飞秒脉冲激光激励下亚铁磁合金薄膜的超快磁动力学研究

Laser-induced magnetization dynamics in rear-earth (RE)-transient-metal (TM) alloys has attracted great attention in the past several years. What has particular interesting is that the ultrafast magnetization switching within several tens of femtoseconds and even faster has been reported recently by means of femtosecond laser pulses, which has high potential for future ultrafast data-storage applications. The laser provides either the heating effect via energy transfer or the switching field via the inverse Faraday effect. However,the microscopic understanding of the underlying processes of such an optically induced magnetization reversal are just getting started, and some deep insights of the mechanism are still unclear. In this project, such a frontier scientific issue will be studied by using an in-house developed micromagnetic simulation technique. The difference of magnetic dynamics between the TM atoms and RE atoms will be firstly clarified. Then, we will focus on the characteristics and the mechanism of the heating effect and inverse Faraday effect, which shall identify the different contributions of the two effects for the laser-induced switching. Finally, we will study the intrinsic damping of the RE-TM amorphous films. We expect the proposed study shall open new insights into the understanding of laser-induced ultrafast magnetization dynamics and provide significant development in spintronics.

脉冲激光激励下"稀土-过渡金属"亚铁磁薄膜的超快磁动力学研究近些年引起广泛关注。特别是近期报道的由飞秒激光在几十飞秒甚至更短的时间内可以驱动磁化翻转的实验成果，有望在未来超快磁存储技术中得到重要应用；其中磁化强度的翻转可以通过飞秒激光提供的"热效应"，或是圆偏振光通过"逆法拉第效应"产生翻转磁场来实现。但有关上述两种磁翻转的微观物理机制目前尚处于起步研究阶段，有待深入探讨。本项目我们将针对这一前沿科学问题开展研究，借助我们自行开发的微磁学模拟程序，研究激光驱动的稀土原子和过渡金属原子之间的磁动力学差异；揭示脉冲激光诱导的热效应和逆法拉第效应的行为特性和微观机理，进而区分两效应在激光驱动磁化翻转过程中的贡献；研究亚铁磁材料的内稟阻尼特性。我们期望这一研究将有助于加深对激光驱动超快磁动力学的理解，推动自旋电子学的发展。

如何实现超快磁翻转是磁学界努力探索的一个基本科学问题。脉冲激光在“稀土-过渡金属（RE-TM）”合金亚铁磁材料中可以实现皮秒量级的超快磁翻转，有望开启飞秒激光诱导超快磁记录技术的发展。本项目针对飞秒脉冲激光激励下亚铁磁合金薄膜的超快磁动力学开展了一些基础研究，主要取得如下研究成果：（1）我们建立和完善了用于描述RE-TM亚铁磁薄膜材料的原子尺度微磁学模型，实现了大尺度薄膜的模拟计算。（2）研究了TbFe薄膜的居里温度Tc和磁补偿点温度随Tb含量的变化特性，以及脉冲激光导致的超快退磁和磁恢复过程。建立了GdFe/TbFe软硬磁复合薄膜的垂直交换耦合模型，研究了其交换偏置特性。（3）研究了激光热效应驱动的亚铁磁材料的磁翻转特性，证实了瞬间铁磁态是实现RE-TM体系磁化翻转的一个重要环节；研究了圆偏振激光通过逆法拉第效应所激发的脉冲磁场模型，研究了不同旋性的圆偏振激光驱动的亚铁磁合金薄膜的磁矩翻转动态过程。（4）此外我们还研究了自旋转矩效应相关的的微磁学研究。共发表SCI论文20篇（含Phys. Rev. Appl.1篇，Phys.Rev.B 3篇; Appl. Phys. Lett. 1篇；New J. Phys. 1篇；J. Magn. Magn.Mater.2篇，Nanotechnology 1篇等）。