Influences of Postannealing Treatment Parameters on the Structural and Magnetic Properties of Nickel-Doped Cobalt Ferrite Synthesized by Sol-Gel Route

We prepared and characterized nickel-substituted cobalt ferrite (Ni_0.1Co_0.9Fe₂O₄) nanoparticles using the sol-gel method. The physical properties of the nanoparticles have been modified by postannealing treatment at atmo-spheric conditions. X-ray diffraction results confirmed that the nanoparticles possessed a single-phase face-cen-tered cubic crystalline structure. The crystallite sizes increased from 20.85 to 26.06 nm with the increased annealing temperature. Transmission electron microscopy results confirmed the crystal structure of the nickel-substituted cobalt ferrite nanoparticles. Furthermore, Fourier-transform infrared spectroscopy results showed that the typical characteristic absorption of the nanoparticles was obtained at wave numbers k = 575 and 374 cm⁻¹. Finally, the saturation magnetization and coercivity of the nanoparticles increased with the annealing temperature, which is attributed to the increase in magnetic anisotropy constant.