Direct evidence for weak ferromagnetism sustained by Fe2<b>+</b>–O–Fe3<b>+</b> superexchange coupling in short-range structures of aluminosilicate glasses
Raí F. Jucá, J.M. Soares, V. A. Soares, Diego S. Evaristo, Francisco G. S. Oliveira, Igor F. Vasconcelos, Gilberto D. Saraiva, Nilson S. Ferreira, M.A. Macêdo
Abstract
We report on the magnetism of amorphous SiO2–Al2O3–CaO–MgO–Fe2O3–K2O–MnO:CA (CA—activated carbon) aluminosilicate glasses prepared by a fusion-quenching method. Fourier transform infrared and Raman spectroscopy show that a Fe2+ lattice modifier in the glass structures induces depolymerization, strongly influencing the magnetic transitions. Room temperature magnetization measurements of the CA-glasses show a different magnetic behavior, such as speromagnetism, asperomagnetism, and weak ferromagnetism. Mössbauer spectroscopy analyses at room temperature reveal that iron changes valence from Fe3+ → Fe2+ with increasing CA content. This Fe3+ → Fe2+ suggests that asperomagnetism and weak ferromagnetism behavior are triggered by Fe2+–O–Fe3+ superexchange coupling in short-range structures of aluminosilicate glasses. A model for the aluminosilicate glass structures is proposed to explain the different magnetic regimes.