Influence of the oxidative annealing temperature on the magnetism of (Mn, N)-codoped ZnO thin films

(Mn, N)-codoped ZnO films have been achieved by oxidative annealing of sputtered Zn2N3:Mn films at different temperatures in flowing O2 ambient. X-ray diffraction measurements and x-ray photoelectron spectroscopy studies indicate that both divalent Mn2+ and trivalent N3− ions are incorporated into ZnO lattice. Ferromagnetism with Curie temperature above 300 K was observed in the (Mn, N)-codoped ZnO films and found to be sensitive to the oxidative annealing temperature due to its strong effect on the carrier type and concentration. The strongest ferromagnetism has been found in the (Mn, N)-codoped ZnO films with the highest hole concentration in this study. The results indicate that holes are favorable for ferromagnetic ordering of doped Mn2+ ions in ZnO in agreement with the recent theoretical studies. The mechanism of ferromagnetic coupling in (Mn, N)-codoped ZnO is discussed.