Electronic and magnetic properties of Co3 O4 and Co3−xNixO4 from theoretical XANES spectroscopy at the Co K-edge

We present theoretical XANES spectroscopy at the Co K-edge, combined with DFT+U calcula-tions, to investigate the electronic and magnetic properties of Co3 O4 normal spinel and the nickel doped system Co3−x Nix O4 . Two configurations have been considered for the nickel doped system : the configurations in which one nickel atom substitutes a tetrahedral and an octahedral cobalt, respectively. The Co K-edge XANES spectrum shows two pre-peaks in Co3O4 normal spinel, while only one pre-peak is observed in the cases of doped systems. We attribute the disapearance of one pre-peak in the doped systems to the shift toward high energies of tetrahedral cobalt 3d empty states. We demonstrated that, nickel doping causes the oxidation state of tetrahedral cobalt to increase slightly, while that of octahedral cobalt remains almost unchanged. Moreover, nickel possesses a magnetization when substituting octahedral cobalt, and contributes to render Co3O4 a half metal system, while this magnetization decreases when nickel substitutes a tetrahedral cobalt.