Large Angle Ferromagnetic Resonance

The steady state solutions of the Landau-Lifshitz-Gilbert (LLG) equation for single domain particles with uniaxial anisotropy and a circularly polarized AC field H_ac perpendicular to the anisotropy axis. The system has only two degrees of freedom, the angle between the magnetization and the anisotropy axis (which determines the "orbit" of the precession of the magnetization) and the phase shift between the magnetization and the AC field. The steady state solutions are characterized by a stable orbit (i.e. the damping towards the anisotropy field is compensated by the AC field) and the magnetization precessing at the frequency of the AC field. The model is extended for an external bias field parallel to the anisotropy axis. It will be shown that an external bias field essentially leads to a shift of the resonance frequency and the associated precession orbit.