Density-functional study on the ferromagnetism of (Mn,Na)-codoped ZnO

We have investigated the magnetic properties of (Mn,Na)-codoped ZnO, which was reported to have room-temperature ferromagnetism recently, by first-principles calculation. Our results reveal that antiferromagnetic interaction dominates in the system with Mn substitution only. The antiferromagnetism arises from the superexchange interaction between Mn atoms. When Mn and Na are codoped into ZnO, holes are introduced into the orbitals of Mn and O, which leads to strong ferromagnetism. The origin of ferromagnetism can be attributed to the hole-mediated double-exchange interaction.