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 (ZnFe₂O₄) thin film prepared by a sputtering method, ZnFe₂O₄ thin films annealed at elevated temperatures, and ZnFe₂O₄ 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 8000.2em0ex^∘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-x²⁺Feₓ³⁺]A[Znₓ²⁺Fe_2-x³⁺]BO₄, 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.