自旋转矩效应和Rashba效应所驱动的磁畴壁动力学研究

The spin-transfer torque (STT) effect has attracted great attention in the past several years, in which the orientation of magnetization in nanoscale spintronic devices can be controlled by a spin-polarized current, instead of the conventional magnetic fields. In contrast, the current-mediated Rashba effect in magnetic nanowires with a structural inversion asymmetry (SIA) has recently been reported, which has been suggested to be another key concept for the successful applications in the nonvolatile Race-track memory and spin logic devices based on the controlled movement of domain walls. However, the topic of current-induced Rashba effect in magnetic nanowires only started with two 'Nature Materials' papers published in last year, and so the topic is absolutely novel and many aspects are still unclear. In this project, micromagnetic simulation technique will be employed to study the combined effects of both STT and Rashba in magnetic nanowires caused by spin-polarized current. Firstly, the micromagnetic model of the two effects will be developed. Secondly the influence of Rashba effect, STT and damping factor on the domain-wall velocity will be clarified. Furthermore, the characteristics and varying trends in different types of domain walls including Bloch, Neel and vortex walls will be explored. And finally the optimal structure and materials will be proposed. We are strongly convinced that all these findings will open new insights into the understanding of current-driven domain wall motion and may provide new prospects for applications in advanced spintronic devices.

"自旋转矩（STT）效应"打破了"磁场"操控磁化矢量的传统模式，开创性地提出在纳米自旋电子器件中采用自旋极化电流直接操控磁矩方向，近些年已引起广泛关注。与之相对应，2010年在结构反演非对称(SIA)磁纳米线中新发现的电流诱导的"Rashba效应"是电流调控磁矩转动的又一个关键因素，对开发基于电流驱动磁畴壁移动机理的赛道磁存储器和自旋逻辑器件至关重要。然而有关Rashba效应的物理机理、特性和作用等基础性研究才刚刚起步，亟待深入探讨。本课题拟发展和建立STT效应和Rashba效应并存的 微磁学模型，采用微磁学方法，研究两者关联机制；探讨磁畴壁移动速度与Rashba效应、STT效应、阻尼因子等参数依赖性；揭示Rashba效应驱动不同类型磁畴壁结构（Bloch壁、Neel壁、磁涡旋壁等）的行为特性和规律；进而理论优化磁纳米线器件结构，为发展电流直接驱动的新型自旋电子器件奠定基础。

“自旋转矩 (STT) 效应”的发现打破了传统“磁场”操控磁化矢量方向模式，开创性地实现了采用自旋极化电流直接操控磁矩方向的物理新理念，为开发新型自旋电子器件翻开崭新一页。本课题是针对STT效应和电流诱导的Rashba自旋轨道耦合效应方面开展了系列基础研究，主要取得如下研究成果：（1）我们建立了STT和Rashba两种不同效应所驱动磁畴壁运动的微磁学模型。模拟研究发现，在STT效应单纯作用下，磁畴壁始终呈线性移动；而当STT和Rashba效应共同作用时，磁畴壁出现了一种进退往复的运动特性。（2）我们研究了STT驱动的垂直磁化自旋阀，分析了自旋极化层或自由层磁矩倾斜所导致的磁动力学特性，建立了静态和动态特性所依赖的参数相图。（3）结合第一原理和微磁学,研究了在垂直磁化隧道结中由电压施加在自由层非对称上下界面时通过自旋-轨道耦合作用所诱导的磁各向异性改变，从而影响磁动力学特性，展现出非确定性toggle-like磁化翻转。我们提出采用STT效应和电场相结合的共同驱动模式，发现不仅可有效降低电流能耗约达两个数量级，同时可解决单纯电场驱动时所产生的非确定性翻转问题。（4）我们还研究了两个自旋阀型STT纳米振荡器通过散磁场实现的相位同步问题，以及两个纳米接触STT振荡器的融合问题等。共发表SCI 收录论文20篇（含Physical Review B 3篇; Applied Physics Letters 3篇, Scientific Report 2篇, Nanotechnology 1篇等）.

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