Spin torque study of the spin Hall conductivity and spin diffusion length in platinum thin films with varying resistivity

Abstract

We report measurements of the spin torque efficiencies in perpendicularly-magnetized Pt/Co bilayers where the Pt resistivity \(\rho_{Pt}\) is strongly dependent on thickness \(t_{Pt}\) . The damping-like spin Hall torque efficiency per unit current density, \(\xi^j_{DL}\) , varies significantly with \(t_{Pt}\), exhibiting a peak value \(\xi^j_{DL}=0.12\) at \(t_{Pt} = 2.8 - 3.9\) nm. In contrast, \(\xi^j_{DL}/\rho_{Pt}\) increases monotonically with \(t_{Pt}\) and saturates for \(t_{Pt} > 5\) nm, consistent with an intrinsic spin Hall effect mechanism, in which \(\xi^j_{DL}\) is enhanced by an increase in \(\rho_{Pt}\) . Assuming the Elliott-Yafet spin scattering mechanism dominates we estimate that the spin diffusion length \(\lambda_s = (0.77 \pm 0.08) \times 10^{-15} \Omega m^2 /\rho_{Pt}\).