Temperature dependence of spin pumping and inverse spin Hall effect in permalloy/Pt bilayers

The temperature dependence of the spin pumping process in Fe80Ni20 (Py)/Pt bilayers is analyzed for different Pt capping layer thickness. Samples have been grown by means of dc magnetron sputtering, at room temperature, on top of Si substrates. In order to get an optimized interface between the Py and the Pt layers, the Pt capping layers were deposited In situ. The values of the damping constant, alpha, obtained for the Py alone samples, around 0.007 at RT, make evident the good quality of the samples. The increase of alpha due to spin pumping into the Pt layer is clearly appreciated; alpha values in Py/Pt bilayers are twice the value in Py alone. Spin pumping is confirmed by direct measurements of the inverse spin Hall effect (ISHE) voltage signal (V-ISHE) measured across the samples. To separate ISHE and spin rectification contributions to V-ISHE the line shape analysis method has been used and the conditions for its applicability thoroughly discussed. V-ISHE increases almost linearly on lowering temperature for all the frequencies investigated and smoothly increases as frequency decreases showing roughly a linear dependence with the inverse of the frequency. The Pt layer thickness dependence of alpha and V-ISHE suggest a low interfacial spin mixing conductance and high spin memory loss.