Topological Magnetic Hysteresis in Single Crystals of CeAgSb2 Ferromagnet

TL;DR

This paper reports the discovery of topological magnetic hysteresis in single crystals of CeAgSb2, caused by irreversible changes in magnetic domain topology between closed and open patterns, revealing a new form of magnetic hysteresis.

Contribution

It demonstrates the existence of topological magnetic hysteresis in bulk single crystals, a phenomenon previously observed mainly in thin films or superconductors, highlighting the role of domain topology in magnetic behavior.

Findings

Observation of rectangular tubular ferromagnetic domains in CeAgSb2

Irreversible transition from closed to open domain topology upon field cycling

Identification of topological magnetic hysteresis as a new magnetic phenomenon

Abstract

Closed-topology magnetic domains are usually observed in thin films and in an applied magnetic field. Here we report the observation of rectangular cross-section tubular ferromagnetic domains in thick single crystals of CeAgSb2 in zero applied field. Relatively low exchange energy, small net magnetic moment, and anisotropic in-plane crystal electric fields lower the domain wall energy and allow for the formation of the closed-topology patterns. Upon cycling the magnetic field, the domain structure irreversibly transforms into a dendritic open-topology pattern. This transition between closed and open topologies results in a "topological magnetic hysteresis" - the actual hysteresis in magnetization, not due to the imperfections and pinning, but due to the difference in the pattern morphology. Similar physics was suggested before in pure type-I superconductors and is believed to be a generic feature of other nonlinear multi-phase systems in the clean limit.