Ultrafast magnetization enhancement via the dynamic spin-filter effect of type-II Weyl nodes in a kagome ferromagnet
Xianyang Lu, Zhiyong Lin, Hanqi Pi, Tan Zhang, Guanqi Li, Yuting Gong, Yu Yan, Xuezhong Ruan, Yao Li, Hui Zhang, Lin Li, Liang He, Jing Wu, Rong Zhang, Hongming Weng, Changgan Zeng, Yongbing Xu
Abstract
Abstract The magnetic type-II Weyl semimetal (MWSM) Co 3 Sn 2 S 2 has recently been found to host a variety of remarkable phenomena including surface Fermi-arcs, giant anomalous Hall effect, and negative flat band magnetism. However, the dynamic magnetic properties remain relatively unexplored. Here, we investigate the ultrafast spin dynamics of Co 3 Sn 2 S 2 crystal using time-resolved magneto-optical Kerr effect and reflectivity spectroscopies. We observe a transient magnetization behavior, consisting of spin-flipping dominated fast demagnetization, slow demagnetization due to overall half-metallic electronic structures, and an unexpected ultrafast magnetization enhancement lasting hundreds of picoseconds upon femtosecond laser excitation. By combining temperature-, pump fluence-, and pump polarization-dependent measurements, we unambiguously demonstrate the correlation between the ultrafast magnetization enhancement and the Weyl nodes. Our theoretical modelling suggests that the excited electrons are spin-polarized when relaxing, leading to the enhanced spin-up density of states near the Fermi level and the consequently unusual magnetization enhancement. Our results reveal the unique role of the Weyl properties of Co 3 Sn 2 S 2 in femtosecond laser-induced spin dynamics.