磁性纳米结构中由激光引起的超快自旋动力学研究

Laser-induced ultrafast spin dynamics research on magnetic nanostructures

以单个磁性中心的NiO以及由Co和Ni等元素构成的双磁性中心的纳米结构为例,总结了近年所做的主要工作.为了在理论上实现磁性纳米结构中的超快自旋翻转和转移,提出了一种称为Λ进程(Λprocess)的超快自旋转换机理.在实际计算中,首先采用量子化学第一性原理计算得到磁性纳米结构中精确的隙间d电子态,然后考虑外加磁场和自旋轨道耦合分析磁性原子中的自旋局域化程度,最后引入激光脉冲项,研究在其作用下材料的自旋态经由Λ进程实现转换的时间历程.研究结果表明自旋翻转和转移可以在线偏振光的作用下在亚皮秒的时间尺度内完成.为了进一步实现对磁性分子自旋操控的检测和监控,采用附加于磁性中心上的CO分子对磁性分子进行标记.计算得到的与自旋态相关的C—O键振动频率表明自旋操控可以较容易地经由红外光谱实验间接监控.

In this paper,taking one-magnetic-center NiO and two-magnetic-center nanostructures composed of Co and Ni as examples,we review our recent works in this field. To theoretically achieve ultrafast spin flip and transfer in magnetic nanostructures,an ultrafast spin dynamics mechanism,namely Λ process,was proposed. To properly simulate the laser-matter interaction,the accurate intragap d-states were predicted firstly through quantum chemistry calculations; then the spin localizations on magnetic atoms were analyzed considering external magnetic field and spin-orbit coupling; at last, laser pulse term was turned on to study the time history of the spin switching scenario via the Λ process. It was shown that spin flip and transfer can be achieved in a subpicosecond regime with linearly polarized light. In order to further realize checking and monitoring of the spin manipulations in magnetic molecules,a CO molecule was attached to one magnetic center to serve as an infrared marker. The calculated spin-state-dependent C-O stretching frequencies indicate that spin manipulations can be indirectly monitored through infrared spectrum experiments.