Magnetic susceptibility and NEXAFS, EPR spectra of co-doped Bi3NbO7

The methods of NEXAFS, EPR spectroscopy and static magnetic susceptibility were used to analyze the condition and nature of exchange interaction of paramagnetic cobalt atoms within the bismuth niobate Bi3NbO7 matrix. The samples of Bi3Nb1-xCoxO7-δ with cubic fluorite-like structure were synthesized by the solid-phase method; their microstructure and magnetic properties were studied. The samples had monolithic, non-porous solid microstructure without clear crystal boundaries. The results of the magnetic susceptibility and NEXAFS studies showed that cobalt atoms in the solid solutions were predominantly represented by Co(II) and Co(III) high-spin atoms and their exchange-coupled aggregates with the antiferromagnetic type of exchange. The magnetic moment of cobalt atoms in the solid solutions exceeded the pure spin values for Co(II)s=3/2 and Co(III)s=2, and ranged from 6.12 to 7.15 μB. The analysis of the NEXAFS Co2p-spectra of the cobalt-doped solid solutions and cobalt oxides revealed that the studied Co atoms were mainly in the +3 and +2 oxidation states. Only one component was reliably established in the recorded EPR spectra. This was an asymmetric broad band with the g factor of about 4. This signal could be attributed to the high-spin state (S = 3/2) of Co(II).