拓扑绝缘体表面态自旋轨道矩（SOT）调控研究

The project for the third generation of spin-orbit torque magnetic random access memory (SOT-MRAM), carry out a research about the manipulation of SOT within the surface state of topological insulator. The key scientific issues that need to be solved include: (1) How to prepare high quality topological insulator/ferromagnetic heterojunction, control the Fermi level, and improve interfacial structure? How to enhance the conversion efficiency of charge-to-spin and explain the physical mechanism behind it? (2) How to manipulate the magnetic anisotropy in topological insulator/ ferromagnetic heterojunction? For these problems, we propose a method obtaining high quality topological insulator by magnetron sputtering. Then we study the effect of insertion for improving the interfacial structure, suppressing the reaction at the interface, reducing conductance mismatch, controlling magnetic anisotropy, and reveal the topological insulator/ferromagnetic heterojunctiongrowth mechanism. Simultaneously, we can achieve “rough”, “exquisite”, and “enhanced” manipulation of Fermi level by controlling the proportion of n-type Bi2Te3and p-type Sb2Te3 during deposition, applied gate voltage, and gating with ionic liquid, respectively. Finally, we will figure out the relationship between the Fermi level and the conversion efficiency of charge-to-spinand revealthe connection between the interface behavior, including electronicstructure, atomic structure and interfacial chemical state, and related physical effect especially SOT.

本项目针对自旋轨道矩磁随机存储器SOT-MRAM的技术需求，开展拓扑绝缘体表面态自旋轨道矩（SOT)调控研究。需要解决的科学问题是：如何制备高质量的拓扑/铁磁异质结、控制拓扑绝缘体中费米面的位置、改善界面结构，增强电荷/自旋的转换效率, 有效地调控SOT，阐明其物理机制；如何调控拓扑/铁磁异质结中磁性层的磁各向异性。拟通过磁控溅射方法制备高质量拓扑/铁磁异质结样品，研究插层对改善拓扑/铁磁异质结界面结构、抑制界面反应、减小电导失配和对磁各向异性的影响，揭示其生长机制；在BST薄膜溅射过程中控制n型Bi2Te3和p型Sb2Te3的比例；栅压调控、离子液体调控，分别实现对费米能级的“粗”调、“细”调和“增强”调控，有效地控制拓扑绝缘体薄膜中费米能级位置，弄清费米能级对电荷－自旋流转化效率影响的规律，揭示界面电子结构、原子结构、原子化学状态等界面行为及其与相应物理效应尤其SOT之间的关系。

本项目针对自旋轨道矩磁随机存储器SOT-MRAM的技术需求，开展了拓扑绝缘体表面态自旋轨道矩（SOT）调控研究；揭示界面电子结构、原子结构、原子化学状态等界面行为及其与相应物理效应尤其SOT之间的关系。经该课题实施，研究发现，用磁控溅射方法在热氧化的硅片(300 nm SiO2)上制备大面积的Bi2Te3、(Bi,Sb)2Te3和Cr-(Bi,Sb)2Te3拓扑绝缘体薄膜；通过角分辨光电子能谱(ARPES) 可以观测到Bi2Te3的拓扑表面态，对于Cr掺杂的拓扑绝缘体，在低温下具有蝴蝶型的MR曲线和接近方形的反常霍尔曲线，表明这些薄膜具有易轴垂直于膜面的长程铁磁序。通过栅压调控，可以实现高达16.4 kΩ的反常霍尔电阻和接近0.2的霍尔角。我们还用CMOS兼容的磁控溅射与后退火手段在非晶SiO2/Si衬底上成功生长了性能良好的MnBi2Te4薄膜。另外，我们在轻金属Zr、V的垂直体系Zr/CoFeB/MgO中实现了垂直磁各向异性(PMA)， 并实现了电流驱动的磁化翻转。我们在垂直磁化的Ta/CoFeB/ MgO多层膜体系中通过调控CoFeB/MgO界面处的H+和O2-的行为，使得样品电流诱导磁化翻转所需的Jc仅为单离子（O2-）调控样品的一半。我们还发现界面电荷转移对体系自旋轨道矩有效场的影响，以及Ru掺杂对铁磁薄膜自旋霍尔自旋轨道矩(SOT)效应的影响等等。这些研究成果为自旋电子器件的开发应用提供了重要的科学实验依据。