Shapes, multiple twins and surface structures of monodisperse FePt magnetic nanocrystals

Shapes, surface atomic arrangement and structural evolution induced by annealing of monodisperse FePt nanocrystals, synthesized by a solution phase chemical procedure, have been studied by high-resolution transmission electron microscopy. The as-synthesized FePt nanocrystals display dominantly a truncated octahedron shape enclosed by flat {1 0 0}, stepped {1 1 1} and zig-zag {1 1 0} facets. The Marks decahedron FePt nanocrystals and the icosahedron based multiply twined FePt nanocrystals are identified in the as-synthesized particles. An improved structural model has been proposed for the multiply twined nanocrystals. After annealing, the {1 1 0} facets disappear and a regular cuboctahedron becomes the dominant shape. Surfaces of the FePt nanocrystals show no reconstruction but with some atomic steps and kinks.