Structural and magnetic properties of nanocrystalline Zn0.65Ni0.35Fe2O4 powder obtained from heteropolynuclear complex combination

The nanocrystalline Zn0.65Ni0.35Fe2O4 mixed ferrite with a mean diameter between 37.0 and 68.1 nm was obtained from the heteropolynuclear complex combination Fe2(Zn,Ni)(OH)4(C2H2O4)2·nH2O, having as ligand the C2H2O42− glyoxylate dianion. The thermal decomposition process of the complex combination was investigated by DTA–TG techniques. After thermal decomposition at 350 °C, the resulting ‘residue’, composed of a quasi-amorphous mixture of oxides, was annealed for 2 h within the 900–1300 °C temperature range. By X-ray diffraction (XRD), it was shown that the resulting powder was made up of a single phase of Zn–Ni ferrite nanocrystals with fcc structure and a lattice constant in agreement with the known value. The magnetic measurements showed the increase of the specific saturation magnetization σs as well as the decrease in both coercivity Hc and remanence ratio r of the nanocrystallites with the increase of the annealing temperature. This behavior was correlated with the increase of the mean diameter of the nanocrystallites above a critical value (dcr), (under this critical value the particles can be considered as single domain). The model calculation for the critical diameter is in agreement with the experimental results.