Temperature dependence of spin pumping and Gilbert damping in thin Co/Pt bilayers

We report on the temperature dependence of the spin-pumping effect and the Gilbert damping in Co/Pt bilayers grown on Silicon oxide by measuring the change of the linewidth in a ferromagnetic resonance (FMR) experiment. By varying the Co thickness d(Co) between 1.5 nm and 50 nm we find that the damping increases inversely proportional to d(Co) at all temperatures between 300 K and 5 K, showing that the spin pumping effect does not depend on temperature. We also find that the linewidth increases with decreasing temperature for all thicknesses down to about 30 K, before leveling off to a constant, or even decreasing again. This behavior is similar to what is found in bulk ferromagnets, leading to the conclusion that in thin films a conductivity-like damping mechanism is present similar to what is known in crystals.