Fe-doping modulated critical behavior and magnetocaloric effect of magnetic Weyl Co3Sn2S2

Abstract

${\mathrm{Co}}_{2.5}{\mathrm{Fe}}_{0.5}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ single crystal was grown by a flux method, and its magnetocaloric effect and critical behavior were systematically investigated. Significant changes in magnetic properties and critical behavior were observed in Fe-doped ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$, compared with undoped ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$. Specifically, the magnetization of ${\mathrm{Co}}_{2.5}{\mathrm{Fe}}_{0.5}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ measured at a low magnetic field ($H<500$ Oe, $H\ensuremath{\parallel}c$ axis) does not show the thermal hysteresis phenomenon, whereas it was observed in ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ near ${T}_{\mathrm{c}}$, which is characteristic of a typical second-order phase transition. Previous reports usually attribute the suppression of ferromagnetism by the substitution of Fe for Co to the decrease in the number of $3d$ electrons. Herein, according to the first-principles calculation, the magnetic moments of dopant Fe align antiparallelly to those of Co atoms, which is also the possible reason for the decrease in magnetization. The critical behavior analysis shows that the critical exponents of the Fe-doped sample around magnetic transition are very close to theoretical values of the mean-field model. Furthermore, the exchange interaction distance $J(r)\ensuremath{\approx}{r}^{\ensuremath{-}4.65}$ and the Rhodes-Wolfarth ratio (RWR) (RWR > 1) prove the long-range itinerant ferromagnetism. The hybridization between the $3d$ orbitals of Fe/Co and the orbitals of $\mathrm{Sn}\text{\ensuremath{-}}5p/\mathrm{S}\text{\ensuremath{-}}3p$ may be an important factor for long-range itinerant ferromagnetism. The zero-field cooling magnetization ($H=100$ Oe, $H\ensuremath{\parallel}\phantom{\rule{0.16em}{0ex}}ab$ plane) undergoes the spin reorientation around 76 K, maybe because the magnetic moments of Fe, aligning antiparallelly to moments of Co atoms, reorient from out of plane to in plane. The critical behavior analysis shows that the first-order phase transition may occur below ${T}_{\mathrm{c}}$ in the case of the $H\ensuremath{\parallel}\phantom{\rule{0.16em}{0ex}}ab$ plane.