Evidence of Unpinned Surface Spins from Parallel Spin-Wave Resonances in Permalloy Films

Abstract

The nature of the surface‐spin boundary condition and of the parallel resonances (H ∥ film) for spin‐wave resonance in Permalloy films is determined. Computer solutions of the classical equation of motion of the spins, using the inhomogeneous internal field model, are compared with experimental results. The mode positions and intensities as a function of frequency, film thickness, and internal effective field variation are calculated. This results in the conclusion that the surface spins are unpinned and that the inhomogeneous internal field model is valid for the parallel case as well as for the perpendicular (H ⊥ film) case. The frequency dependence of the intensity of the parallel modes is particularly strong evidence for this conclusion. It is also shown that the mode positions for the prependicular case are unlikely to reliably determine the surface‐spin boundary condition.