Effect of nickel content on structural, morphological and magnetic properties of Ni x Co1-x Fe2O4/SiO2 nanocomposites

Ni_xCo_1-xFe₂O₄/SiO₂ nanocomposites (x = 0, 0.25, 0.50, 0.75 and 1.00) were synthetized by a modified sol-gel method. The X-ray diffraction (XRD) patterns revealed the crystalline phases and the crystallite size variation with increasing annealing temperature and Ni content. The lattice constants, cell volume, X-ray density, hopping length in A and B sites, average crystallites size and relative crystallinity calculated from XRD data are consistent with the mixed spinel structure. The transmission electron microscopy images reveal the spherical shape of nanoparticles and their size increase with increasing annealing temperature. The magnetic properties such as saturation magnetization (M_s), remanent magnetization (M_r), coercivity (H_c), magnetic moments per unit cell (n_B) and anisotropy (K) decrease with increasing Ni content, but they increase with the annealing temperature due to the influence of the cation stoichiometry and their specific sites occupancy. The Mössbauer spectra showed the characteristic magnetic patterns of Co and Ni spinels and revealed only the presence of Fe³⁺. The Ni-rich nanocomposites presented superparamagnetic behavior, while the Ni-poor nanocomposites ferromagnetic behavior.