Role of Fe-Doping on Structural, Optical and Magnetic Properties of SnO2 Nanoparticles

We have investigated the influence of Fe doping (1 at.% and 2 at.%) on the structural, optical and magnetic properties of SnO2 nanoparticles (NPs) synthesized via co-precipitation route. Rietveld refinement of x-ray diffraction results confirmed the successful substitution of Fe ions into the SnO2 rutile crystal structure without secondary phase. The crystallite sizes increased with an increase in Fe concentration and were found to be in the range of 9–26 nm. Field-emission scanning electron microscopy results revealed that the doping of Fe ions enhances the agglomeration of the grains and consequently cluster formation takes place with uniformly dispersed spherical-like morphology. Hence, the statistical distributions of NP sizes were in the range of 20–25 nm and 40–60 nm for 1 at.% and 2 at.% Fe doping, respectively. Energy dispersive x-ray spectra confirmed the elemental ratios present in the samples. Raman spectral features elucidated that the variation in Fe concentration induces a change in the oxygen stoichiometry and enhances the formation of oxygen vacancies (Ov).The magnetization investigation showed that pure SnO2 is a nonmagnetic compound even in the presence of Ov that has been proven theoretically based on density functional theory calculations, whereas the Fe (1 at.% and 2 at.%)-doped SnO2 NPs showed a weak ferromagnetic signal. Our study confirmed that the FM in pure SnO2 NPs (d0-magnetization) is not possible and that the Fe dopant ions are responsible for the observed ferromagnetic state. The role of Fe doping and surface Ov has been discussed based on the bound magnetic polaron mechanism.