Unraveling the origin of the peculiar transition in the magnetically ordered phase of the Weyl 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>
Ivica Živković, Ravi Yadav, Jian-Rui Soh, Changjiang Yi, Youguo Shi, Oleg V. Yazyev, H. M. Rønnow
Abstract
The recent discovery of topologically nontrivial behavior in ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ stimulated a notable interest in this itinerant ferromagnet (${T}_{\mathrm{C}}=174$ K). The exact magnetic state remains ambiguous, with several reports indicating the existence of a second transition in the range 125--130 K, with antiferromagnetic and glassy phases proposed to coexist with the ferromagnetic phase. Using detailed angle-dependent dc and ac magnetization measurements on large, high-quality single crystals we reveal a highly anisotropic behavior of both the static and dynamic response of ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$. It is established that many observations related to sharp magnetization changes when $B\ensuremath{\parallel}c$ are influenced by the demagnetization factor of a sample. On the other hand, a genuine transition has been found at ${T}_{\mathrm{P}}=128$ K, with the magnetic response being strictly perpendicular to the $c$ axis and several orders of magnitude smaller than for $B\ensuremath{\parallel}c$. Calculations using density-functional theory indicate that the ground state magnetic structure consist of magnetic moments canted away from the $c$ axis by a small angle ($\ensuremath{\sim}1.{5}^{\ensuremath{\circ}}$). We argue that the second transition originates from a small additional canting of moments within the kagome plane, with two equivalent orientations for each spin.