The magnetic structure of the topological semimetal Co$_3$Sn$_2$S$_2$

TL;DR

This study uses neutron diffraction and magnetization data to confirm ferromagnetic order in Co$_3$Sn$_2$S$_2$, supporting its classification as a magnetic Weyl semimetal with no evidence of complex antiferromagnetic phases.

Contribution

It provides experimental evidence clarifying the magnetic structure of Co$_3$Sn$_2$S$_2$, confirming ferromagnetic order and ruling out certain antiferromagnetic phases, thus supporting its topological semimetal properties.

Findings

Ferromagnetic order with spins along the c axis confirmed.

No evidence of in-plane 120° antiferromagnetic order.

Discontinuous change at 125 K due to domain size reduction.

Abstract

Co$_3$Sn$_2$S$_2$ has recently been predicted to be a Weyl semimetal in which magnetic order is key to its behavior as a topological material. Here we report unpolarized neutron diffraction and spherical neutron polarimetry measurements, supported by magnetization and transport data, which probe the magnetic order in Co$_3$Sn$_2$S$_2$ below $T_\textrm{C} = 177$ K. The results are fully consistent with ferromagnetic order in which the spins on the Co atoms point along the crystal $c$ axis, although we cannot rule out some canting of the spins. We find no evidence for a type of long-ranged $(\textbf{k}=\textbf{0})$ in-plane 120$^\circ$ antiferromagnetic order which had previously been considered as a secondary phase present at temperatures between $\sim$90 K and $T_\textrm{C}$. A discontinuous change in bulk properties and neutron polarization observed at $T = 125$ K when samples are cooled in a field and measured on warming is found to be due to a sudden reduction in ferromagnetic domain size. Our results lend support to the theoretical predictions that Co$_3$Sn$_2$S$_2$ is a magnetic Weyl semimetal.