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.