自旋转移矩微波发生器的最优构型的理论分析及模拟

Spin-transfer torque (STT) effect, employing spin-polarized current to manipulate the magnetization vectors of the magnetic nanostructures, has been attracting a great deal of attention and research after its prediction and verifications in about 2000s. The nano-scale microwave oscillator based on the STT effect has largely exploited recently since the new solid microwave generator will have great competitiveness and wide applications in future. However, high spin-polarized current threshold and low microwave output power are the main bottlenecks which hinder the spin-transfer oscillators (STOs) from laboratory to industy. How to optimize the configuration of the STO devices, for lowering the current threshold, enhancing the output power and easily adjusting microwave frequency, is still an unclear but important scientific problem. In this project, we plan to study these issues theoretically and numerically based on the modified magnetization dynamics equations with the STT effect terms. We plan to combine the STT induced oscillation research with the nonlinear physics theories such as limit cycle oscillation, synchronization, bifurcation into chaos etc. We plan to explore and obtain the optimized geometric configuration for the STOs, so that one can know how to select and manipulate the physical parameters to realize the aims of lowering the current threshold, enhancing power output, less energy consumption and frequency adjustment. We hope that our theoretical studies can provide important theoretical criterion and reference for the STO microwave nano-devices realization and industrial applications.

自旋转移矩效应（Spin transfer torque，STT）驱动的微波振荡器作为新一代纳米尺度固体微波发生器件极具竞争力和拥有广泛的应用前景，因此近年来备受科研人员的广泛研究。如何选择优化的器件构型，从而降低启动的自旋极化电流，增强微波输出功率，调节微波频率范围，是一个不甚明朗的科学问题。本项目拟从基于带有自旋转移力矩的磁动力学方程出发，结合非线性科学中的极限环振荡，同步，分叉进入混沌等已有理论，理论分析和数值模拟探索找到STT振子的最优化的几何结构构型，从而在降低启动电流，增强功率输出，减少能耗，调节微波频率范围等方面实现电流对磁矩自旋的调控，从而为今后自旋转移矩微波发生器的器件实现和工业应用提供重要的理论依据。

自旋转移矩（Spin transfer torque，STT）效应驱动的微波振荡器作为新一代纳米尺度固体微波发生器件极具竞争力和拥有广泛的应用前景。在本项目中，我们首先研究了单个自旋转移矩微波发生器的最优化几何结构构型问题，获得了在一般倾斜极化构型下的自旋阀结构中磁矩定态解的精确解析表达式，进而提出了具有较低启动电流和较短翻转时间的近似优化构型。我们研究了外部的椭圆双频偏振微波对磁体翻转的调控作用，获得了微波振幅和频率对临界翻转磁场的降低结论。课题组接着研究了具有自旋轨道耦合作用的Dzyaloshinskii-Moriya interaction（DMI）下的磁纳米线中磁畴壁在外场驱动或热驱动下的运动问题，获得了畴壁运动速度的精确及近似解析表达式，进而获得了畴壁运动速度与DMI强度的依赖关系。课题组还采用微磁学oommf模拟软件研究了磁纳米线中缺口对畴壁运动去钉扎场的影响问题以及两个磁体间由于磁偶极相互作用的同步稳定翻转问题。本项目获得的所有结果对于今后自旋转移矩驱动的磁矩翻转，畴壁运动的微波发生器的器件实现和工业应用能提供一定的理论参考价值。