Unidirectional spin Hall magnetoresistance in ferromagnet/normal metal bilayers

TL;DR

This paper reports a unidirectional magnetoresistance effect in ferromagnet/normal metal bilayers caused by spin Hall effects, enabling control and detection of magnetization switching in spintronic devices with simple two-terminal setups.

Contribution

It demonstrates a novel unidirectional magnetoresistance in bilayers due to spin Hall effects, providing a new method for controlling and detecting magnetization in spintronics.

Findings

Resistance changes with current and magnetization reversal.

Effect scales linearly with current density.

Opposite signs in Ta and Pt bilayers.

Abstract

Magnetoresistive effects are usually invariant upon inversion of the magnetization direction. In noncentrosymmetric conductors, however, nonlinear resistive terms can give rise to a current dependence that is quadratic in the applied voltage and linear in the magnetization. Here we demonstrate that such conditions are realized in simple bilayer metal films where the spin-orbit interaction and spin-dependent scattering couple the current-induced spin accumulation to the electrical conductivity. We show that the longitudinal resistance of Ta|Co and Pt|Co bilayers changes when reversing the polarity of the current or the sign of the magnetization. This unidirectional magnetoresistance scales linearly with current density and has opposite sign in Ta and Pt, which we associate with the modification of the interface scattering potential induced by the spin Hall effect in these materials. Our results suggest a route to control the resistance and detect magnetization switching in spintronic devices using a two-terminal geometry, which applies also to heterostructures including topological insulators.