Microstructure and magnetic properties of substituted (Cr, Mn) - cobalt ferrite nanoparticles

Three mixed ferrite systems CoFe2O4, CoCr0.2Fe1.8O4 and CoMn0.2Fe1.8O4 were prepared by the co-precipitation method. X-ray diffraction (XRD) of the calcined powders at 900 °C confirms the accomplishment of the cubic spinel phase formation without any secondary phase. The cation distribution was determined from XRD data and suggested a mixed spinel structure. The higher value of the lattice parameter for Mn comparing with Cr substituted cobalt ferrite could be explained by migration of Co2+ cation from octahedral to tetrahedral sites. Infrared spectroscopy (FTIR) showed two absorption bands attributed to intrinsic vibrations of tetrahedral and octahedral complexes. The bands shifted toward lower frequency for doped samples comparing with corresponding Co-host ferrite frequencies. The microstructure was investigated by scanning electron microscopy (SEM) and suggested that the nanoparticles are agglomerated and have polygonal faced surfaces. The effect of Mn3+ and Cr3+ cation distribution among the tetrahedral (A) - and octahedral [B] - sites of Co substituted ferrite on magnetization and coercive field was investigated by vibrating sample magnetometer technique. Higher values of the coercive field of manganese and chromium substituted cobalt ferrite was explained by lower value of the average particle size. The small increase of saturation magnetization for doped ferrites was explained considering the oxidation state of the substituting ions.

► The influence of manganese and chromium substitutions on the coprecipitated cobalt ferrite nanoparticles is described.
► The microstructure of the as synthesized powders is correlated with the substitution.
► Development of the spinel phase enhanced by thermal treatment is monitored by FTIR and XRD analyses.
► The magnetic properties of the mixed ferrites are correlated with phase content and cation distribution.
► The influence of the annealing process on the magnetic properties of the mixed ferrites is discussed.