Annealing dependent oxygen vacancies in SnO2 nanoparticles: Structural, electrical and their ferromagnetic behavior

The effect of annealing on structural, electrical and d0 ferromagnetism in SnO2 nanoparticles synthesized by solution combustion method is investigated. The as synthesized SnO2 nanoparticles were annealed at 500 °C-1300 °C for 2 h in ambient conditions. The crystallinity, grain size and morphology of the samples were studied using X-ray diffraction, Field emission scanning electron microscope, Transmission electron microscopy and energy dispersive X-ray spectroscopic studies. The annealing temperature resulted in grain growth as well as reduction in oxygen vacancies as confirmed by Raman spectroscopy. Resistivity measurement of all the samples showed the typical behavior of semiconductors. Dielectric spectroscopy showed that there is an improvement in electric properties of SnO2 nanoparticles as the annealing temperature is increased. The samples exhibited ferromagnetism at room temperature as well as at 5 K. However, the saturation magnetization at room temperature is decreasing from 0.019 emu/g to 0.001 emu/g whereas at 5 K, it is decreasing from 0.75 emu/g to 0.05 emu/g with increasing annealing temperature. The observed difference between ferromagnetism at 300 K and 5 K clearly indicates that oxygen vacancies become more active at 5 K and induce ferromagnetism with almost 40 times higher magnitude of saturation magnetization than that at 300 K in as synthesized and annealed SnO2 nanoparticles. In the light of this study electrical and magnetization values can be tuned by changing the relative concentration of oxygen vacancies which can be achieved by varying annealing temperature thus projecting their technological applications in spintronics.