Zhang Wei, He Wei, Peng Li-Cong, Zhang Ying, Cai Jian-Wang, Evans Richard F L, Zhang Xiang-Qun, Cheng Zhao-Hua
State Key Laboratory of Magnetism and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China. School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
Nanotechnology. 2018 Jul 6;29(27):275703. doi: 10.1088/1361-6528/aabdc9. Epub 2018 Apr 12.
The switching of magnetic domains induced by an ultrashort laser pulse has been demonstrated in nanostructured ferromagnetic films. This leads to the dawn of a new era in breaking the ultimate physical limit for the speed of magnetic switching and manipulation, which is relevant to current and future information storage. However, our understanding of the interactions between light and spins in magnetic heterostructures with nanoscale domain structures is still lacking. Here, both time-resolved magneto-optical Kerr effect experiments and atomistic simulations are carried out to investigate the dominant mechanism of laser-induced ultrafast demagnetization in [Co/Pt] multilayers with nanoscale magnetic domains. It is found that the ultrafast demagnetization time remains constant with various magnetic configurations, indicating that the domain structures play a minor role in laser-induced ultrafast demagnetization. In addition, both in experiment and atomistic simulations, we find a dependence of ultrafast demagnetization time τ on the laser fluence, which is in contrast to the observations of spin transport within magnetic domains. The remarkable agreement between experiment and atomistic simulations indicates that the local dissipation of spin angular momentum is the dominant demagnetization mechanism in this system. More interestingly, we made a comparison between the atomistic spin dynamic simulation and the longitudinal spin flip model, highlighting that the transversal spin fluctuations mechanism is responsible for the ultrafast demagnetization in the case of inhomogeneous magnetic structures. This is a significant advance in clarifying the microscopic mechanism underlying the process of ultrafast demagnetization in inhomogeneous magnetic structures.
在纳米结构的铁磁薄膜中，由超短激光脉冲诱导的磁畴切换已得到证实。这开启了一个新时代的曙光，即突破磁开关和操纵速度的最终物理极限，这与当前和未来的信息存储相关。然而，我们对具有纳米级畴结构的磁性异质结构中光与自旋之间相互作用的理解仍然不足。在此，进行了时间分辨磁光克尔效应实验和原子模拟，以研究具有纳米级磁畴的[Co/Pt]多层膜中激光诱导超快退磁的主导机制。研究发现，超快退磁时间在各种磁结构下保持恒定，这表明畴结构在激光诱导的超快退磁中起次要作用。此外，在实验和原子模拟中，我们都发现超快退磁时间τ 与激光能量密度有关，这与磁畴内自旋输运的观测结果相反。实验与原子模拟之间的显著一致性表明，自旋角动量的局部耗散是该系统中的主导退磁机制。更有趣的是，我们对原子自旋动力学模拟和纵向自旋翻转模型进行了比较，突出了横向自旋涨落机制在非均匀磁结构情况下对超快退磁起作用。这在阐明非均匀磁结构中超快退磁过程的微观机制方面取得了重大进展。
