Unidirectional Magnetoresistance in Antiferromagnet/Heavy-metal bilayers

TL;DR

This paper reports the first observation of unidirectional magnetoresistance (UMR) in an antiferromagnetic bilayer, showing significant field-dependent effects and potential for spintronics applications.

Contribution

It demonstrates the existence of UMR in antiferromagnets and explains its origin through field-induced spin canting and Fermi surface distortion.

Findings

UMR observed in FeRh|Pt bilayer with sign change under magnetic field.

UMR magnitude increases by two orders of magnitude with field.

Rashba spin-orbit coupling alone cannot account for the observed UMR.

Abstract

The interplay between electronic transport and antiferromagnetic order has attracted a surge of interest as recent studies have shown that a moderate change in the spin orientation of a collinear antiferromagnet may have a significant effect on the electronic band structure. 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 a UMR in the antiferromagnetic phase of a FeRh$|$Pt bilayer, which undergoes a sign change and then increases strongly with an increasing external magnetic field, in contrast to UMRs in ferromagnetic and nonmagnetic systems. We show that Rashba spin-orbit coupling alone cannot explain the sizable UMR in the antiferromagnetic bilayer and that field-induced spin canting distorts the Fermi contours to greatly enhance the UMR by two orders of magnitude. Our results can motivate the growing field of antiferromagnetic spintronics, and suggest a route to the development of tunable antiferromagnet-based spintronics devices.