Investigation of off-aligned exchange coupling by torque curve and ferromagnetic resonance

Abstract

Off-aligned exchange coupling in bilayer thin film is investigated by torque curve and ferromagnetic resonance (FMR). In off-aligned exchange coupling, the unidirectional anisotropy axis makes an angle β with the anisotropy axis of the ferromagnetic layer. The torque curves of the off-aligned exchange are shifted with respect to the ones of the aligned case (β=0). From the experimental measure of the shift angle α0 and of the torque curve slope at α0, one can determine independently the exchange anisotropy field HE and β values. A description of the FMR modes in such an off-aligned exchange coupling is given. The FMR mode position and linewidth are studied as a function of the anisotropy fields, of the off-aligned angle values, and of the applied field direction. The resonance frequency and frequency linewidth present particular features which will help to do the right interpretation of FMR spectra of these systems.