A MODEL FOR SPIN-WAVE AUTOOSCILLATIONS IN FINITE-SIZE MAGNETIC SAMPLES

A theory of collective oscillations in a system of spin waves parametr ically excited by homogeneous parallel pumping in a finite-size ferrom agnetic sample is developed. This theory is an extension of the well-k nown S theory of spin-wave collective oscillations in an infinite ferr omagnetic medium for the case when the boundary conditions in a magnet ic sample of finite size D are taken into account. We explain the foll owing experimentally observed proper-ties of spin-wave auto-oscillatio ns that were not explained by the existing models of this phenomenon. (i) The difference between the threshold of parametric excitation of s pin waves h(th) and the threshold of auto-oscillations h(osc). (ii) Th e finite value of the auto-oscillation frequency f(osc) at the thresho ld of auto-oscillations. (iii) The dependences of the threshold h(osc) and the frequency f(osc) of the spin-wave auto-oscillations on the si ze of the ferromagnetic sample. The results of the theory are in a goo d qualitative agreement with experimental results.