Critical angles effect: Vanishing of cubic magnetocrystalline anisotropy in ferromagnetic resonance spectra

The shapes of ferromagnetic resonance (FMR) spectra of laser deposited epitaxial Y3Fe5O12 (YIG) films strongly depend on the orientation of the magnetic field with respect to the crystalline axes of the film. Strain and compositional inhomogeneties in the films define local magnetic anisotropies and could be responsible for the complexity of FMR spectra. We show that, in accordance with the Smit-Suhl formula, the contribution from a spatial distribution of the cubic magnetocrystalline anisotropy to the FMR spectra vanishes at certain orientations ("critical angles") of the magnetic field. We prove experimentally that it is a necessary condition to orient the magnetic field at the critical angles in order to measure single-line FMR spectra in an inhomogenous laser deposited YIG film.