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

Highlights: • The band gap widening is observed in Li-doped SnO₂ films. • All the films are ferromagnetic and the largest saturation magnetization of 7.9 emu/cm³ has been observed in Sn_0.88Mg_0.12O₂film. • The holes induced by Li replacing Sn enhance the magnetism. • The p–p interaction between the 2p states of the O atom is responsible for the long-range ferromagnetic order. - Abstract: 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 Sn_0.88Li_0.12O₂ 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