The effects of tin interstitial (Sni), oxygen vacancy (VO), and Sni + VO defect pair on the electronic structure and magnetic properties of undoped SnO2 were investigated by means of density functional calculations. Only single positively charged O vacancies VO+ could induce local magnetic moments in bulk SnO2. The magnetic coupling between two VO+ calculated by generalized gradient approximation was ferromagnetic. Self-consistent band-gap correction, which was achieved by adding a Coulomb U on O-2s orbital, resulted in the full occupation of the spin-up gap state of VO+. Consequently, the magnetic coupling calculated by generalized gradient approximation  + US became antiferromagnetic, which showed that a self-consistent band-gap correction was essential for the correct description of the magnetism in wide-gap SnO2. The results indicated that O vacancy in bulk SnO2 could not induce ferromagnetism, which suggested that the atoms or defects located at the surface or substrate interface might play a key role in turning the ferromagnetism observed in undoped SnO2.

Role of Intrinsic Defects in Ferromagnetism of SnO2: First-Principles Calculations. H.Wang, Y.Yan, K.Li, X.Du, Z.Lan, H.Jin: Physica Status Solidi B, 2010, 247[2], 444–8