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

摘要

We have measured the spin torques of beta-Tantalum / Co20Fe60B20 bilayersversus Ta thickness at room temperature using an FMR technique. The spin Hallcoefficient was calculated both from the observed change in damping coefficientof the ferromagnet with Ta thickness, and from the ratio of the symmetric andanti-symmetric components of the FMR signal. Results from these two methodsyielded 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-planespin torque originating from Ta, which is constant with Ta thickness. Weascribe this to an interface spin orbit coupling, or Rashba effect, due to thestrength and constancy of the torque with Ta thickness. From fitting measureddata to a model including interface spin orbit coupling, we have determined thespin diffusion length for beta-Tantalum to be ~2.5 nm.