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

Abstract

The interplay between electronic transport and the antiferromagnetic order has attracted a surge of interest. Recent studies have shown that a moderate change in the spin orientation of a collinear antiferromagnet may significantly affect the electronic band structure and subsequently manifest itself in transport properties [1]. Among numerous electrical probes to read out such 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 in the antiferromagnetic phase of a FeRh/Pt bilayer 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, which is in stark contrast with the UMRs observed in ferromagnetic and non-magnetic systems [2-3]. We attribute this UMR 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.This research was primarily supported by the NSF through the University of Illinois at Urbana-Champaign Materials Research Science and Engineering Center DMR-1720633 and was carried out in part in the Materials Research Laboratory Central Research Facilities, University of Illinois. Thin-film growth at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Materials Science and Engineering Division.  Fig. 1: UMR in the antiferromagnetic phase of FeRh [110]/Pt (T = 10 K), as a function of field B at various current densities J.  Fig 2: Generation of a nonlinear charge current transverse to the applied B field (top left), which increases considerably in the presence of canting (bottom right).