Synthesis, self-assembly, and magnetic behavior of a two-dimensional superlattice of single-crystal «-Co nanoparticles

A method of producing high-quality magnetic colloidal dispersions by the rapid pyrolysis of cobalt carbonyl in an inert atmosphere was employed to produce monodispersed, stabilized, defect-free «-cobalt nanocrystals, with spherical shapes and sizes ranging from 3 to 17 nm. The size distribution and the shape of the nanocrystals were controlled by varying the surfactant ~oleic acid, phosphonic oxides and acids, etc.!, its concentration, and the reaction temperature. These particles have been observed to produce two-dimensional self-assemblies when evaporated at low rates in a controlled atmosphere. A collective behavior due to dipolar interactions has been observed in the low susceptibility measurements corresponding to a highly ordered fine particles system. © 2001 American Institute of Physics. @DOI: 10.1063/1.1362333#