Unidirectional anomalous Hall magnetoresistance

We predict a unidirectional anomalous Hall magnetoresistance (UAHMR) effect in bilayer systems composed of a ferromagnetic metal and a nonmagnetic metal, whereby the longitudinal resistance varies when the electric field direction is reversed or the magnetization is rotated. In contrast to the unidirectional spin Hall magnetoresistance (USHMR) [1], the UAHMR does not rely on the spin Hall effect in the nonmagnetic metal layer but instead arises from the anomalous Hall effect in the ferromagnetic layer. An analytical expression of the UAHMR is obtained by solving a set of drift-diffusion equations with proper boundary conditions, which allows us to analyze the dependence of the UAHMR on materials and geometric parameters of the bilayer system. We will also discuss how to distinguish the UAHMR from the USHMR experimentally when both effects are present as well as a new scheme to measure the spin/anomalous Hall angle based on the nonlinear transport effect.

[1] C. O. Avci, K. Garello, A. Ghosh, M. Gabureac, S. F. Alvarado, and P. Gambardella, Nat. Phys., 11, 570 (2015).