Direct measurement of octahedral and tetrahedral site environments in NiZn-ferrites

The local environment of metal ions in a series of spin-sprayed Ni _0.15Zn_yFe_2.85-yO₄ (y=0.16, 0.23, 0.40, 0.60) films have been studied using extended X-ray absorption fine structure (EXAFS). Fourier transforms of the EXAFS data show peaks which are identified with specific local atom correlations within the spinel ferrite unit cell. From the data the relative occupancy of the cations on the octahedral and tetrahedral sites are determined. We find that Ni ions occupy the octahedral sites, while the Zn ions occupy the tetrahedral sites. Fe cations occupy both sites in a ratio determined by the Zn/Fe ratio. The valence distribution of Fe ions on these sites is consistent with that of an inverted spinel. The saturation magnetization varies with increasing Zn/Fe ratio, first increasing due to the imbalance on the Fe spin lattice and later decreasing due to the disruption of the A-B superexchange