The electronic structure and ferromagnetic stability of Co-doped SnO2 were studied

using the first-principle density functional method within the generalized gradient approximation (GGA) and GGA+U schemes. The addition of effective UCo

transforms the ground state of Co-doped SnO2 to insulating from half-metallic and

the coupling between the nearest neighbour Co spins to weak antimagnetic from

strong ferromagnetic. GGA+UCo calculations showed that the pure substitutional

Co defects in SnO2 could not induce the ferromagnetism. Oxygen vacancies tend to

locate near Co atoms. Their presence increases the magnetic moment of Co and

induces the ferromagnetic coupling between two Co spins with large Co–Co

distance. The calculated density of state and spin density distribution calculated by

GGA+UCo showed that the long-range ferromagnetic coupling between two Co

spins was mediated by spin-split impurity band induced by oxygen vacancies.

More charge transfer from impurity to Co-3d states and larger spin split of Co-3d

and impurity states induced by the addition of UCo enhance the ferromagnetic

stability of the system with oxygen vacancies. By applying a Coulomb UO on O 2s

orbital, the band gap was corrected for all calculations and the conclusions derived

from GGA+UCo calculations were not changed by the correction of band gap.

The Role of Co Impurities and Oxygen Vacancies in the Ferromagnetism of Co-

Doped SnO2: GGA and GGA+U Studies. H.Wang, Y.Yan, Y.S.Mohammed, X.Du,

K.Li, H.Jin: Journal of Magnetism and Magnetic Materials, 2009, 321[19], 3114-9