Crystallographic Effects of Larger Indium Ion Substitution in NiFe_2-xIn_xO₄(x = 0, 0.2, 0.5, and 1.0) System

The crystallographic and magnetic properties of a series of substitutions in nickel ferrite where the Fe³+ is replaced with In³+ have been investigated using X-ray diffraction (XRD) and Mossbauer spectroscopy. Information on the exact crystalline structure, lattice parameters, bond lengths and bond angles were obtained by refining their XRD profiles by a Rietveld method. All the crystal structures were found to be cubic with the space group Fd/3m. The lattice constants increased with In³+ concentration. The expansion of the tetrahedron was outstanding, indicative of the tetrahedral (A) site preference of larger indium ion. The Mossbauer spectra showed two sets of sextuplet originating from ferric ions occupying the tetrahedral sites and the octahedral (B) sites under the Neel temperature T_N. Regardless of the composition x, the electric quadrupole splitting was zero within the experimental error. At x = 0.2, the magnetic hyperfine fields increased slightly, which meant that the nonmagnetic indium ions occupied preferentially the A-site. At the same time, the intensity of the B-site subspectra decreased markedly at the elevated temperature, indicating that the occupation of the A site by indium induced a considerable perturbation on the B site.