Post-annealing effects on structural and magnetic properties of Mn–N codoped ZnO thin films

The sputtered ZnO:Mn thin films were implanted with nitrogen ions (N+) and subsequently annealed at different temperatures up to 800 °C in N2 atmosphere. The structural and magnetic properties of the samples were systematically investigated. Both x-ray diffraction and Raman analyses reveal that all the films are of the wurtzite structure of ZnO with no distinct evidence of secondary phases. X-ray photoelectron spectroscopy studies indicate that both Mn2+ and N3− ions were incorporated into ZnO lattice successfully. While the films without nitrogen ions show paramagnetic behavior, ferromagnetism with clear hysteresis at 300 K is observed in Mn–N codoped ZnO films. Most importantly, we also found that the magnetic behavior of the codoped ZnO is very sensitive to the annealing temperature due to its effect on the activation of nitrogen ions. The strongest ferromagnetism is obtained in the films with the highest amount of nitrogen ions acceptors. Our results support the predication that the ferromagnetic ZnO:Mn2+ should be more stable of a hole-rich environment by theory.