The influence of the heat treatment temperature in the magnetic characteristics of a SiO2–Li2O–Fe2O3 glass prepared by sol-gel

• A transparent glass (88SiO2–2Li2O–10Fe2O3, mol%) was well prepared by sol-gel;
• Precipitation of LiFe5O8 crystallites gives rise to a ferrimagnetic glass ceramic.
• Paramagnetic behavior at RT condition was observed;
• Superparamagnetism of α-Fe2O3 due to crystallites with size < 10 nm was detected;
• With annealing, a hyperfine field arises and a relaxation is observed.

The glass with the molar composition 88SiO2–2Li2O–10Fe2O3 (mole %) was prepared by the sol-gel route and after heat-treated at temperatures between 250 and 1000 °C under oxidizing conditions. Crystalline phases (LiFe5O8, SiO2, Fe2O3 and LiFe(Si2O6)) were observed by X-ray powder diffraction in the glasses treated at temperatures above 800 °C. Scanning electron micrographs reveal the presence of particles in the samples heat-treated up to 800 °C, which are essentially amorphous or with an incipient crystallization. The increase of the heat-treatment temperature promotes the coarsening of particles.The magnetic characteristics of the prepared glasses and glass ceramics were performed using a vibrating sample magnetometer in function of the magnetic field amplitude (− 10 T ≤ B ≤ 10 T) and in function of temperature (5 K–300 K). The samples heat-treated at 900 and 1000 °C present a ferrimagnetic behavior accompanied by the appearance of peaks corresponding to the lithium ferrite phase (LiFe5O8). A curious aspect is the saturation magnetization of the sample heat-treated at 800 °C is the highest of all samples, indicating the highest amount of LiFe5O8 crystals. The Mossbauer results are in accordance with the magnetization and magnetic susceptibility measurements.