Influence of Oxygen Flow Rate on the Morphology and Magnetism of SnO2 Nanostructures

Room-temperature ferromagnetism has been observed in undoped SnO2 nanostructures with various morphologies synthesized by a chemical vapor deposition (CVD) method. The magnetization depends on the oxygen flow rate during the CVD synthesis and decreases monotonically with the increase of the oxygen flow rate. X-ray diffraction and X-ray photoelectron spectroscopy measurements show that all the samples possess a typical rutile structure, and no other impurity phases are observed. Photoluminescence and X-ray photoelectron spectroscopies were employed to evidence the presence of oxygen vacancies in these samples and reveal that the oxygen vacancies contribute to the ferromagnetism. To further test the oxygen-vacancy-related ferromagnetism, post-thermal annealing in different ambiances was performed. The results confirm that the oxygen vacancies, not Sn interstitials, play a crucial role in inducing the ferromagnetism in undoped SnO2 nanostructures.