Ni1-xCoxFe1.98O4 ferrite ceramics with promising magneto-dielectric properties

Abstract

The dielectric and magnetic properties of Ni1-xCo xFe1.98O4 (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-xCoxFe 1.98O4 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 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 Ni0.99Co0.01Fe 1.98O4 and Ni0.98Co0.02Fe 1.98O4, 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. © 2008 The American Ceramic Society.