Defect-related local magnetism at dilute Fe atoms in ion-implanted ZnO

Semiconductors, which are ferromagnetic at room temperature (RTFM), are strived after as potential multifunctional materials. For ZnO, RTFM has been achieved by heavy doping with 3d transition metals. However, neither the conditions for nor the origin of the magnetism is as yet understood. Here, by implanting ZnO at temperatures of 300-800 K with dilute, radioactive Mn-57(+) ions, decaying to the Fe-57m Mossbauer state, we show that, most likely, Fe atoms, located on Zn sites in a high-spin Fe3+ state at <= 600 K with large magnetic moments, are in a magnetically ordered atomic surrounding with ordering temperatures >> 600 K. The formation/annealing of the ordering is proposed to occur/disappear on an atomic scale upon the association/dissociation of complexes of Mn/Fe probe atoms with the (mobile) Zn vacancies that are created in the implantation process. These results challenge present concepts to model (ferro)magnetic ordering in 3d-metal doped oxides and suggest this role of vacancies in the magnetism to be a rather general phenomenon. (c) 2007 American Institute of Physics.