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 ₏ₓ is strongly dependent on thickness t₏ₓ. The dampinglike spin Hall torque efficiency per unit current density ₃₋^j varies significantly with t₏ₓ, exhibiting a peak value ₃₋^j=0. 12 at t₏ₓ=2. 8--3. 9 nm. In contrast, ₃₋^j/₏ₓ increases monotonically with t₏ₓ and saturates for t₏ₓ>5 nm, consistent with an intrinsic spin Hall effect mechanism, in which ₃₋^j is enhanced by an increase in ₏ₓ. Assuming the Elliott-Yafet spin scattering mechanism dominates, we estimate that the spin diffusion length ₒ= (0. 770. 08) 10^-15 m^2/₏ₓ.