Crystallographic and d.c. electrical resistivity study of Cd-Co and Cr³⁺ substituted Cd-Co ferrites

Abstract

Polycrystalline compounds of the series Cd_xCo_1-xFe_2-yCr_yO₄ (x = 0, 0.25, 0.50, 0.75 and 1.00; y = 0, 0.15 and 0.30) were prepared by a standard ceramic technique. The crystallographic data were obtained using X-ray diffraction. All the compounds were found to have f.c.c. symmetry. The ionic radii on A and B sites (r_A and r_B, respectively) and the bond lengths on A and B sites (A–O and B–O, respectively) were calculated. The values of r_B and B–O were found to be greater than r_A and A–O, except for the Cd and Cr³⁺ substituted Cd ferrites. The d.c. electrical resistivity of pelletized samples was calculated by measurements of voltage and current using a two-probe method at various temperatures. The values of Curie temperatures (T_c) observed in d.c. resistivity measurements, for all the composition under investigation, were found to be in good agreement with those observed in susceptibility measurements and by the Loria–Sinha technique. The activation energies (Δ E) were found to be higher in the para-region than in the ferri-region. The resistivity of the samples is found to be dependent on the saturation magnetic moments (nβ) of the samples. The resistivity of Co ferrite is found to be higher than that of Cd ferrite at 475 K.