First-principles investigations of Co- and Fe-doped SnO2

We have investigated the electronic and magnetic properties of Co- and Fe-doped SnO2 by first-principles methods. The obtained results show that the ferromagnetic order is energetically much favored relative to the antiferromagnetic order in all the considered models of Co- and Fe-doped SnO2. The exchange interaction between Co ions is a long-range ferromagnetic interaction and gradually weakened as the distance between Co ions increases. For Fe-doped SnO2, the exchange interaction is also a long-range ferromagnetic one, but it oscillates with the variation of the distances between Fe ions. In addition, we further probe the concentration effect on the magnetic properties in the doped systems. The obtained results show that the exchange interaction between Co and Fe ions is reduced, implying that the enhancement of Curie temperature is not favored by increasing Co- and Fe-doping concentrations.