Role of intrinsic defects in ferromagnetism of SnO2: First-principles calculations

The effects of tin interstitial (Sn), oxygen vacancy (Vo) and Sn-i + V-O defect pair on the electronic structure and magnetic properties of undoped SnO2 are investigated by means of density functional calculations. Only single positively charged O vacancies V-O(1+) can induce local magnetic moments in bulk SnO2. The magnetic coupling between two V-O(1+) calculated by generalized gradient approximation (GGA) is ferromagnetic. Self-consistent bandgap correction, which is achieved by adding a Coulomb U on O-2s orbital, results in the full occupation of the spin up gap state of V-O(1+). Consequently, the magnetic coupling calculated by GGA - U-S becomes anti-ferromagnetic, which shows that a self consistent bandgap correction is essential for the correct description of the magnetism in widegap SnO2. The results indicate that O vacancy in bulk SnO2 cannot induce ferromagnetism which suggests that the atoms or defects located at the surface or substrate interface may play a key role in turning the ferromagnetism observed in undoped SnO2. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim