Standing Spin Wave Mode Spectra in Thin Permalloy Films Prepared in Vacuum of 10−7 Torr

Abstract

The spacings between the standing spin wave modes excited in Permalloy films, prepared in a high‐vacuum system at pressures near 10⁻⁷ Torr, are found to obey a quadratic dependence on order number for the magnetic field normal to the plane of the film (H_⊥) as well as in the plane of the film (H_II). The spacings and intensities of the modes, as a function of the angle φ which the magnetic field makes with respect to the film normal, indicate that the modes are nearly unpinned for φ_crit>φ≥90° (H_II), are completely unpinned at φ_crit, and partially pinned for φ_crit>φ≥0° (H_⊥). This type of pinning behavior is explained qualitatively by assuming that the films are nearly uniformly magnetized except for a very thin surface layer, of the order of ten lattice spacings, which exhibits a lower magnetization than the bulk. In addition, the observed pinning for the modes suggests that the boundary condition imposed on the transverse component of the magnetization at an air‐ferromagnetic interface is that the normal derivative of the magnetization vanish. It is concluded that ferromagnetic films prepared in high vacuum should be suitable for the determination of physical parameters, such as A/M, the ratio of exchange constant to the saturation magnetization, as their spectra are relatively free from the anomalous features observed in all of the previously reported SSWM investigations. Experimental evidence is presented that these anomalous features are probably due to contamination of the films by both residual gases in the evaporation chamber and by impurities introduced by the vacuum system itself.