Annealing-environment effects on the properties of CoPt nanoparticles formed in single-crystal Al 2 O 3 by ion implantation

• Published in: Journal of applied physics 2005-12, Vol.98 (11), p.114311-114311-7
• Main Authors: White, C. W., Withrow, S. P., Budai, J. D., Thomas, D. K., Williams, J. M., Meldrum, A., Sorge, K. D., Thompson, J. R., Ownby, G. W., Wendelken, J. F., Boatner, L. A.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.2138801

The ion implantation of nearly equal doses of Co and Pt into a single-crystal Al 2 O 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 L 1 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 3 O 4 oxide nanoparticles. Annealing in ultrahigh-vacuum conditions results in a mixture of phases including Co Pt 3 and Co 3 O 4 and possibly Co. The results obtained for Co + Pt -implanted Al 2 O 3 are compared with the previous results for Fe + Pt -implanted Al 2 O 3 annealed in similar environments.