Origin of ferromagnetism of (Co,Al)-codoped ZnO from first-principles calculations

Magnetic mechanisms for the (Co,Al)-codoped ZnO, based on the first-principles calculations, are evaluated. Additional electrons induced by Al doping can stabilize the ferromagnetic state in Co-doped ZnO. The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction may be the dominant mechanism when the distance between Co and Al is far away, while the double-exchange interaction may gain an advantage over the RKKY when the distance is near. The multiple mechanisms can explain the relationship between the magnetic performance and the relative substitutional site of Al. The study yields insight into the origin of the ferromagnetism of ZnO-based materials.