Magnetic structure of the topological semimetal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Co</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>Sn</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>
Jian-Rui Soh, Changjiang Yi, Ivica Živković, N. Qureshi, A. Stunault, B. Ouladdiaf, J. Alberto Rodríguez‐Velamazán, Youguo Shi, Henrik M. Rønnow, A. T. Boothroyd
Abstract
${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ 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 ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ below ${T}_{\text{C}}=177$ 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 $(\mathbf{k}=\mathbf{0})$ in-plane ${120}^{\ensuremath{\circ}}$ antiferromagnetic order which had previously been considered as a secondary phase present at temperatures between $\ensuremath{\sim}$90 K and ${T}_{\text{C}}$. 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 ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ is a magnetic Weyl semimetal.