Band gap widening and d0 ferromagnetism in epitaxial Li-doped SnO2 films

Epitaxial grown Li doped SnO2 films with room temperature d0 ferromagnetism were prepared by radio frequency magnetron sputtering. X-ray diffraction and X-ray photoelectron spectroscopy give clear evidence of Li presence at both substitutional and interstitial sites. A conversion of conductivity from n-type to p-type was observed as the Li concentration reaches 6 at.%. The band gap of films increased non-montonically with the Li concentration. All the films are ferromagnetic, and the largest saturation magnetization of 7.9 emu/cm3 is observed in the Sn0.88Li0.12O2 film which has the widest band gap. The consistency of the variation between the magnetic, structural, electrical and optical properties indicates that holes introduced by Li substitutions can enhance the ferromagnetism though p-p interaction.