Synthesis, structural and magnetic characterization of iron-zinc-borate glass ceramics containing nanocrystalline zinc ferrite

Two different glass ceramics with the composition of the (Fe2O3)x·(B2O3)(60−x)·(ZnO)40, where x = 12.5 and 15 mol%, have been synthesized using the melt-quench method. The X-ray diffraction (XRD) patterns show the presence of nanometric zinc ferrite (ZnFe2O4) crystals, with spinel structure, in a glassy matrix after cooling from melting temperature. The estimated amount of crystallized zinc ferrite varies between 16 and 35%, as a function of the chemical composition. Glass transition (Tg), crystallization (Tp) and melting (Tm) temperatures were determined by differential thermal analysis (DTA) investigations. Fourier transform infrared (FTIR) data revealed that the BO3 and BO4 are the main structural units of these glass ceramics network. FTIR spectra of these samples show features at characteristic vibration frequencies of ZnFe2O4. Electron paramagnetic resonance (EPR) measurements show the presence of isolated Fe3+ ions predominantly situated in rhombic vicinities and as well as the Fe3+ species interacting by dipole–dipole interaction or to their superexchange coupled pairs in clustered formations. The magnetic properties of the studied glass ceramics were investigated by vibrating sample magnetometer (VSM). From the magnetization curves for glass ceramic containing 15 mol% Fe2O3 it was found that the nanoparticles exhibit ferromagnetic interactions combined with superparamagnetism with a blocking temperature, TB. For studied samples the hysteresis is present. The coercive field is dependent on composition and magnetic field being around 0.05 μB/f.u for measurements performed in maximum 0.4 T.