Magnetic memory and distinct spin populations in ferromagnetic Co3Sn2S2

TL;DR

This paper uncovers a memory effect in ferromagnetic Co3Sn2S2 caused by a secondary spin population with a higher coercive field, revealing complex local magnetization behavior and a non-thermodynamic temperature scale.

Contribution

It identifies a distinct secondary spin population responsible for magnetic memory and characterizes the associated non-equilibrium temperature scale in Co3Sn2S2.

Findings

Memory effect persists without large magnetic fields.

Secondary spin population has higher coercive field.

Local magnetization varies drastically, indicating a complex energy landscape.

Abstract

Co3Sn2S2, a ferromagnetic Weyl semi-metal with Co atoms on a kagome lattice, has generated much recent attention. Experiments have identified a temperature scale below the Curie temperature. Here, we find that this magnet keeps a memory, when not exposed to a magnetic field sufficiently large to erase it. We identify the driver of this memory effect as a small secondary population of spins, whose coercive field is significantly larger than that of the majority spins. The shape of the magnetization hysteresis curve has a threshold magnetic field set by the demagnetizing factor. These two field scales set the hitherto unidentified temperature scale, which is not a thermodynamic phase transition, but a crossing point between meta-stable boundaries. Global magnetization is well defined, even when it is non-uniform, but drastic variations in local magnetization point to a coarse energy landscape, with the thermodynamic limit not achieved at micrometer length scales.