Spin wavepackets in the Kagome ferromagnet Fe$_3$Sn$_2$: propagation and precursors

TL;DR

This study reveals that in Fe$_3$Sn$_2$, spin wavepackets can arrive earlier than expected due to precursors from magnetostatic mode interactions, suggesting new pathways for ultrafast spin transport.

Contribution

It demonstrates the existence of spin wave precursors in a Kagome ferromagnet, challenging the conventional group velocity-based understanding of spin wave propagation.

Findings

Spin wave precursors arrive before $d/v_g$ predicts.

Magnetostatic modes cause the early arrival of spin information.

Implications for ultrafast, long-range spin transport in magnetic systems.

Abstract

The propagation of spin waves in magnetically ordered systems has emerged as a potential means to shuttle quantum information over large distances. Conventionally, the arrival time of a spin wavepacket at a distance, $d$, is assumed to be determined by its group velocity, $v_g$. He we report time-resolved optical measurements of wavepacket propagation in the Kagome ferromagnet Fe$_3$Sn$_2$ that demonstrate the arrival of spin information at times significantly less than $d/v_g$. We show that this spin wave "precursor" originates from the interaction of light with the unusual spectrum of magnetostatic modes in Fe$_3$Sn$_2$. Related effects may have far-reaching consequences toward realizing long-range, ultrafast spin wave transport in both ferromagnetic and antiferromagnetic systems.