Structure and Magnetic Properties of Nanosized Magnetite Obtained by Glass Recrystallization

We present the preparation, structural and magnetic properties of nanosized magnetite obtained by the crystallization of a series of Fe-containing borosilicate glasses. Several compositions with the ratio Fe₂O₃/SiO₂ spanning from 0.37 to 0.67 were investigated as a function of two nucleators Cr₂O₃ and P₂O₅, respectively, and modifiers and intermediates (Al₂O₃ and MgO). Mössbauer spectroscopy revealed the degree, the type and the location of disorder induced by a specific composition and nucleators. In addition to magnetite, it was also revealed the presence of large amounts of Fe-rich paramagnetic phases. The magnetic response is analysed in relation with the amount of Fe ions which remain dispersed in the glassy matrix as noninteracting (paramagnetic) ions. We discuss the role of the nucleators on the disorder in both tetrahedral and octahedral sites of the magnetite.