Ferromagnetic resonance linewidth in metallic thin films: Comparison of measurement methods

TLDR

The study measured Permalloy film FMR linewidths using stripline, VNA, and PIMM techniques at fixed frequencies (1.5–5.5 GHz) and fields (1.6–8 kA m⁻¹). All three techniques yielded consistent linewidths, with a linear frequency dependence giving a damping parameter α = 0.007 and low‑frequency intercepts of 160–320 A m⁻¹, while the frequency‑domain data show slight curvature at low frequencies and saturation at high frequencies.

Abstract

Stripline (SL), vector network analyzer (VNA), and pulsed inductive microwave magnetometer (PIMM) techniques were used to measure the ferromagnetic resonance (FMR) linewidth for a series of Permalloy films with thicknesses of 50 and 100nm. The SL-FMR measurements were made for fixed frequencies from 1.5to5.5GHz. The VNA-FMR and PIMM measurements were made for fixed in-plane fields from 1.6to8kA∕m (20–100Oe). The results provide a confirmation, lacking until now, that the linewidths measured by these three methods are consistent and compatible. In the field format, the linewidths are a linear function of frequency, with a slope that corresponds to a nominal Landau-Lifshitz phenomenological damping parameter α value of 0.007 and zero frequency intercepts in the 160–320A∕m (2–4Oe) range. In the frequency format, the corresponding linewidth versus frequency response shows a weak upward curvature at the lowest measurement frequencies and a leveling off at high frequencies.