Defect-induced ferromagnetism in insulating Mn–P codoped ZnO grown in oxygen-rich environment

Zn0.93Mn0.05P0.02O films have been prepared on quartz substrates by pulsed laser deposition (PLD). The ferromagnetic film obtained in oxygen-rich (40 Pa) environment is not carrier mediated, but coexists with dielectric state. The Mn ions are located at the substitutional Zn sites as revealed by the Mn K-edge XAFS spectroscopy. The Raman analysis indicated the existence of numerous vacancies, which is attributed primarily to PZn–2VZn complex defects. This is experimentally confirmed by quenched ferromagnetism after annealing at 600 °C in O2, due to break down of the PZn–2VZn complex. In contrast, all the Zn0.93Mn0.05P0.02O films grown at lower (0.04–4 Pa) oxygen pressures (PO2) with and without post-annealing exhibited n-type conduction with paramagnetism. The results are consistent with the bound magnetic polaron (BMP) model, in which localized PZn–2VZn complex defects in the insulating film mediated the ferromagnetic ordering.