Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors argue that the observed ferromagnetism stems from ferromagnetic precipitates or spinodal decomposition rather than from carrier mediated magnetic impurities, as required for a diluted magnetic semiconductor. In the present paper we answer this question for Fe-implanted ZnO single crystals comprehensively. Different implantation fluences and temperatures and post-implantation annealing temperatures have been chosen in order to evaluate the structural and magnetic properties over a wide range of parameters. Three different regimes with respect to the Fe concentration and the process temperature are found: 1) Disperse Fe2+ and Fe3+ at low Fe concentrations and low processing temperatures, 2) FeZn2O4 at very high processing temperatures and 3) an intermediate regime with a co-existence of metallic Fe (Fe0) and ionic Fe (Fe2+ and Fe3+). Ferromagnetism is only observed in the latter two cases, where inverted ZnFe2O4 and α-Fe nanocrystals are the origin of the observed ferromagnetic behavior, respectively. The ionic Fe in the last case could contribute to a carrier mediated coupling. However, their separation is too large to couple ferromagnetically due to the lack of p-type carrier. For comparison investigations of Fe-implanted epitaxial ZnO thin films are presented.
@article{arxiv.0908.0405,
title = {Fe-implanted ZnO: Magnetic precipitates versus dilution},
author = {Shengqiang Zhou and K. Potzger and G. Talut and H. Reuther and J. von Borany and R. Groetzschel and W. Skorupa and M. Helm and J. Fassbender and N. Volbers and M. Lorenz and T. Herrmannsdoerfer},
journal= {arXiv preprint arXiv:0908.0405},
year = {2009}
}