Ni1−xCoxFe1.98O4 Ferrite Ceramics with Promising Magneto‐Dielectric Properties

Abstract

The dielectric and magnetic properties of Ni1−xCoxFe1.98O4 (with x=0.005, 0.01, 0.02, and 0.05) ferrite ceramics, doped with 5% Bi2O3 as a sintering aid, were investigated. X‐ray diffraction results indicated that there is no obvious reaction between Bi2O3 and the ferrites within the temperature range. All samples were fully densified after sintering at temperatures of ≥1000°C for 2 h. Densification behavior, microstructural development, and grain growth of the Ni1−xCoxFe1.98O4 ferrite ceramics are independent of the concentration of Co. The appropriate sintering temperature range for achieving a low dielectric loss tangent is 1000°–1050°C. The high dielectric loss tangent of the samples sintered at temperatures of <1000°C is due mainly to the conduction losses caused by their porous microstructures, while that of the samples sintered at temperatures of >1050°C is not readily explainable at the moment. The variation in the magnetic properties (static permeability) can be understood in terms of the magnetocrystalline anisotropic constant combined with the single‐ion model. Promising magneto‐dielectric properties have been obtained in Ni0.99Co0.01Fe1.98O4 and Ni0.98Co0.02Fe1.98O4, both sintered at 1050°C for 2 h, over 3–30 (high frequency) and 30–90 MHz, respectively. Such materials might find potential applications such as in antenna miniaturizations.