Ferrimagnetic resonance lineshape asymmetry due to Suhl instabilities

Abstract

We present calculations of the ferrimagnetic resonance lineshapes resulting from second order Suhl instabilities for thin films and spheres. We find that whereas a spherical sample has a lineshape which is symmetrical around the resonant frequency, a thin film has an asymmetrical lineshape. The calculations are in agreement with measurements that we have performed of the lineshape as a function of input power for thin film samples of both barium ferrite and yttrium iron garnet. When the magnetic field direction is changed from perpendicular to parallel to the film plane, the asymmetry of the lineshape at magnetic resonance changes in opposite sense relative to the resonant field. Theoretical estimates of the critical microwave field necessary for second order Suhl instabilities to occur are in agreement with measured critical fields.