Defects enhanced ferromagnetism in Cu-doped ZnO thin films

We present here new evidences of point defects enhanced ferromagnetism in Cu-doped ZnO thin films by different characterization methods. Cu-doped ZnO thin films with Cu concentrations ranging from 0.05 to 5 at.% were prepared by an inductively coupled plasma enhanced physical vapor deposition system. Room-temperature ferromagnetism is observed in all the films. The saturation magnetization shows an increasing trend with the increase of Cu concentration except a slight decrease for the 1 at.% Cu-doping. Further study performed by Raman spectra, X-ray absorption spectra and extended X-ray absorption fine structure indicate the existence of Cu2+ ions and point defects in all the films. The local structural characterization and magnetic properties reveal that the sample with larger saturation magnetization has a higher concentration of point defects.