拓扑绝缘体/铁磁异质结构中自旋轨道力矩诱导磁化翻转物理机制的研究

Magnetization reversal (switching) is a frontier subject in the field of spintronics, specifically, in topological insulator (TI)/ ferromagnetic (FM) heterostructure, the magnetization switching of the FM layer can be realized by the spin orbit torque (SOT) generated by TI. The magneto-resistive random access memory (MRAM) based on SOT owns unique advantages, such as high reading and writing speed, low energy consumption and high integration, however before entering the utility, many aspects remain unclear and some basic problems are still unsolved, for instance, what is the relative contribution of TI's surface and bulk charge carriers to the SOT generation, how to enhance the transmission and injection of spin current to improve the SOT efficiency, how to regulate and control SOT and so on. In this study we will investigate the physical mechanism of generating SOT by topological insulator, explore the effective methods to improve SOT efficiency, regulate and control the SOT. More specifically, the (Bi1-XSbX)2Te3/CoTb system will be prepared to investigate the relative contribution of TI's surface and bulk charge carriers to the generation of SOT. By introducing Topological Kondo Insulator SmB6 and fabricating SmB6/CoTb heterostructure, the contribution of bulk charge carriers to the generation of SOT can be fully excluded at ultra-low temperature. By inserting the antiferromagnetic insulator NiO between Bi2Se3 and CoTb, and utilizing the magnon and spin fluctuations in the NiO, the spin current transmission and injection could be enhanced, so as improving the SOT efficiency. In order to regulate and control SOT, The TI1/FM/TI2 sandwich structure will be prepared to increase the channel of the spin current injection to the FM layer. Through the above research, we will further understand the physical mechanism of generating SOT by TI, so as to achieve efficient manipulation of the magnetization switching process.

利用拓扑绝缘体（TI）产生自旋轨道力矩（SOT）实现邻近铁磁层（FM）磁化翻转是自学电子学研究的前沿，基于该原理的磁性存储器具有速度快、能耗低和集成度高等优点。但是该领域还有很多重要问题没有解决：TI表面态和体能态载流子对产生SOT的相对贡献，如何通过增强自旋流传输和注入来提高SOT效率，如何调控SOT等。本项目将研究TI产生SOT的机制、提高SOT效率和调控SOT的方法。具体的，调控TI中参与输运的表面体和体能态载流子数目，研究两者对产生SOT的相对贡献。利用拓扑近藤绝缘体极低温下仅表面态导电的特性可以摒除体能态对产生SOT的影响。制备Bi2Se3/NiO/CoTb体系，利用NiO中磁振子和自旋涨落增强自旋流的传输和注入，提高SOT效率。制备TI1/FM/TI2体系，增加向FM层注入自旋流的维度以调控SOT。通过上述研究进一步深入理解TI产生SOT的物理机制，实现高效操控磁化翻转过程。

利用拓扑绝缘体（TI）产生自旋轨道力矩（SOT）实现邻近铁磁层（FM）磁化翻转是自学电子学研究的前沿，基于该原理的磁性存储器具有速度快、能耗低和集成度高等优点。我们利用自旋泵浦铁磁共振，自旋塞贝克效应，非均匀场输运以及克尔显微镜等实验手段研究了提高TI/FM异质结构中自旋流和SOT效率的物理机制。（1）研究了YIG/Bi2Se3中TI表面态对界面交换耦合和各向异性的影响，表面态电子自旋通过类RKKY（Ruderman–Kittel–Kasuya–Yosida）机制间接参与并增强了TmIG中Fe3+之间的交换耦合，从而导致了TmIG垂直磁各向异性的增强。（2）研究了具有不同磁结构的CoTb薄膜对于自旋流的检测机制，自旋流转换效率对Tb组分的依赖关系主要源自自旋霍尔效应的外禀机制。研究了极薄的Py插层对于自旋流注入和传输的影响，Py插层引入了自旋记忆损失，与自旋涨落互相竞争，共同调制了界面的自旋混合电导。（4）采用非均匀磁场研究了CoTb霍尔靶的输运特性，首次实现了大小和极性均可调节反对称磁电阻效应，证明其源自倾斜磁畴壁附近非平衡电流引起的电势重新分布，并证实了反常霍尔系数在反对称磁电阻的调制中起主要作用。（5）通过制备人工亚铁磁体系，利用自选泵浦铁磁共振技术同时实现具有左手和右手手性的磁振子，并证明了磁振子手性是一种独立的本征自由度。