Design of ferromagnetism in Cu-doped ZnO nanowires: First-principles prediction

Abstract

We performed first-principles calculations to study the electronic and magnetic properties of Cu-doped ZnO nanowires. It is found that the isolated Cu dopant is spin polarized with a magnetic moment of 0.56μB and prefers to substitute for the outermost surface Zn site in ZnO NW. At a higher doping concentration, the analysis of formation energy shows that two Cu atoms are most stable when they are near to each other in the surface Zn sites. Irrespective of the sites that Cu dopants occupy, Cu atoms in ZnO NWs are always ferromagnetically coupled to each other via the mediating oxygen atoms. Furthermore, robust ferromagnetism is not sensitive to surface passivation with hydrogen. The ferromagnetic coupling in Cu-doped ZnO NWs can be attributed to the hole-mediated double exchange through the strong p-d indirect interaction between Cu and the neighboring oxygen.