Cobalt nanocrystals with very low size distribution self-assemble to produce well-grown face-centered cubic (fcc) "supra" crystals. By adjusting the substrate temperature during the solvent evaporation process, structural ordering is controlled. Hence, it is possible to obtain either a long-range arrangement of the magnetic nanocrystals or a short-range ordering. The film morphology can be improved in terms of homogeneity and crack density by lowering the evaporation rate of the solvent. The ordering of the nanocrystals into a "supra" crystal is accompanied by a slight change of the magnetic properties.