The effects of Zn vacancies on ferromagnetism in Cu-doped ZnO films controlled by oxygen pressure and Li doping

Zn_0.99Cu_0.01O films were studied both experimentally and theoretically. The films were prepared by pulsed-laser deposition on Pt(111)/Ti/SiO₂/Si substrates under various oxygen pressures to investigate the growth-dependence of ferromagnetic (FM) properties. The structural, magnetic, and optical properties were studied. It was found that all the samples possess a typical wurtzite structure, and the films exhibit room temperature ferromagnetism. The sample deposited at 600 ℃ and oxygen pressure of 10 Pa shows a large saturation magnetization of 0.83 μ_B/Cu. The enhanced FM in the (Cu, Li)-codoped ZnO is attributable to the existence of Zn vacancies (V_Zn), as shown by first-principles calculations. The photoluminescence analysis demonstrates the existence of V_Zn in both Zn_0.99Cu_0.01O and (Cu, Li)-codoped ZnO thin films, which plays an important role in the increase of ferromagnetism, according to the results of first-principles calculations.