EBSD investigation and magnetic properties of manganese ferrite crystallized in a sodium-silicate glass

Glasses were prepared in the system (100-x)(0.16Na(2)O/0.10MnO/0.74SiO(2))/xFe(2)O(3) (x = 15 and 25 in mol%) by the traditional melt-quenching technique. Some of them were subsequently crystallized at temperatures in the range from 520 to 700 degrees C for times from 10 min to 100 h. The valence states of Fe and Mn in selected glasses and glass-ceramics were investigated by X-ray photoelectron spectroscopy (XPS) and showed the presence mostly of Mn2+ while Fe occurs as both Fe2+ and Fe3+. X-ray diffraction (XRD) analyses of the 15 mol% Fe2O3 samples revealed that at lower temperatures and for short heat treatment times a solid solution with a spinel structure and a chemical composition between MnFe2O4 (jacobsite) and Fe3O4 (magnetite) crystallizes, while aegirine (NaFe(SiO3)(2)) additionally occurs at higher temperatures and for longer annealing times. Here the average crystallite size of the jacobsite-based phase varies between 4 and 10 nm, as determined by XRD. The XRD analysis of the 25 mol% Fe2O3 samples which spontaneously crystallize when quenching the melt only show the precipitation of the jacobsite-magnetite solid solution. The microstructure was investigated by scanning and transmission electron microscopy (SEM and TEM) as well as electron-backscatter diffraction (EBSD). The EBSD analyses show that the cubic crystals grow via the polygon as well as the dendritic growth mechanisms. The individual grains show independent orientations and inclusions of residual glass while a global crystallographic texture could not be detected. The obtained magnetization curves of the 25 mol% Fe2O3 samples show hysteresis and a Curie temperature of approximately 480 degrees C which supports the XRD results. The samples with 15 mol% Fe2O3 crystallized at 650 and 700 degrees C exhibit superparamagnetic behaviour and thin S-shaped magnetization curves with zero coercivity.