Crystallization behaviour and magnetic properties of sodium-silicate glasses containing iron and manganese oxide

Oxide glasses and nanocrystalline glass-ceramics, containing large amounts of transition metal ions, exhibit novel and unusual electrical and magnetic properties and find various applications in magnetorheology, electronics, magnetic resonance imaging and sensor technology. The present work is dedicated to the study of the crystallization behaviour, phase formation and the resulting magnetic properties of the synthesized products in the system Na2O/MnO/SiO2/Fe2O3. Two glasses with 15 mol% Fe2O3-concentration and different MnO concentrations are prepared by melting under oxidizing or reducing conditions. Further, the glasses are annealed by applying different time/temperature programs in order to precipitate nano-scale magnetic crystals. The phase composition and microstructure of the glass-ceramics are studied by X-ray diffraction and electron microscopy. The obtained data are used to reveal the crystallization kinetics. The magnetic properties of the selected samples, measured on a vibrating sample magnetometer, vary from para- to superparamagnetic.