Multi-roles of Cu ions in the ferromagnetic properties of (Cu, Al)-codoped ZnO thin films

(Cu, Al)-codoped ZnO films have been prepared by inductively coupled plasma enhanced physical vapor deposition (ICP-PVD) system at different substrate temperatures ranging from room temperature to 527 °C. The electrical and magnetic properties, defect and chemical valence state were studied. Room-temperature ferromagnetism was observed in all of the (Cu, Al)-codoped ZnO films. It was found that Cu ions played an important role in the ferromagnetism origin and showed multiple roles in the semi-insulating and conductive regimes according to the Hall effect measurements. For the semi-insulating regime, Cu ions showed mixed valence states of +1/+2 and acted as local charge reservoirs. For the conductive regime, Cu ions showed dominant valence states of +2 and acted as magnetic ions.

► (Cu, Al)-codoped ZnO thin films have been prepared by ICP-PVD method.
► Room-temperature ferromagnetism was observed in all the as-grown samples.
► The effect of Cu-doping in inducing ferromagnetism of (Cu, Al)-codoped ZnO thin films was studied.
► Cu ions played multiple roles in the semi-insulating and conductive (Cu, Al)-codoped ZnO thin films.