EPR AND MAGNETIC-SUSCEPTIBILITY STUDIES OF IRON IONS IN 70TEO(2).25B(2)O(3).5PBO GLASS MATRIX

Results of EPR and magnetic susceptibility measurements performed on x Fe(2)O(3) .(1-x)[70TeO(2) . 25B(2)O(3) . 5PbO] glasses with 0 < x less than or equal to 20 mol.% are reported. EPR data suggest a tetragonal ly distorted octahedral symmetry for Fe3+ ions. The changes induced in the resonance spectra by increasing of Fe2O3 content are explained su pposing that the resonance centered at g approximate to 2.0 is due to clustered ions. The composition dependence of g approximate to 2.0 lin e-width shows prevailing superexchange interactions for x > 1 mol.%. T he spectra of the investigated glasses containing up to 3 mol.% Fe2O3 presents in addition to the line at g approximate to 4.3 also a weak r esonance line at g approximate to 9.79 that denotes the rhombic charac ter of the structural units involving the resonance centers. The param agnetic resonance data consists with those obtained from magnetic meas urements. The Curie constant values indicate that in this glass system the iron ions are in both Fe3+ and Fe2+ valence state, the last one r epresenting about 56% from the total iron ions content. For x greater than or equal to 1 mol.% a micromagnetic type order was evidenced. (C) 1997 Elsevier Science Ltd.