Nonlinear domain-mode ferromagnetic resonances in garnet films with perpendicular anisotropy

The zero-field domain-mode ferromagnetic resonances (DM-FMRs) in the weakly nonlinear regime have been investigated for garnet films with a perpendicular anisotropy supporting parallel stripe domains by means of broadband microwave measurements, and analytical and numerical approaches. First, the perpendicular ferromagnetic resonance (FMR) in the saturated state is considered as a reference case. A redshift of the resonance frequency and a broadening of the resonance line are experimentally observed for increasing the input microwave power. These power-dependent characteristics are nicely reproduced by an analytical model taking into account the linear polarization of the pumping field and a nonlinear Gilbert-type damping parameter. Then, the effect of the stripe domain pattern is analyzed. A redshift and a line broadening are also experimentally revealed both for the acoustic and the optical modes with an anisotropic character between the two modes. Numerical simulations based on the DM-FMR model extended in the nonlinear regime and including a nonlinear Gilbert-type damping parameter account quantitatively for the power dependences of the DM resonance frequency shifts and the DM resonance linewidths. These results highlight the requirement of a nonlinear damping term for explaining the FMR and DM-FMR spectra in the weakly nonlinear regime within the framework of the phenomenological approach of magnetization dynamics.