Structural and Magnetic Property of Cr³⁺ Substituted Cobalt Ferrite Nanomaterials Prepared by the Sol-Gel Method

Cobalt-chromium ferrite, CoCrFe_2-O₄ (x = 0⁻1.2), has been synthesized by the sol-gel auto-combustion method. X-ray diffraction (XRD) indicates that samples calcined at 800 °C for 3 h were a single-cubic phase. The lattice parameter decreased with increasing Cr concentration. Scanning electron microscopy (SEM) confirmed that the sample powders were nanoparticles. It was confirmed from the room temperature Mössbauer spectra that transition from the ferrimagnetic state to the superparamagnetic state occurred with the doping of chromium. Both the saturation magnetization and the coercivity decreased with the chromium doping. With a higher annealing temperature, the saturation magnetization increased and the coercivity increased initially and then decreased for CoCr_0.2Fe_1.8O₄.