Structural, magnetic, and optical properties of Co- and Gd-implanted ZnO(0001) substrates

ZnO(0001) substrates were ion implanted with 100 keV of Co and 300 keV of Gd at different fluences ranging from 5 x 10(13)-1 x 10(15)/cm(2). The resulting Co: ZnO and Gd: ZnO samples were analyzed with respect to their structural, magnetic, and optical properties. The effect of annealing at 350 degrees C on the structure and the resulting magnetic and optical properties were investigated as well. For Co:ZnO hardly any changes were observable, neither in the structural nor in the magnetic properties, even though the existence of substitutional Co2+ in the ZnO lattice could be shown by means of low temperature photoluminescence especially for Zn-annealed samples. For the much larger Gd ion the implantation leads to a changed crystal structure, which leads to a ferromagneticlike behavior for higher implantation doses, which could even be enhanced by annealing in vacuum. Ferromagnetic behavior in annealed Gd: ZnO is corroborated by ferromagnetic resonance measurements at low temperatures. The distinct behavior of Gd- and Co-implanted ZnO highlights the importance of defects in the understanding of the magnetic properties in dilute magnetic semiconductors. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3000452]