Control of the supercrystallinity, nanocrystallinity, morphology and magnetism of cobalt nanoparticle assemblies. Towards novel colloidal crystals with high magnetic anisotropy

Starting from a colloidal solution of dodecanoic acid-coated Co nanoparticles (NP) 8.1 nm in size and low anisotropy using solvent-mediated ligand-ligand interaction strategy, we obtain either crystals or supercrystalline films. The comparison between the structural magnetic properties these two different architectures supercrystals evidences improved for crystals. This is interpreted as result both an increase mesoscopic coherence length decrease interparticle distance. In this work extend comparative study types after annealing treatment. A common batch NP used native annealed samples order to optimize accuracy comparison. complete set characterizations measurements shows that upon evolve soft hard NP, with changes constant saturation mangnetization, while supercrystal structures remain unchanged. Both characterized by smaller distance compared corresponding films, inducing higher dipolar interactions, which evidenced blocking temperature. study, highlight first fcc made hcp-Co single resulting their counterparts fcc-Co polycrystals. addition, films enhanced latter ones.