The origin for increase of magnetic moment of Co in Co-doped SnO2 with oxygen vacancies

In Co-doped SnO2 fivefold degenerate Co-3d states split into five singlet states. The magnetic moment of Co is mainly contributed by the spin polarization of Co-dxy states. The introduction of oxygen vacancies largely increases the magnetic moment of Co. The increase of Co magnetic moment is caused by the conversion of spin–spin coupling between Co and its neighboring O atoms from antiparallel to parallel, which attributes to the hybridization and electrons transfer between oxygen vacancy impurity states and Co-3d states.