Secondary peaks on microwave permeability spectra of soft ferromagnetic thin films with in-plane anisotropy

Complex permeability spectra of CoNbZr thin films have been measured up to 4GHz by a single coil pertubation technique. In addition to the well-known ferromagnetic resonance, multiple resonant modes have been evidenced in the increasing branches of the spectra. The number of “secondary peaks” observed depends on the sample thickness. Their resonance frequencies follow a nonlinear dispersion law versus the ratio of the mode number over the sample thickness with a power factor close to 1.5.