Damping at normal metal/permalloy interfaces

We have determined the Gilbert damping parameter as a function of layer thickness in six sets of samples with either a normal metal (NM)/Permalloy (NiFe) or NM/NiFe/NM structure by measuring the ferromagnetic resonance (FMR) linewidth for all series and correcting for extrinsic broadening effects. In the NM/NiFe samples, we find that increasing the interface roughness increases the damping quadratically from 0.01 at 3 nm to 0.11 at 47 nm, and by controlling the roughness of the copper layer, we have found there is no evidence of increased damping due to the thickness of the copper layer between 100-2050 nm of copper.