Effect of Bi-Co co-doping on the microstructure and magnetic properties of NiMgCuZn ferrites

Ni0.15−xMg0.1Cu0.3Zn0.45BixCoxFe2−xO4 (x = 0, 0.01, 0.02, 0.03) ferrites were prepared by sol-gel auto-combustion method. The X-ray diffraction confirmed the formation of the single-phase spinel structure when x ≤ 0.02. The microstructures were examined by SEM. The liquid phase produced by high temperature sintering promoted the grain growth and decreased the porosity. Magnetic measurements showed that saturation magnetization decreased continuously with the substitution of Bi and Co contents, whereas, the initial permeability increased with increase in Bi-Co content up to 0.02 followed by a decrease. In addition, Incorporation of Bi-Co resulted in the increase in quality factor and the decrease in loss factor, which implies that NiMgCuZn ferrite doped with Bi-Co is suitable for high frequency applications. Moreover, the Ni0.13Mg0.1Cu0.3Zn0.45Bi0.02Co0.02Fe1.98O4 sample exhibited the largest density, the highest initial permeability, and the lowest loss.