Study of Frequency Dispersion of Permeability in PVDF/Ni_0.4Zn_0.6Fe₂O₄ Composites and Its Influence on Microwave Absorption Characteristics

Often, when describing the electromagnetic properties of polymer composites in the microwave range, little attention is paid to magnetic spectra and the description of their features using known dispersion models. In this paper, we investigate the microstructure and frequency spectra of the complex permittivity and complex permeability of the ferrite-polymer composite PVDF/Ni_0.4Zn_0.6Fe₂O₄ in the frequency range of 100 MHz–5 GHz and a mass concentration of 10–80 wt.%. The composite structure was investigated by scanning electron microscopy, while the frequency dependences of permittivity and magnetic permeability were measured using a vector network analyzer together with the Nicholson–Ross–Weir method. In the course of the work, using the fitting of the experimental spectra by known models of natural ferromagnetic resonance and domain wall resonance, the features of the dispersion of the magnetic spectra were explained. In particular, the shift of resonance frequency and the dominant contribution of spin rotation to the permeability value were interpreted using the results of fitting. In addition, comparison of the features of the reflection loss spectra and the results of model fitting helped to identify the main contribution of the spin rotation process to the attenuation of the electromagnetic wave in composites. The results obtained in the work are relevant for the development of new approaches to predicting the electromagnetic characteristics of composites using effective medium models.