Direct evidence for weak ferromagnetism sustained by Fe2+–O–Fe3+ superexchange coupling in short-range structures of aluminosilicate glasses

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.