Thickness-dependent resonance frequency of non-uniform procession mode in CoZr stripe-domain magnetic films

The magnetic properties of CoZr magnetic thin films with stripe domains are investigated. The nanocrystalline grain size of 21.2 nm of CoZr thin film was obtained by x-ray diffraction spectra. The rotatable stripe-domain structure of the samples can be clearly observed from the magnetic force microscopy images. From the results of the M–H loop, the typical loops with domain structure of the samples can also be seen. The saturation magnetic fields of the thin films increase as a function of stripe half period in static magnetic properties. In dynamic magnetic properties, we find two precession modes, which include one traditional uniform precession mode with the resonance peak position in the low-frequency band and the other as the non-uniform precession mode with the resonance peak position in the high-frequency band. The ferromagnetic resonance frequencies of the non-uniform procession mode, which are driven by the exchange coupling between adjacent domains, show a decrease in behavior from 5.11to 3.52 GHz in the zero-field dynamic permeability spectra with the stripe domain's half period increasing, while the ferromagnetic resonance frequencies of the uniform procession mode nearly remain constant. Similar behavior of exchange coupling can be found by analyzing the field-dependent dynamic permeability spectra of CoZr films, which indicates that the main contribution of the thickness-dependent resonance frequency is the exchange coupling between neighboring stripe domains.