Structural and magnetic properties of sodium iron germanate glasses

A series of sodium iron germanate glasses, with general composition 0.3Na(2 )O-xFe(2)O(3)-(0.7 - x)GeO2 (0 less than or equal to x less than or equal t o 0.15), has been prepared by conventional melting and casting. The chemica l states of the various elemental components have been investigated by X-ra y 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, w ith the proportion of the Fe3+ ions found to increase with increasing Fe2O3 content. The O 1s spectra also show composition-dependent changes, with th e fraction of non-bridging oxygen atoms also increasing with iron oxide con tent. Direct current magnetic susceptibility and magnetisation (M) vs magne tic field (H) measurements were also performed on the same samples. The mag netic data support the conclusion that the exchange interaction is antiferr omagnetic and increases with increasing Fe2O3 content. The fraction of Fe2 ions determined from XPS was found to be in good agreement with values obt ained from fitting the M vs H data with a standard Brillouin function. (C) 2000 Elsevier Science B.V. All rights reserved.