Observation of a phase transition within the domain walls of ferromagnetic Co3Sn2S2

TL;DR

This study reveals a two-dimensional phase transition within the domain walls of ferromagnetic Co3Sn2S2, affecting domain wall mobility and magnetization texture, with implications for spin transport and magnetic manipulation.

Contribution

It uncovers a novel 2D phase transition within domain walls of Co3Sn2S2, expanding understanding of domain wall behavior in topological ferromagnets.

Findings

Identification of a deep minimum in domain wall mobility coinciding with anomalies.

Demonstration of a 2D phase transition within domain walls affecting magnetization texture.

Proposal that a giant magnetocrystalline anisotropy quality factor drives this transition.

Abstract

The ferromagnetic phase of Co$_3$Sn$_2$S$_2$ is widely considered to be a topological Weyl semimetal, with evidence for momentum-space monopoles of Berry curvature from transport and spectroscopic probes. As the bandstructure is highly sensitive to the magnetic order, attention has focused on anomalies in magnetization, susceptibility and transport measurements that are seen well below the Curie temperature, leading to speculation that a "hidden" phase coexists with ferromagnetism. Here we report spatially-resolved measurements by Kerr effect microscopy that identify this phase. We find that the anomalies coincide with a deep minimum in domain wall (DW) mobility, indicating a crossover between two regimes of DW propagation. We demonstrate that this crossover is a manifestation of a 2D phase transition that occurs within the DW, in which the magnetization texture changes from continuous rotation to unidirectional variation. We propose that the existence of this 2D transition deep within the ferromagnetic state of the bulk is a consequence of a giant quality factor for magnetocrystalline anisotropy unique to this compound. This work broadens the horizon of the conventional binary classification of DWs into Bloch and N\'eel walls, and suggests new strategies for manipulation of domain walls and their role in electron and spin transport.