Three- and four-magnon decay of nonlinear surface magnetostatic waves in thin ferromagnetic films

The propagation of nonlinear monochromatic surface magnetostatic waves in thin ferromagnetic films is investigated. It is shown that these waves are unstable above a certain threshold intensity causing satellite waves to be excited through magnon decay processes. It is shown that the small value of the threshold intensity is consistent with first-order (three-magnon) effects. In the regime where these effects are forbidden, another higher threshold intensity exists that is due to second-order (four-magnon) effects. Analytical forms for the threshold intensities, together with numerical estimates, are also presented.