Temperature dependence of bulk and interface contributions to the magnetic damping of Permalloy thin films

The magnetic damping of Ni 80 Fe 20 [Permalloy (Py)] thin films is studied via temperature- and frequency-dependent ferromagnetic resonance (FMR) as a function of the Py layer thickness for two different thickness series, Al/Py/sapphire and Al/Py/Al/sapphire, respectively. Additional magnetic and structural characterization is done by superconducting quantum interference device magnetometry as well as x-ray reflectivity and transmission electron microscopy. The frequency dependence of the FMR linewidth allows us to separate the Gilbert-like contributions from non-Gilbert-like ones like two-magnon scattering (TMS) processes. The thickness dependence allows us to separate the derived magnetic parameters such as saturation magnetization M s , TMS contribution Γ , and Gilbert damping parameter α into their respective bulk and interfacial contributions. While the bulk contribution α bulk monotonously decreases with temperature from 0.0061(1) down to 0.0054(1) for both samples series, the interfacial contribution α interface shows a subsequent increase at low temperature. This is rather pronounced for the Al/Py/sapphire series, caused by a temperature-dependent TMS contribution. For the Al/Py/Al/sapphire series, the increase at low temperatures is much less pronounced, and a temperature-independent TMS contribution is only found for the thinnest sample due to a wavy Py film morphology. Correcting for the TMS contributions allows us to extract α bulk ( T ) which reflects the intrinsic magnetic damping properties of sputtered Py thin films.