title: Magnetic nanoparticles through organometallic synthesis: evolution of the magnetic properties from isolated nanoparticles to organised nanostructures.
abstract: Co and NiFe nanoparticles (2.7 to 3.3 nm mean diameter) of narrow size distribution have been obtained through the decomposition of organometallic precursors in organic solutions of long alkyl chain ligands, namely oleic acid and hexadecylamine. Materials of various volume fractions were produced. The particles have been structurally characterised by WAXS. Both adopt the bulk structure: HCP in the case of cobalt; a mixture of FCC and BCC for NiFe. Their aptitude to self-assemble either on flat supports or in bulk solid state has been investigated by means of TEM and SAXS. This study suggests the crystallisation of the nanoparticles upon solvent evaporation, especially a local FCC arrangement was observed for the NiFe material. Magnetic measurements (SQUID) confirm this tendency. The blocking temperature depends on the metal volume fraction, i.e. on the anisotropy generated by the dipolar couplings (Ki). We show that, for dense samples, the particles of high intrinsic anisotropy, Ku, (Co) still display an individual behaviour while the soft ones (NiFe) display a collective behaviour.
authors.affiliation: Digital DNA Labs, Semiconductor Products Sector, Motorola, le Mirail B.P. 1029, 31023 Toulouse, France.
authors.forename: Fréderic
authors.initials: F
authors.lastname: Dumestre
authors.forename: Susana
authors.initials: S
authors.lastname: Martinez
authors.forename: David
authors.initials: D
authors.lastname: Zitoun
authors.forename: Marie-Claire
authors.initials: MC
authors.lastname: Fromen
authors.forename: Marie-José
authors.initials: MJ
authors.lastname: Casanove
authors.forename: Pierre
authors.initials: P
authors.lastname: Lecante
authors.forename: Marc
authors.initials: M
authors.lastname: Respaud
authors.forename: Arnaud
authors.initials: A
authors.lastname: Serres
authors.forename: Robert E
authors.initials: RE
authors.lastname: Benfield
authors.forename: Catherine
authors.initials: C
authors.lastname: Amiens
authors.forename: Bruno
authors.initials: B
authors.lastname: Chaudret