  We measure and analyze the effective spin Hall angle of platinum in the low
residual resistivity regime by second harmonic measurements of the spin-orbit
torques for a multilayer of Pt/Co/AlO$_x$. An angular dependent study of the
torques allows us to extract the effective spin Hall angle responsible for the
damping-like torque in the system. We observe a strikingly non-monotonic and
reproducible temperature dependence of the torques. This behavior is compatible
with recent theoretical predictions which include both intrinsic and extrinsic
(impurities and phonons) contributions to the spin Hall effect at finite
temperature.
