发表机构
Nanjing University; Nanjing University of Posts and Telecommunications（南京大学; 南京邮电大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文针对SOT-MRAM传统开关易反向的问题，提出协同STT与SOT的无外场开关方案，通过模拟与解析模型揭示脉冲末端磁化状态是开关速度与可靠性的决定性因素。
AI 中文摘要
自旋轨道转矩磁阻随机存取存储器（SOT-MRAM）是下一代非易失性存储器的领先候选方案，具备高速、高 endurance（ endurance 译为 endurance，即 endurance 性能）及架构兼容性优势。然而，在传统SOT开关中，脉冲终止时磁化强度仍处于面内区域附近，导致最终状态对脉冲后弛豫动力学高度敏感，易发生反向开关。为解决该问题，本文提出一种无外场方案：横向SOT驱动大角度进动激发，同时垂直自旋转移转矩（STT）将轨迹偏向反向-z态。微磁模拟显示，在J_STT-J_SOT参数空间中存在非线性开关边界，源于两种转矩的不同动力学作用：SOT主要控制动力学分界线的激发与穿越，而STT控制终端轨迹与最终状态选择。基于电流诱导平衡稳定性分析的解析宏自旋模型，重现了临界边界随电流密度、吉尔伯特阻尼α及单轴各向异性K_u的变化趋势，并区分了动态反阻尼与静态不稳定分支。对脉冲时长、阻尼、各向异性及STT-SOT平衡的系统分析进一步表明，可靠的超快开关不仅需要在脉冲终止前有足够激发以穿越分界线，还需精确控制脉冲末端磁化状态以最小化脉冲后弛豫。这些结果证实，在耦合STT-SOT系统中，决定开关速度与可靠性的关键因素是脉冲末端状态，而非瞬时转矩幅值。
英文摘要
Spin--orbit torque MRAM (SOT-MRAM) is a leading candidate for next-generation nonvolatile memory, offering high speed, endurance, and architectural compatibility. However, in conventional SOT switching, the magnetization remains near the in-plane region at pulse termination, making the final state highly sensitive to post-pulse relaxation dynamics and prone to back-switching. To overcome this, we propose a field-free scheme in which the transverse SOT drives large-angle precessional excitation while the perpendicular spin-transfer torque (STT) biases the trajectory toward the reversed $-z$ state. Micromagnetic simulations reveal a nonlinear switching boundary in the $J_{\mathrm{STT}}$--$J_{\mathrm{SOT}}$ parameter space, originating from the distinct dynamical roles of the two torques: SOT primarily governs the excitation and crossing of the dynamical separatrix, whereas STT controls the terminal trajectory and final-state selection. An analytical macrospin model, based on the stability analysis of the current-induced equilibrium, reproduces the critical-boundary trends as functions of current density, Gilbert damping $α$, and uniaxial anisotropy $K_\mathrm{u}$, and distinguishes dynamic anti-damping and static instability branches. Systematic analyses of pulse duration, damping, anisotropy, and the STT--SOT balance further demonstrate that reliable ultrafast switching requires not only sufficient excitation to cross the separatrix before pulse termination, but also precise control of the pulse-end magnetization state to minimize post-pulse relaxation. These results establish that the pulse-end state, rather than the instantaneous torque amplitude, is the decisive factor governing switching speed and reliability in coupled STT--SOT systems.
Comments33 pages,6 figures
