title: Beyond entropy: magnetic forces induce formation of quasicrystalline structure in binary nanocrystal superlattices.
abstract: Here, it is shown that binary superlattices of Co/Ag nanocrystals with the same size, surface coating, differing by their type of crystallinity are governed by Co-Co magnetic interactions. By using 9 nm amorphous-phase Co nanocrystals and 4 nm polycrystalline Ag nanocrystals at 25 °C, triangle-shaped NaCl-type binary nanocrystal superlattices are produced driven by the entropic force, maximizing the packing density. By contrast, using ferromagnetic 9 nm single domain (hcp) Co nanocrystals instead of amorphous-phase Co, dodecagonal quasicrystalline order is obtained, together with less-packed phases such as the CoAg13 (NaZn13-type), CoAg (AuCu-type), and CoAg3 (AuCu3-type) structures. On increasing temperature to 65 °C, 9 nm hcp Co nanocrystals become superparamagnetic, and the system yields the CoAg3 (AuCu3-type) and CoAg2 (AlB2-type) structures, as observed with 9 nm amorphous Co nanocrystals. Furthermore, by decreasing the Co nanocrystal size from 9 to 7 nm, stable AlB2-type binary nanocrystal superlattices are produced, which remain independent of the crystallinity of Co nanocrystals with the superparamagnetic state.
authors.affiliation: †Sorbonne Universités, UPMC Univ Paris 06, UMR 8233, MONARIS, F-75005, Paris, France.|‡CNRS, UMR 8233, MONARIS, F-75005, Paris, France.
authors.forename: Zhijie
authors.initials: Z
authors.lastname: Yang
authors.affiliation: †Sorbonne Universités, UPMC Univ Paris 06, UMR 8233, MONARIS, F-75005, Paris, France.|‡CNRS, UMR 8233, MONARIS, F-75005, Paris, France.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Wei
authors.affiliation: §CEA/IRAMIS, CEA Saclay, 91191, Gif-sur-Yvette, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Bonville
authors.affiliation: †Sorbonne Universités, UPMC Univ Paris 06, UMR 8233, MONARIS, F-75005, Paris, France.|‡CNRS, UMR 8233, MONARIS, F-75005, Paris, France.|§CEA/IRAMIS, CEA Saclay, 91191, Gif-sur-Yvette, France.
authors.forename: Marie-Paule
authors.initials: MP
authors.lastname: Pileni