Magnetization and permeability of polycrystalline ferrites with general formula Cd x Mg 1− x Fe 2− y Cr y O 4 ( x=0, 0.2, 0.4, 0.6, 0.8, 1.0; y=0, 0.05 and 0.10) were studied. Study of saturation magnetization reveals that the Neel's two-sublattice model exists upto x=0.4, for y=0, 0.05 and 0.1 and a three-sublattice model ( YK-model) is predominant for x>0.4 and y=0, 0.05 and 0.10. The saturation magnetization and magnetic moment were found to decrease with the increase in Cr 3+ contents, which is attributed to the dilution of B–B site interaction. Variation of initial permeability with temperature revealed the long-range ferromagnetic ordering in the compounds with x=0.4. The sample with x⩽0.4 and y=0, 0.05 and 0.10 showed peaking behavior near Curie temperature, which is attributed to the decrease of anisotropy constant K 1 to zero. Low-frequency dispersion of initial permeability suggests domain wall displacement. Addition of Cd 2+ resulted in a sharp decrease in Curie temperature. With the addition of Cr 3+, initial permeability was found to decrease.