The nonlinear instability threshold of acoustic modes efficiently coupled with dipole magnetostatic wave (MSW) has been investigated experimentally. MSW were excited in the range of magnetic fields and frequencies where spin-wave resonances have the same wavelength as transversal acoustic modes wavelength. Planar structures with yttrium-iron garnet films were used in experiments at frequencies in 3-6 GHz range. The strong reconstruction of bulk acoustic and spin wave spectra is observed in the range of frequencies and magnetic fields near exchange MSW and transversal AW dispersion curve crossover region. The reason is the strong modification of magnetoacoustic mode structures : eigen frequencies and eigen functions describing the distribution of RF magnetization and elastic displacements over the thickness of the planar structure. As a result the excitation of exchange-acoustic waves have been observed in a rather wide range of spectra (up to 50 MHz) in the vicinity of MSW and AW dispersion curve crossover region. Non-linear characteristics of the acoustomagnetic mode spectrum has been investigated.
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