Structural, Electronic, and Magnetic Properties and Hyperfine Interactions at the Fe Sites of the Spinel TiFe₂O₄. Ab Initio, XANES, and Mössbauer Study

We present here an experimental and theoretical study of the Ti-ferrite (TiFe₂O₄, ulvospinel). The theoretical study was performed in the framework of density functional theory using the full-potential linearized augmented plane waves method and employing different approximations for the exchange and correlation potential. In order to discuss the magnetic ordering and the electronic structure of the system, we considered different distributions of the Fe/Ti atoms in the two cationic sites of the structure and, for each distribution, different spin arrangements (ferromagnetic, ferrimagnetic and antiferromagnetic cases). We found that the equilibrium structure corresponds to an inverted spinel structure with an antiferromagnetic spin configuration in which the magnetic moments of the Fe ions in both A and B sublattices are ferromagnetically ordered, while the magnetizations of these two sublattices are antiparallel with respect to each other. Our calculations predict that TiFe₂O₄ is a wide-band gap semiconductor (band gap in the order of 2.3 eV) and successfully describe the hyperfine properties (isomer shift, magnetic hyperfine field, and quadrupole splitting) at the Fe sites that are seen by Mossbauer spectroscopy (MS) experiments at 4.2 K reported in the literature and MS performed at 300 K in the present study. We also measured and simulated the X-ray absorption near-edge spectroscopy (XANES) spectra of TiFe₂O₄ at both Ti and Fe K-edges. Our calculations correctly reproduce the XANES spectra and enable us to separate the contribution of each site to the experimental spectra. All these studies enable us to obtain a complete structural, electronic, magnetic, and hyperfine characterization of TiFe₂O₄.