Effect of donor doping on the magnetic properties of Co-doped ZnO films

Highly (0 0 2)-orientated Zn0.95Co0.05O and Al-doped Zn0.95Co0.05O films were prepared by using inductively coupled plasma enhanced physical vapor deposition method. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy confirmed that tetrahedrally coordinated Co2+ ions substituted for partial Zn2+ ions without changing wurtzite structure. Zn0.95Co0.05O film showed paramagnetic behavior even at 5 K while room-temperature ferromagnetism was observed in Al-doped Zn0.95Co0.05O films. It is demonstrated experimentally that the intentional donor doping plays an important role in realizing dominant ferromagnetic ordering in Co-doped ZnO films.