Brillouin light scattering spectroscopy of parametrically excited dipole-exchange magnons

摘要

The spectral distribution of parametrically excited dipole-exchange magnonsin an in-plane magnetized epitaxial film of yttrium-iron garnet was studied bymeans of frequency- and wavevector-resolved Brillouin light scatteringspectroscopy. The experiment was performed in a parallel pumping geometry wherean exciting microwave magnetic field was parallel to the magnetizing field. Itwas found that for both dipolar and exchange spectral areas parallel pumpingexcites the lowest volume magnon modes propagating in the film planeperpendicularly to the magnetization direction. In order to interpret theexperimental observations, we used a microscopic Heisenberg model that includesexchange as well as dipole-dipole interactions to calculate the magnon spectrumand construct the eigenstates. As proven in our calculations, the observedmagnons are characterized by having the highest possible ellipticity ofprecession which suggests the lowest threshold of parametric generation.Applying different pumping powers we observe modifications in the magnonspectrum that are described theoretically by a softening of the spin stiffness.