Enhancement of magnetism of Zn0.95Co0.05O films by p-type Cu+ doping

Zn0.95Co0.05O and Zn0.91Co0.05Cu0.04O thin films were fabricated on Si (111) substrate by the reactive magnetron sputtering method at different O-Ar ratios. Detailed characterizations by X-ray diffractometry (XRD), X-ray photo-electronic spectrum (XPS), and electron paramagnetic resonance (EPR) indicate that the doped Cu ions substitute the Zn2+ ions in the ZnO lattice. The doped Cu ions are in Cu+ and Cu2+ mixture valence states. The ferromagnetism of the Zn0.91Co0.05Cu0.04O film increases gradually the increasing Cu+ ions concentration. The results indicate that the increase of ferromagnetism is not owing to the magnetic contribution of Cu+ ions themselves, but owing to the enhancement of magnetic interaction between Co ions, which suggests that p-type doping of Cu+ ions plays an important role in mediating the ferromagnetic coupling between Co ions.