自旋热点主导的超快退磁机制研究

The discovery of ultrafast demagnetization induced by femtosecond laser pulse, not only challenges the understanding of conventional magnetism, but also can increase the speed of magnetization reversal 10 times faster than the existing limit via the excited nonequilibrium state. However, the underlying mechanism of ultrafast demagnetization is unclear. In this proposal, we unveil this longstanding puzzle from the calculations of electronic structure with spin-orbit coupling combined with the simulations of ultrafast magnetization dynamics. The ultimate aim is to explore the mechanism of spin hot spots-mediated ultrafast demagnetization. The detailed investigations include as: (i) Based on the static electronic properties (in particular the band structure), we map out the precise distribution of spin hot spots in momentum space and estimate their respective spin-flip probabilities. (ii) We simulate the ultrafast magnetization dynamics from the Liouville motion equation and extract the demagnetization time and strength. (iii) We construct the scaling law between the dynamic results (the demagnetization time and strength) and the static parameters (spin-flip probabilities) for various magnetic materials, and systematically study the so-called spin hot spots-mediated ultrafast demagnetization. This will give a guide for seeking the better demagnetized material candidates in experiment. Importantly, the research in this project will allow faster magnetic recording applied in future information processing technology.

飞秒激光脉冲诱导的超快退磁不仅改变了人们对传统磁性的认识，而且还能通过激发的非平衡态实现磁化反转速度的数量级提升，但目前其内在的物理机制尚不清楚。本项目以探索飞秒激光脉冲诱导的超快退磁机制为目的，以计入自旋-轨道耦合的电子结构计算结合超快磁化动力学的理论模拟为手段，重点研究自旋热点主导的超快退磁机制。通过静态的电子结构计算，在动量空间中分析自旋热点的分布特征，并计算相应的自旋反转几率α；利用Liouville运动方程动态模拟自旋热点响应飞秒激光脉冲的超快退磁过程，获得相应的退磁时间τD和退磁强度ΔM；针对不同的磁性材料，构建动态模拟结果(τD、ΔM)与静态计算结果(α)之间的标度关系，探索自旋热点主导的超快退磁机制，并以此预测具有较大退磁效应的磁性材料。本项目的实施不仅对实验上寻求更好的退磁候选材料具有指导意义，而且对超快退磁机制在信息处理技术领域的应用提供理论基础。

本项目以探索飞秒激光脉冲诱导的超快退磁机制为目的，在考虑自旋-轨道耦合的基础上，计算材料的电子结构以及超快磁化动力学过程，重点探索动量空间下自旋热点主导的超快退磁机制。通过电子结构计算，在动量空间中分析自旋热点的分布特征，并计算自旋反转几率α；利用Liouville运动方程动态模拟自旋热点响应飞秒激光脉冲的超快退磁过程，获得相应的退磁时间τD和退磁强度ΔM；针对不同的磁性材料，构建了τD与α之间的依赖关系。本项目对实验上寻求更好的退磁候选材料具有指导意义。目前在项目资助下发表已标注SCI论文9篇，其中以本人为第一（或通讯）作者发表论文4篇，授权发明专利2项。期间培养本科毕业生2名，毕业硕士研究生1名，在读研究生9名，参加2019、2021年国内物理学秋季会议，2021年物理学秋季会议作邀请报告。