Extrinsic contribution to Gilbert damping in sputtered NiFe films by ferromagnetic resonance

We quantitatively determine the intrinsic and extrinsic contribution to frequency (Δfres) and field (ΔH) linewidths using Network Analyzer ferromagnetic resonance (NA-FMR) (using two different excitation cells) and conventional ferromagnetic resonance (FMR) techniques in sputtered thin permalloy (NiFe) films. There are some common features in these two FMR measurements, which allow us to get important information on damping mechanisms and structural magnetic qualities. The NA-FMR data show an increase in frequency linewidth (Δfres) as magnetic field (H) increases. A distinct change in the slope of this increase is noted for a field above 200 Oe. To explain this result, we consider available theories including the “two-magnon” model, and the “local-resonance” model. From a fitting of Δfres versus H data to the Arias-Mills' two-magnon model results, we obtain the Gilbert damping parameters. The frequency variation of conventional FMR linewidth (ΔH) data also yields an effective value for the Gilbert damping (αeff=0.0128), in good agreement with the data from the Network Analyzer data (0.013±0.004). In addition to the theoretical analysis presented in this paper, we compare our experimental results from RF-excitation cell to the commonly used co-planer waveguide technique.