Structural and magnetic properties of sodium iron germanate glasses

A series of sodium iron germanate glasses, with general composition 0.3Na2O–xFe2O3–(0.7 − x)GeO2 (0⩽x⩽0.15), has been prepared by conventional melting and casting. The chemical states of the various elemental components have been investigated by X-ray photoelectron spectroscopy (XPS) from fracture surfaces produced in situ. The analysis of the Fe 3p core level spectra of the glasses which contain iron oxide revealed the presence of both Fe2+ and Fe3+ oxidation states, with the proportion of the Fe3+ ions found to increase with increasing Fe2O3 content. The O 1s spectra also show composition-dependent changes, with the fraction of non-bridging oxygen atoms also increasing with iron oxide content. Direct current magnetic susceptibility and magnetisation (M) vs magnetic field (H) measurements were also performed on the same samples. The magnetic data support the conclusion that the exchange interaction is antiferromagnetic and increases with increasing Fe2O3 content. The fraction of Fe2+ ions determined from XPS was found to be in good agreement with values obtained from fitting the M vs H data with a standard Brillouin function.