Magnetic behavior and nexafs-spectroscopy of Bi$_2$BaNb$_{2-2x}$Сo$_{2x}$O$_{9-\delta}$

The samples of solid solutions of Bi$_2$BaNb$_{2-2x}$Сo$_{2x}$O$_{9-\delta}$ composition at $x \leqslant 0.04$ were synthesized by the solid-phase method. The electron state and the nature of the exchange interactions of cobalt atoms in the samples were studied by the measurements of magnetic susceptibility and NEXAFS-spectroscopy. The NEXAFS spectra of the solid solutions and the cobalt oxides CoO, Co$_3$O$_4$ were recorded. According to the data of X-ray spectroscopy and magnetic susceptibility, the charge states of cobalt atoms in the solid solutions were identified as Co(II) and Co(III) in the forms of monomers and exchange-bound aggregates with the antiferromagnetic type of exchange.