The four-magnon instability of magnetostatic surface waves (MSSWs) in
yttrium iron garnet epitaxial films is investigated experimentally. It
is shown that four-magnon instability fur MSSWs with wave numbers 30-
600 cm(-1) is a decay instability and develops for values of the wave
magnetization close to the threshold level for second-order parametric
instability of a homogeneous transverse pump wave. When the supercrit
icality of the MSSW power is 15-20 dB, the generated parametric spin w
aves themselves become unstable with respect to the four-magnon intera
ction, so that kinetic instability develops in the film. It is shown t
hat the pump signal transmitted through the signal and the length of t
he ''nonlinear'' part of the film, where a MSSW is capable of exciting
parametric spin waves, increase as the pump power is increased. (C) 1
997 American Institute of Physics.