Mesoscopic Structures of Nanocrystals: Collective Magnetic Properties Due to the Alignment of Nanocrystals

Abstract

Maghemite nanocrystals, deposited by slow evaporation on HOPG (highly oriented pyrolytic graphite) substrate, form mesoscopic structures which strongly depend on the nanocrystal coating. When the coating consists of citrate ions and octanoic acid, tubelike structures are formed when the deposition process takes place under an applied magnetic field. Conversely, dense films are formed when the nanocrystals are coated with propanoic acid and dodecanoic acid. The magnetic behaviors markedly differ with the organization of nanocrystals and are attributed to the change in the anisotropy of the organized structures. Nanocrystals organized in tubes behave as nanowires.