Observation of unidirectional magnetoresistance in collinear-antiferromagnet/heavy-metal bilayers*

The interplay between electronic transport and the antiferromagnetic order has attracted a surge of interest. Among numerous electrical probes to read out magnetic order, unidirectional magnetoresistance (UMR), where the resistance changes under the reversal of the current direction, can provide rich insights into the transport properties of spin-orbit coupled systems. However, UMR has never been observed in antiferromagnets before, given the absence of intrinsic spin-dependent scattering. Here, we report that a sizable UMR can emerge in an antiferromagnetic system, specifically in a collinear-antiferromagnet/heavy-metal bilayer. The observed UMR evolves nonlinearly with increasing magnetic field, persists to large values at high magnetic field and, most notably, exhibits a sign change at a critical field, unlike the UMRs observed in ferromagnetic and non-magnetic systems. We attribute a UMR in the antiferromagnetic phase of a FeRh/Pt bilayer to the strong effective magnetic field due to spin canting in FeRh. Our results can motivate the growing fields of non-centrosymmetric and topological systems, and suggest a route to the development of tunable antiferromagnet-based spintronics devices.