Experimental Demonstration of the Co-existence of the Spin Hall and Rashba Effects in beta-Tantalum/Ferromagnet Bilayers

TL;DR

This study experimentally demonstrates the coexistence of spin Hall and Rashba effects in beta-Tantalum/ferromagnet bilayers, quantifying spin torques and identifying interface spin orbit coupling at room temperature.

Contribution

It provides the first experimental evidence of simultaneous spin Hall and Rashba effects in beta-Tantalum/ferromagnet bilayers, with quantitative analysis of spin torques and interface effects.

Findings

Spin Hall coefficient of approximately -0.09 to -0.11.

Identification of a constant out-of-plane spin torque from Ta.

Estimated spin diffusion length of beta-Tantalum around 2.5 nm.

Abstract

We have measured the spin torques of beta-Tantalum / Co20Fe60B20 bilayers versus Ta thickness at room temperature using an FMR technique. The spin Hall coefficient was calculated both from the observed change in damping coefficient of the ferromagnet with Ta thickness, and from the ratio of the symmetric and anti-symmetric components of the FMR signal. Results from these two methods yielded values for the spin Hall coefficient of -0.090+/-0.005 and -0.11+/-0.01, respectively. We have also identified a significant out-of-plane spin torque originating from Ta, which is constant with Ta thickness. We ascribe this to an interface spin orbit coupling, or Rashba effect, due to the strength and constancy of the torque with Ta thickness. From fitting measured data to a model including interface spin orbit coupling, we have determined the spin diffusion length for beta-Tantalum to be ~2.5 nm.