Oxygen vacancy-mediated room temperature ferromagnetism in Sr-doped SnO2 nanoparticles

Sn1−xSrxO2 nanoparticles (NPs) were synthesized by the sol–gel method in the present work. X-ray diffraction analyses reveal that Sr atoms are incorporated into the SnO2 NPs without forming secondary phase with Sr concentration up to 5 at.%. The room temperature photoluminescence measurements indicate that Sr doping increases the number of singly charged oxygen vacancies (VO+) in SnO2 NPs due to the different ionic radii of Sr2+ and Sn4+. Both pure and Sr-doped SnO2 NPs are ferromagnetic and the largest saturation magnetization of 6.98 × 10−4 emu/g has been observed in Sn0.95Sr0.05O2 NPs which has the largest concentration of VO+ defects. The correlation between the induced VO+ defects and the enhanced ferromagnetism implies that the observed ferromagnetic ordering in Sn1−xSrxO2 NPs is connected with VO+ defects. Meanwhile, air-annealing of the samples resulting in a significant suppression of the ferromagnetism further supports this point.