LAUSR

Abstract Nanoparticles of Cr substituted Co-Mg ferrites with chemical composition Co 0.5 Mg 0.5 Cr x Fe 2−x O 4 (0 ≤ x ≤ 1) have been synthesized by sol-gel auto combustion route. Rietveld refined powder X-ray diffraction patterns confirmed nanocrystalline single phase formation of all the ferrite samples in the face centred cubic spinel structure in the space group of Fd 3 m (No. 192). Cr doping for Fe in the Co-Mg ferrite leads to monotonic decrease in the saturation magnetization at 300 K as well as at 5 K, which can be described due to the weakening of super exchange interaction because of the replacement of Fe 3+ ions by weak magnetic Cr 3+ ions at the octahedral site. Decrement observed in coercivity from 0.085T to 0.044 T at room temperature with increase in Cr concentration is indicative of the decrement in the isotropic field. Coercivity follows the Kneller's law for Co 0.5 Mg 0.5 Fe 2 O 4 ferrite within the temperature range 5–300 K. Interestingly the saturation magnetization was observed to increase whereas the coercivity decreases with increase in the annealing temperature in Co 0.5 Mg 0.5 Cr 0.6 Fe 1.4 O 4 ferrite.