We studied the magnetoresistance of normal metal (NM)/ferromagnet (FM) bilayers in the linear and nonlinear (current-dependent) regimes and compared it with the amplitude of the spin-orbit torques and thermally induced electric fields. Our experiments reveal that the magnetoresistance of the heavy NM/Co bilayers (NM = Ta, W, Pt) is phenomenologically similar to the spin Hall magnetoresistance (SMR) of YIG/Pt, but has a much larger anisotropy, of the order of 0.5%, which increases with the atomic number of the NM. This SMR-like behavior is absent in light NM/Co bilayers (NM = Ti, Cu), which present the standard AMR expected of polycrystalline FM layers. In the Ta, W, Pt/Co bilayers we find an additional magnetoresistance, directly proportional to the current and to the transverse component of the magnetization. This so-called unidirectional SMR, of the order of 0.005%, is largest in W and correlates with the amplitude of the antidamping spin-orbit torque. The unidirectional SMR is below the accuracy of our measurements in YIG/Pt.
@article{arxiv.1510.06285,
title = {Magnetoresistance of heavy and light metal/ferromagnet bilayers},
author = {Can Onur Avci and Kevin Garello and Johannes Mendil and Abhijit Ghosh and Nicolas Blasakis and Mihai Gabureac and Morgan Trassin and Manfred Fiebig and Pietro Gambardella},
journal= {arXiv preprint arXiv:1510.06285},
year = {2015}
}