Effect of cation distributions on structural and magnetic properties of Ni_(1-x)Co_xFe_2O_4 spinel ferrites

摘要

Single-phase polycrystalline samples of Ni_(1-x)Co_xFe_2O_4 (x = 0 - 0.50) were prepared by sol gel method and their structural and magnetic properties were studied. Room temperature X-ray diffraction patterns and Rietveld refinement confirm cubic crystal structure (Fd3m). The lattice constant, saturation magnetization, magnetic anisotropy constant and coercivity of the samples are found to increase with Co concentration. An analytical quantum mechanical method was used to estimate the cation distributions in the prepared samples with the help of measured magnetic moment at T = 5 K. Even though, most of the doped Co ions occupy the octahedral site, considerable distribution of Co~(2+) ions at tetrahedral site is noticed. The observed magnetization is explained based on cation distribution worked out from quantum mechanical method. The red shifting of Raman active mode A_(1g) and ESR results further confirm the presence of divalent cations in the tetrahedral sites.