Dielectric and Magnetic Properties of Two-Phase Composite System: Mn-Zn or Ni-Zn ferrites in Dielectric Matrices

Abstract

The development of novel electromagnetic materials for various applications largely depends on ferrite composites with optimal combination of constituent elements. The evaluation of their dielectric and magnetic properties is important in understanding the physical properties and potential for specific use. In this work, permittivity and permeability spectra of composite materials based on granulated soft magnetic Mn-Zn and Ni-Zn ferrites in paraffin, polyvinyl acetate glue and silicone sealant matrices were investigated for different ferrite phase concentrations and ferrite granule sizes. Mn-Zn ferrites are characterized by a relatively large conductivity and their composites show unusual behavior for the real part of the permittivity which can be essentially higher than the values observed for bulk ferrite samples, especially at low frequencies. The permittivity spectra also demonstrate a strong frequency dispersion which is not seen for bulk ceramic ferrites. Ni-Zn ferrite composites with very large electrical resistance do not show these effects and their microwave properties are consistent with the behavior of the constituent phases. The observed permittivity enhancement is explained on the basis of the conductive properties of the ferrite granules and the equivalent capacitance effect. The effective permittivity calculated from an equivalent capacitor circuit gives a qualitative agreement with the experimental data at lower frequencies. However, the origin of the frequency dispersion remains unclear. The developed composites have a potential for applications in broadband absorbers since they combine magnetic and electric losses along with a strong frequency dispersion of the permittivity.