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 300–800K with dilute, radioactive Mn+57 ions, decaying to the Fe57m Mössbauer state, we show that, most likely, Fe atoms, located on Zn sites in a high-spin Fe3+ state at ⩽600K with large magnetic moments, are in a magnetically ordered atomic surrounding with ordering temperatures ⪢600K. 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.

Doping of the nanocrystalline semiconductor ZnO with the donor In111 was achieved by the incorporation of In111 atoms during the growth process followed by a hydrothermal treatment at 473 K. The incorporation of In111 on substitutional Zn sites was shown by the perturbed γγ angular correlation technique. The structural quality of nanocrystalline ZnO with a mean grain size of 11 nm is significantly improved by annealing at 473 K, as revealed by x-ray diffraction, transmission electron microscopy, optical absorption measurements, and photoluminescence spectroscopy. It is shown that the incorporation of In111 on undisturbed Zn sites in nanocrystalline ZnO seems to be supported by the onset of crystal growth and by the removal of intrinsic defects.

The group Ib impurities Cu and Ag on substitutional Zn sites are among possible candidates for p-type doping of ZnO. In order to explore possible lattice sites of Cu and Ag in ZnO the radioactive impurities 67 Cu and 111 Ag were implanted at doses of 4×10 12 cm −2 to 1×10 14 cm −2 at 60 keV into ZnO single crystals. The emission channeling effects of β − particles from the decay were studied by means of position-sensitive electron detectors, giving direct evidence that in the asimplanted state large fractions of Cu and Ag atoms (60-70% for Cu and 30% for Ag) occupy almost ideal substitutional Zn sites with root mean square (rms) displacements of 0.014-0.017 nm. However, following vacuum annealing at 600°C and above both Cu and Ag were found to be located increasingly on sites that are characterized by large rms displacements (0.03-0.05 nm) from Zn sites. We conclude that in high-temperature treated ZnO Cu and Ag are most likely not simply replacing Zn atoms but are incorporated in complexes with other crystal defects or as clusters.