SPIN-WAVE SELF-OSCILLATIONS - EXPERIMENTAL-VERIFICATION OF THE 2-MODE ORIGIN (INVITED)

Most theoretical models used to explain self-oscillations and chaotic phenomena observed in microwave pumped spin-wave instabilities are based on the assumption that the dynamics is governed by a few interacting modes. This assumption is somewhat disturbing because it is known that in principle an extremely large number of modes can be excited when the microwave field h exceeds the Suh1 instability threshold h(c). In this paper we describe pulsed microwave (8.2 GHz) spin-wave pumping experiments in spheres and films of yttrium-iron-garnet which clearly demonstrate that, with increasing power, one mode is excited at h=h(c), a second mode appears at h > h(c), and subsequently the self-oscillation sets in. The observations agree very well with computer results for the transient behavior of the spin-wave equations, showing that the two-mode assumption for the onset of self-oscillation is correct. We also present data for films which add evidence to the sample-size dependence of the self-oscillation frequency and support recent improvements proposed for the two-mode model.