Annealing-environment effects on the properties of CoPt nanoparticles formed in single-crystal Al_2O_3 by ion implantation

摘要

The ion implantation of nearly equal doses of Co and Pt into a single-crystal Al_2O_3 host followed by thermal annealing leads to the formation of nanoparticles whose phase, structure, and physical properties are strongly dependent on the annealing environment. Annealing in 96% Ar+4%H_2 gives rise to ferromagnetic, chemically ordered CoPt nanoparticles with the L1_0 structure and a magnetic coercivity that can exceed 10 kOe at 5 K. Annealing in O_2 (or in Ar) does not result in the formation of a CoPt alloy. Instead, the implanted Pt precipitates to form oriented elemental Pt nanoparticles, and the implanted Co combines with oxygen to form Co_3O_4 oxide nanoparticles. Annealing in ultrahigh-vacuum conditions results in a mixture of phases including CoPt_3 and Co_3O_4 and possibly Co. The results obtained for Co+Pi-implanted Al_2O_3 are compared with the previous results for Fe+Pt-implanted Al_2O_3 annealed in similar environments.