Spin Torque Study of the Spin Hall Conductivity and Spin Diffusion Length in Platinum Thin Films with Varying Resistivity

We report measurements of the spin torque efficiencies in perpendicularly magnetized Pt/Co bilayers where the Pt resistivity ρPt is strongly dependent on thickness tPt. The dampinglike spin Hall torque efficiency per unit current density ξDLʲ varies significantly with tPt, exhibiting a peak value ξDLʲ=0.12 at tPt=2.8--3.9 nm. In contrast, ξDLʲ/ρPt increases monotonically with tPt and saturates for tPt>5 nm, consistent with an intrinsic spin Hall effect mechanism, in which ξDLʲ is enhanced by an increase in ρPt. Assuming the Elliott-Yafet spin scattering mechanism dominates, we estimate that the spin diffusion length ${{λ}}ₛ=(0.77±{}0.08)×{}{10}^{{-}15} {{Ω}}·{}{m}²/{{ρ}}Pt$.