Effect of annealing time on structural, optical and magnetic properties of TiO2 nanoparticles

The structural, optical and magnetic behavior of undoped TiO2 nanoparticles synthesized by sol-gel technique annealed at 400 °C in air for different time periods were studied. Tetragonal anatase phase was formed in all the samples as studied from X-ray diffraction, and Raman spectroscopy. HRTEM showed the particles in the nanometer range (13–16 nm) Photoluminescence and XPS show the formation of oxygen vacancies and Ti3+ions. Clear hysteresis is observed at low field, but there is a lack of saturation magnetization, suggesting the presence of paramagnetic/diamagnetic contributions. The bound magnetic polaron (BMP) is proposed to be the mechanism of ferromagnetism (FM) which is formed by overlapping of orbital of trapped electrons in F+ center with the unpaired (3d1) electron of Ti3+ions. The increase of magnetic moment with the increase in annealing time can be due to a greater number of BMPs participating in FM exchange and the same have formed due to the formation of large number of oxygen vacancies and Ti3+ ions in TiO2 nanocrystals. •Magnetic behavior of TiO2 nanoparticles based on BMP model associated with the oxygen vacancy defects is explained.•RTFM is observed to be enhanced with the annealing time.•This work would be of interest to scientific community working in the field of spintronics and magneto-optic devices.