Hysteretic behavior of the dynamic permeability on a Ni-Fe thin film

The dynamic properties of a 30-nm-thick permalloy film have been investigated through permeability measurements in the 100-MHz to 3-GHz range, in the presence of an external field applied along the easy axis. The permeability depends not only on the applied field, but also on the orientation of the field compared to the remnant magnetization of the sample. The application of an external field antiparallel to the magnetization may decrease the resonance frequency compared to the zero-field permeability. Ferromagnetic resonance equations provide a good description of the dynamic bistability at low fields, but do not account for the observed behavior in the whole bistability range. This is attributed to the occurrence of a nonuniform resonance.