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) indicat e 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 increas e of ferromagnetism is not owi ng to the magnetic contribution of Cu⁺ ions themselves, but owing to the enhan cement 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.