DIRECT MEASUREMENT OF OCTAHEDRAL AND TETRAHEDRAL SITE ENVIRONMENTS INNIZN-FERRITES

The local environment of metal ions in a series of spin-sprayed Ni0.15 ZnyFe2.85-yO4 (y = 0.16, 0.23, 0.40, 0.60) films have been studied usi ng extended x-ray absorption fine structure (EXAFS). Fourier transform s of the EXAFS data illustrate peaks which are identified with specifi c local atom correlations within the spinel ferrite unit cell. From th ese data the relative occupancy of the cations on the octahedral and t etrahedral sites are determined. We find that Ni ions occupy the octah edral sites, while the Zn ions occupy the tetrahedral sites. Fe cation s occupy both sites in a ratio determined by the Zn/Fe ratio. The vale nce distribution of Fe ions on these sites is consistent with that of an inverted spinel. The saturation magnetization varies with increasin g Zn/Fe ratio, first increasing due to the imbalance on the Fe spin la ttice and later decreasing due to the disruption of the A-B superexcha nge.