PARALLEL PUMPING FINE-STRUCTURE AT 9.4 GHZ FOR INPLANE MAGNETIZED YTTRIUM-IRON-GARNET THIN-FILMS

A fine structure in the parallel pumping spin wave instability absorpt ion has been observed. The data were obtained at 9.4 GHz on a narrow l inewidth in-plane magnetized yttrium iron garnet film with a magnetic layer thickness of 15.9 mu m. The standard butterfly curve of the spin wave instability threshold microwave field amplitude h(crit) versus e xternal static magnetic field H-ext was constructed from h(crit) deter minations obtained by sweeping the static field at different microwave power levels and measuring the change in microwave loss. For values o f H-ext below the minimum, h(crit) position, the loss versus H-ext pro files showed a characteristic-fine structure previously observed only in spheres. The fine structure spacing was on the order of 5 Oe and th e square of the spacing decreased linearly with increasing static fiel d. These fine structure results are in accord with predictions from th eory for critical modes at one-half the pump frequency, with the criti cal mode wave vectors aligned perpendicular to the film plane, and wit h the wave numbers for these modes quantized as standing spin wave mod es for a thin film. Analysis of the fine structure data gives a spin w ave exchange stiffness parameter D-fs=(6.0+/-0.9) X 10(-9) Oe cm(2) wh ich agrees within experimental error with the value D=(5.4+/-0.2) X 10 (-9) Oe cm(-2) obtained from Brillouin light scattering measurements o n YIG spheres. The standing wave critical modes are explained in terms of cooperative volume dipole-dipole and shape demagnetizing induced e llipticity for the modes.