Influence of oxidic and metallic interfaces on the magnetic damping of Permalloy thin films

Magnetic damping within ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ (Permalloy, Py) thin films is studied via temperature- and frequency-dependent ferromagnetic resonance (FMR) experiments. While the Py thickness is kept constant at 20 nm, the environment at the film interfaces was systematically varied by fabricating a set of Py thin films grown on widely used substrates and capped with common layers, which are assumed to be suitable to prevent oxidation. The resulting frequency and temperature dependence of the FMR linewidth significantly deviates from the expected Gilbert-like behavior and especially for oxidic interfaces unwanted non-Gilbert-like contributions to the magnetic damping appear, in particular, at low temperatures. In contrast, metallic capping layers avoid non-Gilbert-like contributions. In particular, Py sandwiched in between Al metallic capping and buffer layers exhibits negligible inhomogeneous FMR linewidth broadening and a very small, purely Gilbert-like contribution of $\ensuremath{\alpha}=0.0066(2)$ down to the lowest temperature.