Controlled self-assembly of colloidal cobalt nanocrystals mediated by magnetic interactions

We demonstrate the possibility of obtaining a rich set of self-assembled arrays from a single component cobalt nanocrystal (NC) system by a controlled variation of size, shape and inter-particle interactions. By selecting appropriate conditions in which one of a set of weak but competing interaction forces (steric, van der Waals, depletion, or magnetostatic) dominates we can reproducibly achieve a wide range of nanocrystal arrays. This includes hexagonal and square arrays, arrays spatially segregated by size, linear chains and lyotropic crystals exhibiting increased orientation order as a function of concentration. (C) 2003 Published by Elsevier B.V.