Size-dependent dielectric behaviour of magnetic Gd2O3 nanocrystals dispersed in a silica matrix

Magnetic nanocrystalline Gd2O3 particles have been successfully synthesized in a silica glass matrix by the sol–gel method at calcination temperatures of 700 °C and above. The optical spectra, corresponding to the transition from ground 8S7/2 to the excited 6P, 6I and 6D multiplets, show a large blue shift which increases with decreasing particle size. Calculated free ion parameters represent different electrostatic and spin–orbit interactions of nanocrystalline Gd2O3 compared with the bulk Gd2O3. The thermal behaviour of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of Gd2O3 nanocrystals in the 5–300 K temperature interval have demonstrated that the Gd2O3 nanocrystals present in these glasses display superparamagnetic–ferromagnetic transition at low temperatures. The present Gd2O3 nanoparticles embedded in the silica glass matrix show a high (~103) dielectric constant with considerable low loss and good temperature-independent character associated with an important technological implication which promises wide applications in memory devices.