Structural and magnetic properties of low-energy Gd implanted ZnO single crystals

We report the structural and magnetic properties of ZnO single crystals implanted with Gd ions at 40 keV. Ion beam analysis shows that after implantation up to 12% of the near-surface atoms are Gd, with most of the Gd ions occupying substitutional lattice sites. The carrier concentration of implanted films is up to several orders of magnitude larger than in unimplanted ZnO. Room temperature ferromagnetism was observed in Gd implanted and annealed ZnO. Zero-field cooled magnetisation curves reveal the presence of super-paramagnetic clusters. The annealing can cause the diffusion and/or migration of implanted ions and intrinsic defects and possibly the formation of super-paramagnetic clusters suggesting that the annealing plays a significant role towards the observed magnetic properties.