Magneto‐Dielectric Properties of Mg–Cu–Co Ferrite Ceramics: II. Electrical, Dielectric, and Magnetic Properties

DC resistivity, dielectric, and magnetic properties of Mg-ferrite ceramics (Mg1−xCuxFe1.98O4, with x=0.10–0.30, and Mg0.90−xCoxCu0.10Fe1.98O4, with x=0.05–0.20) were investigated. A primary objective is to develop magneto-dielectric materials with almost equal values of permeability and permittivity, as well as low magnetic and dielectric loss tangent, for miniaturization of antennas. The MgFe1.98O4 ceramic sintered at 1125°C possessed values of permeability and permittivity of ∼6.5, and relatively low magnetic and dielectric loss tangents of <10−2, with a sintered density of only ∼70% of the theoretical density. Incorporation of Cu was found to be able to not only improve the densification and grain growth but also alter the electrical and magnetic properties of MgFe1.98O4. Further modification by Co resulted in promising magneto-dielectric materials, with an almost equal permeability and permittivity of ∼9.5 over 3–30 MHz (HF band). Together with their low magnetic and dielectric loss tangents and good sinterability, this class of magneto-dielectric materials could be potential candidates for the design of small antennas in the HF band (3–30 MHz). The DC resistivities and complex relative permittivities of the ferrite ceramics were discussed with respect to their microstructure, grain size, and the formation of Fe2+ ions. The variation of high-frequency magnetic properties of the ferrite materials with sintering temperature can be quantitatively understood by the magnetic circuit model and the Snoek-like law.