超快自旋动力学:从飞秒磁学到阿秒磁学

Ultrafast spin dynamics:From femtosecond magnetism to attosecond magnetism

超快自旋动力学是研究材料受到外场激发后,在皮秒至阿秒时间尺度下其自旋的运动行为.随着激光技术的不断提升,1996年开始的飞秒磁学成为磁学中的重要研究领域,是实现更快响应的新型自旋电子学器件的重要技术途径.尽管已有几十年的历史,飞秒磁学依旧存在着非常多的物理问题尚未解决,而理解这些问题需要研究更快时间尺度下的自旋动力学过程.利用阿秒激光脉冲与磁性材料的相互作用,可研究亚飞秒乃至阿秒时间尺度下、元素分辨的自旋动力学行为,即阿秒磁学.本文介绍了超快自旋动力学近年来的一些重要研究进展以及存在的问题,阿秒磁学研究的机遇与挑战,并对超快自旋动力学的未来发展趋势及前景进行分析与展望.

Ultrafast spin dynamics is the study of the evolution of spin degrees of freedom on a time scale from picoseconds to attoseconds after being excited by an external field.With the development of laser technology,ultrafast spin dynamics has presented new opportunities for realizing ultrafast spintronic devices since 1996.However,despite decades of development,many aspects of femtosecond magnetism remain unclear.Understanding the parameters of these ultrafast spin dynamics processes requires experiments on an even faster timescale.Attosecond magnetism and the interaction of attosecond laser pulses with magnetic materials can reveal spin dynamics on a sub-femtosecond to attosecond time scale.In this review,we first introduce the significant research progress,including the mechanisms of ultrafast demagnetization,all-optical switching,ultrafast spin currents,and terahertz waves.Secondly,we analyze the problems in ultrafast spin dynamics,such as the unclear physical mechanisms of ultrafast demagnetization,the uncertain relationship between magnetic damping and ultrafast demagnetization time,and the unexplored anisotropic ultrafast demagnetization.Thirdly,we discuss the opportunities and challenges in attosecond magnetism.Finally,we analyze and discuss the future development and prospects of ultrafast spin dynamics.