Effect of Single and Double Sintering on Microstructure and Magnetic Properties of Gd-Substituted Ni-Cd Ferrites

Two different groups, I and II, which are fired one and two times, respectively, from Ni-Cd ferrites of chemical formula Ni_0.7Cd_0.3Gd _x Fe_2?x O₄ (x = 0 to x = 0.1 with step = 0.025) have been prepared by conventional ceramic method. The effect of Gd-substitution on the microstructure and magnetic properties of the two groups has been studied. X-ray patterns indicated the presence of a minor secondary phase with the spinel phase at Gd-concentrations with x = 0.075 and 0.1. SEM and VSM are used to investigate the microstructure and to measure the magnetization of the samples at room temperature, respectively. The initial permeability is measured as a function of temperature and Curie temperature is determined. It was found that there are considerable differences in the microstructure and the magnetic properties of the two groups. Although the Gd-substitution decreased the values of both saturation magnetization M _s and initial permeability μ_i, the value of Curie temperature T _C has been improved. Moreover, the double sintering process improved the magnetization and densification of samples.