Nonlinear phenomena and relaxation oscillations associated with magnetoelastic propagation in yttrium--iron garnet

S and X band room-temperature experiments are reported on the nonlinear behaviour of magnetoelastic waves in axially magnetised nonellipsoidal geometries of yttrium--iron garnet, when the specimens are mounted in resonant cavities. It is concluded that a finite power region exists for the observation of coherent oscillations or a noise-type spectrum.