  Unwanted secondary phases are one of the major problems in diluted magnetic
semiconductor creation. Here, the authors show possibilities to avoid such
phases in Fe implanted and postannealed ZnO(0001) single crystals. While -Fe
nanoparticles are formed after such doping in as-polished crystals, high
temperature (1273 K) annealing in O2 or high vacuum before implantation
suppresses these phases. Thus, the residual saturation magnetization in the
preannealed ZnO single crystals is about 20 times lower than for the
as-polished ones and assigned to indirect coupling between isolated Fe ions
rather than to clusters.
