Spin-Wave Resonance of Irradiated Permalloy Films

Abstract

A study of the spin-wave resonance in the parallel and perpendicular orientations at 9.5 GHz has been made on a number of irradiated Permalloy films (thicknesses: 900 to 3100 Å; melt composition: 80% Ni–20% Fe). The films were evaporated onto fused-quartz and soft-glass substrates in a vacuum initially at 2×10−8 Torr, annealed in a magnetic field for 12 h at 250°C (the substrate temperature during evaporation), and irradiated with 3×1017 He3 particles per cm2. The resonance patterns of the films show a number of interesting features, including changes in the resonance fields, Hn, and intensities, In. In the perpendicular orientation, Hn generally decreased with irradiation except for the two thicker films where Hn=1,2 increased; in the parallel orientation, Hn generally increased. In the perpendicular orientation, the intensity changes of the modes varied both with the order number and with the film thickness. In general, as a function of order number and excluding the first mode, In odd initially decreased for the thicker films, In even initially increased, and then all In increased; for the thinner films, all In initially increased and then decreased for n>4 or 5. In the parallel orientation, the intensity changes were generally less than in the perpendicular case. Annealing the films at 200°C shows that some of the irradiation-induced changes are reversible. The observed changes occur as a result of changes in a number of parameters: the stress in the film (including stress changes both in the film alone and in the substrate), the magnitude and the inhomogeneity of the magnetization, and the surface anisotropy (and hence spin pinning).