Cobalt doped rings and cages of ZnO clusters: Motifs for magnetic cluster-assembled materials

First principles electronic structure studies on pure and doped ZnnOn clusters have been carried out to identify elementary motifs with potential for cluster materials. In pure clusters Zn12O12 cages are shown to be particularly stable. When doped with a single Co or Fe atom, the doped units carry a magnetic moment of 3.0 μB and 4.0 μB, respectively. Doping of Zn12O12 with two Co sites leads to ferromagnetically coupled Co moments due to direct exchange interaction. It is proposed that the assemblies of such multiple doped units may lead to semiconductors with larger doping than attainable in bulk or films.