超短磁脉冲对软磁纳米线畴壁运动调控的研究

New magnetic nano-scale devices based on domain wall motions driven by magnetic field as the recording cells have received considerable attention, due to their advantages of high-speed storage（the velocity of domain wall motion ~1000 m/s order of magnitude）, high density and non-volatile properties et al. However, with the increase of magnetic recording density, how to accurately control the domain wall motion and improve its motion velocity in nanowires are crucial issues in the industry. This project aims to investigate the mechanism of the domain wall motion driven by the magnetic field in the soft magnetic nanowire, and improve its domain wall velocity. Firstly, we plan to modulate the Gilbert damping factor and magnetic anisotropy of the nanowires, meanwhile we will try to control the magnetic domain wall formation and motion process by ultrashort magnetic pulse with various pulse width ranging from hundreds of femtoseconds to tens of picoseconds and strength generated by femto-second laser. Secondly, we also plan to utilize the time-resolved technique to observe the changes of magnetic domain walls in real-time. At the same time, we systematically study the relationship of domain wall motions in nanowires between modulated ultrashort magnetic pulse and nanowires geometry by using micromagnetic simulation. Finally, we plan to investigate the method of accurate control of magnetic nanowires domain wall motion and improvement of domain wall velocity by both the experiments and theory, and fabricate the nanoscale logic device based on the domain wall logic, to provide experimental and theoretical basis for the development of domain wall logic device and magnetic memory device.

磁场驱动畴壁作为记录单元的新型磁性纳米器件具有高速存储（其畴壁迁移速率可达千米/秒量级）、高密度和非易失性等性能。随着磁记录密度的日益增长，信息存入更小的记录单元，需要精确调控磁性纳米器件的畴壁运动及进一步提高其迁移速率。本项目拟研究以软磁纳米线的畴壁为记录单元，探索磁场驱动的磁性纳米线畴壁运动的机制及提高其迁移速率的方法。通过调控磁纳米线的吉尔伯特因子、畴壁宽度和磁各向异性，并利用飞秒激光产生脉宽（亚皮秒至皮秒）和强度可调谐的超短磁脉冲调制磁性纳米线畴壁形成及运动过程；结合时间分辨的探测技术实时观测其微观磁畴的变化规律，运用微磁学模拟,系统研究磁性纳米线的畴壁运动与超短磁脉冲、吉尔伯特因子及纳米线几何构型的调制关系以及相关理论，从实验与理论上探讨精确控制软磁纳米线畴壁高速运动的方法，并制备高读写速度的磁性纳米线逻辑器件，为发展磁性纳米畴壁逻辑和存储器件提供实验及理论依据。

本项目利用飞秒激光激发的皮秒到飞秒时间量级的磁场驱动畴壁运动探讨解决精确控制微纳磁性结构的畴壁运动和提高畴壁运动速度的方法。我们搭建了连续激光和飞秒激光激发的皮秒到飞秒时间量级的光斑聚焦到1微米内的微聚焦时间分辨磁光克尔效应仪，可测量微纳结构的静态磁性及飞秒激光诱导的磁化动力学过程。同时我们制备了不同系列的磁性薄膜，在改变磁性薄膜的构型、厚度和耦合层等制备工艺的基础上，并利用飞秒激光脉冲产生和调制超短磁脉冲，结合时间分辨的微米聚焦磁光克尔效应研究其超快退磁和磁化进动过程，获得了高磁化强度、高进动频率和小吉尔伯特因子的磁性薄膜；通过光刻和电子束刻蚀设备成功制备了与上述不同系列薄膜相应的磁性微纳米结构，在改变磁性结构的尺寸、厚度和构型的制备工艺的基础上，我们通过在磁性微纳米结构局域位置注入飞秒激光脉冲，利用时间分辨磁光光谱研究其磁化动力学过程，获得其退磁时间、进动频率和吉尔伯特因子。通过对磁性微纳米结构的静态磁性和磁化动力学的研究，以及应用理论模型对实验结果进行了探讨，进一步探索了磁各向异性、静磁相互作用和杂散场对磁畴形成的影响。以上工作不仅调控了磁性薄膜及其相应的微纳米结构的超快退磁时间、进动频率和吉尔伯特因子等，并探索了微纳米磁性逻辑器件的最优参数，为发展磁性微纳米器件提供实验以及理论依据。