Room temperature ferromagnetism in Mn-doped ZnO films mediated by acceptor defects

Mn-doped ZnO films with preferred c-axis growth orientation were prepared by pulsed laser deposition under N2 atmosphere on a-plane sapphire substrates. Large positive magnetoresistance amounting to 60% was observed at 5 K. Clear anomalous Hall effect was observed at 20 K. Ferromagnetism with Curie temperature higher than 290 K has been observed, and a deep acceptor trap due to Zn vacancies with a thermal activation energy amounting to 0.815 eV has been detected by deep-level transient spectroscopy. For comparison, only paramagnetism was observed in Mn-doped ZnO films with donor traps prepared under O2 atmosphere. Their results clearly demonstrate that the ferromagnetism in Mn-doped ZnO originates from the parallel alignment of magnetic moments mediated by acceptor defects.