EPR and magnetic susceptibility studies of manganese ions in Bi2O3-GeO2 glasses

EPR and magnetic susceptibility measurements performed on xMnO .(1-x)[Bi2O3 . GeO2] glasses with 0 < x less than or equal to 50 mol.% are reported. The EPR spectra are modified with the increase of manganese ions content. In the concentration range 0 < x less than or equal to 30 mol.% the spectra are characterized by the appearance of two resonance lines at g congruent to 4.3 having a resolved hyperfine structure for 0 < x less than or equal to 1 mol.%, characteristic for isolated Mn2+ ions in low-symmetric sites and g congruent to 2.0 without hyperfine structure characteristic to clustered Mn2+ ions. The Delta B values of g congruent to 2.0 resonance lines and magnetic susceptibility data suggest the appearance of superexchange interactions for x greater than or equal to 30 mol.%. From the Curie constant values we have established that in these glasses both Mn2+ and Mn3+ ions are present, determining their magnetic behaviour. (C) 1998 Elsevier Science Ltd.