Ferromagnetic behaviour of vanadium doped SnO2 nanoparticles annealed at different temperatures

• Sn1−xVxO2 nanoparticles annealed at different temperatures were prepared.
• The crystallites sizes were estimated by XRD.
• V2O5 phase was evidenced by Raman spectroscopy in samples annealed at 800, 1000 °C.
• A ferromagnetic behaviour for the undoped SnO2 sample was obtained.
• The ferromagnetism is enhanced by doping with V ions and annealing at 450 °C.

A series of Sn0.99V0.01O2 powders were prepared and annealed at different temperatures: 450 °C, 600 °C, 800 °C, 1000 °C. The XRD measurements confirm the substitution of Sn4+ ions by vanadium ions. A secondary phase of V2O5 was evidenced by Raman spectroscopy only in the samples annealed at 800 and 1000 °C. The FTIR spectroscopy reveals the presence of oxygen vacancies. By XPS spectroscopy was evidenced the presence of four valence states for vanadium ions. The relative concentrations of these ions are influenced by annealing temperature. The EPR spectra for the samples annealed at 450 °C and 600 °C show a well resolved hyperfine structure composed of two sets of eight lines which is typical of the unpaired 3d1 electron of 51V (I = 7/2) in an axially distorted crystal field. At higher annealing temperature a superhyperfine structure due to the interaction with tin nuclei was observed. A ferromagnetic behaviour, probably due to the oxygen vacancies, was evidenced for the samples annealed at 450 °C and 600 °C.