EXCHANGE SPIN-WAVES IN NONUNIFORM YTTRIUM-IRON-GARNET FILMS

Spin wave resonance spectra have been observed in yttrium iron garnet films. The spectra exhibit as many as 120 strongly excited modes with large deviation from quadratic spacing, which are interpreted in terms of a thickness variation of the effective magnetization 4 pi M(x) dep ending both on the magnetization and the anisotropy field. Profiles of 4 pi M(x) are calculated from the spectra measured both in parallel a nd in perpendicular bias magnetic fields. It has been shown that the f ilms tested have monotonic variations of the effective magnetization. The difference 4 pi Delta M between upper and lower 4 pi M(x) values i s as large as 330 G. It is shown that exchange-dominated spin waves (E SW) with the maximum wave number of 2.5X10(5) cm(-1) have been excited under experiment conditions. Microwave pulse delay due to ESW propaga tion across the film thickness has been observed. Delay versus frequen cy characteristics strongly depend on the profile M(x) and the directi on of the applied magnetic field. Profiles M(x) have been calculated t o provide both constant and linear delay-versus-frequency characterist ics.