基于自旋转矩效应的磁涡核极性翻转研究

项目名称： 基于自旋转矩效应的磁涡核极性翻转研究

项目编号： No.50871075

项目类型： 面上项目

立项/批准年度： 2009

项目学科： 轻工业、手工业

项目作者： 刘要稳

作者单位： 同济大学

项目金额： 34万元

中文摘要： 磁涡旋结构在信息存储和自旋波发生器方面有应用前景，引起人们关注。本项目围绕自旋转矩效应及其如何调控磁涡旋结构的物理机理，开展了微磁学研究，主要取得以下几点成果：（1）建立了磁涡旋参数相图,发现一种"C"态媒介的磁涡核翻转新机制。（2）建立了磁涡核翻转的临界条件，澄清了翻转与脉冲电流强度、宽度的依赖关系，提出实现磁涡核单次翻转的有效控制方案。（3）研究了磁涡核翻转过程中涡核附近的局域能量变化，发现一个局域能量阈值，揭示了"磁涡旋和反涡旋对"的产生和湮灭的机理和起因问题。（4）研究了薄膜圆盘阵列中单元之间的静磁耦合作用及其对磁涡核极性翻转行为特性的影响，探讨了磁耦合作用所导致的磁涡旋本征频谱特性。（5）针对"自旋转矩效应"本身的物理机理，开展了系列研究。提出在垂直磁化自旋阀自由层中"软核"设计可有效降低磁化翻转电流；澄清了阵列结构中静磁耦合效应对磁化翻转的影响；提出自旋阀钉扎层失稳可以诱导自旋转矩回跳翻转。（6）研究了双自旋极化层的自旋转矩效应，以及自旋转矩垂直项作用；首次结合"微磁学"与"从头算第一原理"技术。共发表论文13篇（含APL 4篇，NJP 1篇，PRB 2篇，JAP 3篇）。

中文关键词： 磁涡旋结构；自旋转移矩；微磁模拟；磁性薄膜

英文摘要： Magnetic vortices (MV) have attracted much attention due to their possible applications in data storage and spin wave oscillators. The aim of this project is to address the physical mechanism for manupulation of a vortex core by a spin polarized current through the spin-transfer torque (STT) effect. In the past three years, we have achieved several key progresses as follows: (1) Phase diagram of vortex dependence on the geometric parameters has been estibalished by using micromagnetic simulation technique. We reported a new switching route of the vortex core mediated by a transient C-state. (2) A critical requirement to switch vortex core, which is associated to the current pulse strength and pulse width, has been found. We have theoretically predicted the parameter range of current pulses to achieve a single switching event. (3) We have investigated the energetic aspect of the vortex core switching. The simulations show that the reversal occurs once a well-defined threshold in the exchange energy density is reached. We establish the energetic origin of the core reversal by demonstrating that this threshold corresponds to the energy necessary for creation of a vortex-antivortex pair. (4) The influence of the dynamic dipolar interaction on the current-induced core switch in vortex pairs and arrays has been investigated. It is found that a series of azimuthal spin wave (SW) modes is excited and the high-order harmonics of SW modes are strongly dependent of the core polarities due to the dynamic magnetic interactions between the two vortices. (5) We also carried out a series of studies on the mechanism of STT effect. We find that considerable reduction of the switching current is observed on micromagnetic simulation in a perpendicularly magnetized giant magnetoresistive (GMR) nanopillar with a soft nanocore inside the free layer. The influence of neighboring cells on spin torque switching in a matrix of nanopillars with perpendicular magnetic anisotropy has been clarified. We report that the instability of the reference layer could be responsible for the random events of back hopping to its original direction after successful spin-torque switching. (6) The magnetization switching by dual polarizers and the field-like STT effect have also been demonstrated. A combined ab initio and micromagnetic simulation technique has been tested to build up a direct relationship between critical switching current and geometric structure. We have achieved the goal of this project.

英文关键词： Magnetic vortex; Spin-transfer torque; Micromagnetic simulations: Magnetic thin film