic films deposited by sputtering. Here, our main goal is to switch the magnetization of the FM using the spin-orbit torque created in the AFM and the exchange coupling. 3) For the final devices, fully epitaxial NiMnSb/CuMnSb heterostructures will be used to fabricate tunneling anisotropic magnetoresistance devices. These devicesoffer the possibility to investigate magnetic characteristics of the CuMnSb in a magnetotransport experiment by making use of the exchange spring effect.