Unconventional critical behaviors at the magnetic phase transition of Co3Sn2S2 kagome ferromagnet

TL;DR

This study investigates the unconventional critical behaviors at the magnetic phase transition of Co3Sn2S2, revealing deviations from standard models and suggesting an anomalous magnetic state below the Curie temperature.

Contribution

The paper provides detailed critical behavior analysis of Co3Sn2S2, demonstrating deviations from classical second-order transition models and identifying an anomalous magnetic state.

Findings

Critical exponents do not match standard second-order models.

Magnetization and magnetocaloric effect show deviations from universal curves.

Evidence of an anomalous magnetic state below T_C.

Abstract

Co3Sn2S2 has generated a growing interest as a rare example of the highly uniaxial anisotropic kagome ferromagnet showing a combination of frustrated-lattice magnetism and topology. Recently, via precise measurements of the magnetization and AC susceptibility we have found a low-field anomalous magnetic phase (A-phase) with very slow spin dynamics that appears just below the Curie temperature (T_C). The A-phase hosts high-density domain bubbles after cooling through T_C as revealed in a previous in-situ Lorentz-TEM study. Here, we present further signatures of the anomalous magnetic transition (MT) at T_C revealed by a study of the critical behaviors of the magnetization and magnetocaloric effect using a high-quality single crystal. Analyses of numerous magnetization isotherms around T_C (177 K) using different approaches (the modified Arrot plot, Kouvel-Fisher method and magnetocaloric effect) result in consistent critical exponents that do not satisfy the theoretical predictions of standard second-order-MT models. Scaling analyses for the magnetization, magnetic entropy change and field-exponent of the magnetic entropy change, all consistently show low-field deviations below TC from the universal curves. Our results reveal that the MT of Co3Sn2S2 can not be explained as a conventional second-order type and suggest an anomalous magnetic state below T_C.