Nanocluster formation in Co/Fe implanted ZnO

Conversion electron Mössbauer Spectroscopy (CEMS) measurements were made on a ZnO single crystal sample implanted at room temperature (RT) with of 145 and 345 keV 59Co ions with respective fluences of 1.15×1016 ions/cm 2 and 4.17×1016 ions/cm 2, followed by implantation of 60 keV 57Fe to a fluence of 0.50×1016/cm 2 to yield a ‘box-shaped’ implantation profile with a Co + Fe concentration of about 3.2 at. %. CEM spectra were collected after annealing the sample up to 973 K. The spectra after annealing up to 973 K are similar to spectra observed in other CEMS studies on Fe implanted ZnO, but show a dramatic change after the 973 K annealing step; it is dominated by a doublet component with fit parameters typical of Fe 3+. Magnetization curves of the sample after the 973 K anneal show hysteresis, with a small residual magnetization at RT that increases at 4 K. The saturation magnetization at 4 K was approximately 0.33 μB/CoFe ion, in good agreement with observations for 5–8 nm sized Co nanoclusters in ZnO.