Sign reversal of anomalous Hall conductivity and magnetoresistance in cubic non-collinear antiferromagnet Mn$_3$Pt thin films

Abstract

The two dimensional kagome spin lattice structure of Mn atoms in the family of Mn$_3$X non-collinear antiferromagnets are providing substantial excitement in the exploration of Berry curvature physics and the associated non-trivial magnetotransport responses. Much of these studies are performed in the hexagonal systems, mainly Mn$_3$Sn and Mn$_3$Ge, with the kagome planes having their normal along the [001] direction. In this manuscript, we report our study in the cubic Mn$_3$Pt thin films with their kagome planes normal to the [111] crystal axis. Our studies reveal a hole conduction dominant Hall response with a non-monotonic temperature dependence of anomalous Hall conductivity (AHC), increasing from 9 $\Omega^{-1}$cm$^{-1}$ at room temperature to 29 $\Omega^{-1}$cm$^{-1}$ at 100 K, followed by a drop and unexpected sign-reversal at lower temperatures. Similar sign reversal is also observed in magnetoresistance measurements. We attribute this sign reversal to the transition from a Berry curvature dominated AHC at high temperature to a weak canted ferromagnetic AHC response at lower temperature, below 70 K, caused by the reorientation of Mn moments out of the kagome plane. Our above results in thin films of Mn$_3$Pt make advances in their integration with room temperature antiferromagnetic spintronics.