Field-driven phase transition crossover in kagome antiferromagnet Mn$_{3-x}$Co$_x$Sn

Abstract

Mn$_3$Sn exhibits a complex magnetic phase diagram with multiple symmetry-breaking phenomena. Minute electron doping at the Mn site breaks the kagome lattice symmetry in Mn$_3$Sn. In this work, we exploited this to tune the order of the magnetic phase transition using magnetocaloric effect in Mn$_{3-x}$Co$_x$Sn single crystals. Pristine Mn$_3$Sn shows metallic behaviour with a spin-reorientation transition at 278 K, which shifts to 175 K upon Co doping. Additionally, Co doping also induces a weak-ferromagnetic transition near $\approx 210$ K. The effect of Co doping results inverse to conventional magnetocaloric effect, with enhanced magnetic entropy change. Further, the scaled entropy change reveals a field-driven magnetic phase transition crossover from first order to second order in Mn$_{2.75}$Co$_{0.25}$Sn crystal. Based on experimental data, a new phase diagram is constructed, depicting the field evolution of various magnetic orders.