The hot topic that dominated the recent InterMag conference, spin-Hall magnetoresistance (SMR) is the topic of this week’s pick, “Physical origins of new magnetoresistance in Pt/YIG” by Miao et al in PRL. To wade in on the debate as to the origins of the MR signal in the Pt/YIG system (SMR or proximity effect), several different samples of various thicknesses were prepared. Standard Pt/YIG acts as a reference, Pt grown on Ar bombarded YIG – bombarding the YIG surface produces a metallic Fe surface state on the YIG that greatly reduces the spin-mixing conductance of Pt/YIG but still allows for induced moments in the Pt, Pt grown on SiO2 (Fe 7%) where the SiO2 (Fe 7%) is a non-magnetic insulator but allows moments to be induced in Pt, and Pt/Au/YIG where the Au prevents an induced moment in the Pt but allows spin-mixing conductance. The spin/magnetic properties of the layers were characterised by SSE measurments.
The general conclusion of the paper, obtained by magneto-transport measurements of the various samples, is that both the SMR and proximity effect give rise to the Pt/YIG magnetoreistance effect, and both have the same symmetry (Rxx for magnetization out of plane is around the same as Rxx for magnetization in-plane parallel to current, which is greater than Rxx for magnetization in-plane perpendicular to current). At low fields the SMR effect, which should be constant with external field when magnetization of the YIG saturates, dominates, but as field increases the so does the proximity effect, so at high fields the proximity effect dominates.
The debate rages on
While these results seem persuasive (and got published in PRL), I am confident that the debate of the origin of the Pt/YIG MR effect will rage on for a while to come