界面轨道力矩激发纳米级太赫兹磁振子
Interfacial orbital torques excite nanoscale terahertz magnons
- University of Konstanz（康斯坦茨大学）
- Uppsala University（乌普萨拉大学）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文构建原子级框架分离界面自旋与轨道力矩贡献，发现界面轨道力矩是激发纳米级太赫兹磁振子的主通道，为磁性多层膜的太赫兹自旋动力学调控提供微观基础。
AI中文摘要：
以交换作用为主的纳米厚度铁磁体中的磁振子，会因垂直驻立自旋波（PSSW）模式的厚度量子化而延伸至太赫兹频段。尽管已有研究证实界面自旋轨道力矩（SOT）可实现此类模式的激发，但界面驱动力矩的微观起源仍不明确，尤其自旋电流与轨道电流共存的情况使相关理解更为复杂。本文构建并运用了一种原子级框架，该框架可明确解析界面对称性，并分离自旋与轨道力矩的贡献。利用非磁性层夹着薄铁磁层的三层结构，界面力矩的对称性控制极性会产生模式选择性磁振子激发，这与Salikhov等人2023年发表于《自然·物理》（Nature Phys. 19, 529）的近期实验观测结果一致，本文据此厘清了不同界面力矩的贡献。通过将力矩分解为磁化偶（类场）分量与磁化奇分量，本文确定类场力矩是负责激发的主要贡献项。关键的是，分离轨道与自旋贡献后发现，界面轨道力矩是薄铁磁体中高效激发以交换作用为主的太赫兹磁振子的主要通道。本文的研究结果为磁性多层膜中受限太赫兹自旋动力学的对称性工程调控奠定了微观基础。
英文摘要：
Exchange-dominated magnons in nanometer-thick ferromagnets extend to the terahertz regime through thickness quantization of perpendicular standing spin-wave (PSSW) modes. While interfacial spin-orbit torques (SOTs) have been shown to enable the excitation of such modes, the microscopic origin of the interfacial driving torque remains unclear. In particular, the coexistence of spin and orbital currents complicates the understanding. Here, we develop and use an atomistic framework that explicitly resolves interfacial symmetries and separates spin and orbital torque contributions. Exploiting a trilayer geometry for a thin ferromagnet sandwiched between non-magnetic layers, where the symmetry-controlled polarity of the interfacial torque produces mode-selective magnon excitation as observed in the recent experiment of Salikhov et al. Nature Phys. 19, 529 (2023), we disentangle the different interfacial torque contributions. By decomposing the torque into magnetization-even (field-like) and magnetization-odd components, we identify the field-like torque as the dominant contribution responsible for the excitation. Crucially, isolating orbital and spin contributions reveals that the interfacial orbital torque provides the primary channel for the efficient excitation of exchange-dominated THz magnons in thin ferromagnets. Our results establish a microscopic basis for symmetry-engineered control of confined terahertz spin dynamics in magnetic multilayers.
