First-principles XANES simulations of spinel zinc ferrite with a disordered cation distribution

Theoretical calculations of Zn K and Fe K x-ray absorption near-edge structures (XANES) using a first-principles method have been performed to evaluate the degree of cation disordering in spinel zinc ferrite (Zn Fe2 O4) thin film prepared by a sputtering method, Zn Fe2 O4 thin films annealed at elevated temperatures, and Zn Fe2 O4 bulk specimen prepared by a solid-state reaction. Using the full-potential linearized augmented plane-wave + local orbitals method, a theoretical spectrum is generated for the tetrahedral and octahedral environments for each of the two cations. The experimental XANES spectrum of the thin film annealed at 800°C as well as that of bulk specimen is successfully reproduced by using either the theoretical spectrum for Zn2+ on the tetrahedral site (A site) or that for Fe3+ on the octahedral site (B site), which is indicative of the normal spinel structure. For the as-deposited film, on the other hand, excellent agreement between theoretical and experimental spectra is obtained by considering the presence of either ion in both the A and B sites. The degree of cation disordering, x, defined as [Zn 1-x 2+ Fex 3+] A [Znx 2+ Fe 2-x 3+] B O4, is estimated to be approximately 0.6 in the as-deposited film, which is consistent with the analysis of the extended x-ray absorption fine structure on the Zn K edge. Curious magnetic properties as we previously observed for the as-deposited thin film-i.e., ferrimagnetic behaviors accompanied by large magnetization at room temperature and cluster spin-glass-like behavior-are discussed in connection with disordering of Zn2+ and Fe3+ ions in the spinel-type structure.