Particle Size and Concentration Effect on Permeability and EM-Wave Absorption Properties of Hybrid Ferrite Polymer Composites

Hybrid MnZn/NiZn/PVC polymer composite materials have been prepared using a dry low-temperature hot-pressing process and the influence of particle size, concentration, and the fraction ratio of the dual MnZn/NiZn ferrite filler on their complex permeability $\mu = \mu^{\prime}-{\rm j}\ \mu^{\prime\prime}$ and electromagnetic wave (EM-wave) absorbing properties were investigated within the frequency range of 1–3000 MHz. The observed frequency dispersion of permeability was of a relaxation type and caused by a resonance of vibrating domain walls and a natural ferromagnetic resonance of precessing magnetic moments in domains. The complex permeability and resonance frequency $f_{\rm res}$ of hybrid composites have been affected mainly by changes in concentration and fraction ratio of ferrite filler: the $\mu^{\prime}$ at low frequency decreased and $f_{\rm res}$ shifted towards the higher frequency region with the decrease of ferrite concentration and with the configuration change from the MnZn/PVC composite to NiZn/PVC one. Measured values of complex permeability were used to determine the return loss RL using a model of a single-layered EM-wave absorber backed by a perfect conductor. In the designed single layer absorbers, the RL as well as the matching frequency $f_{\rm m}$, matching thickness $d_{\rm m}$, bandwidth $\Delta f$ for ${\rm RL} \leq -20$ dB, and the minimum of return loss $({\rm RL})_{\min}$ seem to be strongly dependent on particle size, concentration, and the fraction ratio of the dual MnZn/NiZn ferrite filler.