Light-induced modification of the fmr spectra of a bismuth-substituted yttrium ferrite garnet film

A modification of the low-field ferromagnetic resonance (FMR) spectra of an easy-plane BiY$_2$Fe$_{4.4}$Sc$_{0.6}$O$_{12}$ film under irradiation with linearly polarized light with a wavelength of 680 nm at room temperature is experimentally detected. It is shown that the photoinduced change in the magnetic anisotropy is not related to thermal effects and it leads to a shift of the FMR frequency. A photoinduced decrease in the magnetoelastic coupling is indicated by a decrease in the depth of dips in the FMR spectra at frequencies corresponding to the resonance of transverse modes of elastic vibrations over the thickness of the epitaxial structure. The observed effects are due to a change in the populations of the energy levels of photoactive centers in the impurity magnet. It has been shown that the contribution to the photoinduced shift of the FMR frequency that depends on the direction of light polarization is an order of magnitude smaller than the main contribution that does not depend on the direction of polarization. The dependence of the FMR frequency on the direction of the electric field vector of the light wave is due to the nonlinear interaction of light and magnetization, which is described by the fourth-rank material tensor.