Ferromagnetic spin-order in p-type N-doped SnO_2 films prepared by thermal oxidation of SnN_x

摘要

N-doped SnO_2 films were synthesized by oxidative annealing of sputtered SnN_x films with various temperatures. The content of the residual N in SnO_2:N films decreases with the increase of temperature. N atom is incorporated well at the O lattice site and red-shifts the band-gap by the formation of impurity bands. All the films show p-type conduction and the highest hole concentration is 2.08 × 10~(19) cm~(-3) in the sample obtained at 400 ℃, indicating an effective way to alleviate the self-compensation effect by thermal oxidation. The substituted incorporation of N can also enhance the ferromagnetism and the largest saturation magnetization is 10.1 emu/cm~3. Theoretical calculations based on the density-functional theory suggest that the ferromagnetism is most likely due to the double exchange mechanism through the p-p interaction. Meanwhile, the ferromagnetic coupling competes with antiferromagnetic coupling as the N-N distance changes, causing the nonmonotonic variation of saturation magnetization.