Parallel pump spin wave instability in thin ferromagnetic films

The spin wave instability generated by parallel pumping in a tangentially magnetized ferromagnetic film is considered, with simultaneous regard for both the dipole and exchange fields. A dispersion equation and some expressions for the critical microwave threshold of the spin wave parametric excitation have been obtained. The dependence of the critical field on the magnetizing field has an unusually oscillating character. This is connected both with the discreteness of spin wave spectrum and the peculiarities of spin wave polarization in a tangentially magnetized film.