Non-magnetic origin of spin Hall magnetoresistance-like signals in Pt films and epitaxial NiO/Pt bilayers

Abstract

Electrical control of magnetic order in antiferromagnetic insulators (AFIs) using a Pt overlayer as a spin current source has been recently reported, but detecting and understanding the nature of current-induced switching in AFIs remain a challenge. Here, we examine the origin of spin Hall magnetoresistance-like signals measured in a standard Hall bar geometry, which have recently been taken as evidence of current-induced switching of the antiferromagnetic order in Pt/AFI bilayers. We show that transverse voltage signals consistent with both the partial switching and toggle switching of the Néel vector in epitaxial Pt/NiO bilayers on Al2O3 are also present in Pt/Al2O3 in which the AFI is absent. We show that these signals have a thermal origin and arise from (i) transient changes in the current distribution due to nonuniform Joule heating and (ii) irreversible changes due to electromigration at elevated current densities, accompanied by long-term creep. These results suggest that more sophisticated techniques that directly probe the magnetic order are required to reliably exclude transport artifacts and thus infer information about the antiferromagnetic order in such systems. Keywords: Magnetic ordering; Transition metal oxides; Magnetism; Spintronics; Hall effect; Epitaxy; Spin Hall effect; Scanning electron microscopy; Magnetron sputtering; Electromigration