Enhancement of ferromagnetism and stability in Cu-doped ZnO by N2O annealing

Copper-doped ZnO (ZnO:Cu) films were prepared by the filtered cathodic vacuum arc technique at room temperature on Si substrates. The as-grown ZnO:Cu exhibited a saturated magnetic moment (M-s) of 0.36 mu(B)/Cu at room temperature. After an annealing treatment at 500 degrees C for 1 h under N2O ambient, the M-s of the ZnO:Cu increased by 100% to 0.73 mu(B)/Cu. The ferromagnetism of the annealed samples was relatively stable as compared to the as-grown sample in terms of temperature and storage time. In situ x-ray photoelectron spectroscopy of the N2O annealed sample revealed that N was incorporated into the sample. The presence of N promotes the substitution of high-spin Cu2+ ions into Zn2+ sites, which leads to the enhanced ferromagnetism in ZnO:Cu. The cyclic annealing experiments of the ZnO:Cu films in air, N2O and Zn vapor suggested that Zn interstitial defects were crucial to the N incorporation.