Spin Hall Angle and Spin Diffusion Length in Au–Cu Alloy

Abstract

We experimentally measured the fieldlike spin–orbit torque (SOT) by the second-order planar Hall effect, as well as the dampinglike SOT by the polar magnetooptic Kerr effect in NiFe(1.5 nm)/AuCu( $x$ nm) bilayers with $2~\textrm {nm} \le x \le 8$ nm. We found that the spin diffusion length in the Au–Cu alloy is $\sim 5$ nm, which is shorter than that of pure Au and Cu. When the thickness of the AuCu layer is above the spin diffusion length, the spin Hall angle of the Au–Cu alloy is $\sim 1.3\pm 0.2$ %, which is much larger than that of pure Cu and Au. The results imply that large spin Hall angle materials can be explored in the nonmagnetic alloys of constituent elements having weak or negligible spin–orbit coupling.