Marie-Claire Fromen

Synthesis and Self-Assembly of Monodisperse Indium Nanoparticles Prepared from the Organometallic Precursor [In(η5-C5H5)]

Spontaneous decomposition of [In(η5 -C5 H5 )] in the presence of poly(vinyl pyrrolidone) or trioctylphosphane oxide (TOPO) as a stabilizer gave monodisperse indium nanoparticles with a mean diameter of about 5-6 nm. In the case of TOPO, self-organization of the nanoparticles in two- and three-dimensional superlattices is observed.

Magnetic nanoparticles through organometallic synthesis: evolution of the magnetic properties from isolated nanoparticles to organised nanostructures.

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.

Structural and magnetic study of bimetallic Co1−xRhx particles

Abstract We studied the structural and magnetic properties of cobalt-rhodium nanoparticles dispersed in a polymer matrix. It is shown that the structure depends on the composition, high cobalt content leading to a non-periodic structure. Magnetic measurements confirm the dispersion, particle size, and bimetallic character of the particles. Evidence is given of enhanced magnetisation for the composition x =0.5.

Towards atomic-scale design: A theoretical investigation of magnetic nanoparticles and ultrathin films

This paper reports recent theoretical work on nanostructured materials including magnetic alloyed CoRh nanoparticles that are good candidates to combine both a large magnetic moment and a high magnetic anisotropy, and nanoscale Mn films adsorbed on W substrates as an example of artificial magnetic material. It illustrates how modern atomistic modeling and simulation can fruitfully supplement the experiments performed in the laboratory by helping to resolve and understand the experimental information, by predicting new phenomena and providing useful hints to guide the development of innovative materials with original, specifically tailored properties.

Synthesis of Cobalt Nanoparticles, Nanorods and Nanowires assisted by Oleic Acid and Oleylamine based Mixtures.

In this paper we report on the synthesis in solution of cobalt nanoparticles, nanorods and nanowires achieved through the decomposition of an organometallic precursor Co(η 3 -C 8 H 13 )(η 4 -C 8 H 12 ) and stabilized by carboxylic acid / amine based mixtures. Through decomposition of the precursor in the presence of a 1/1 mixture of oleylamine / oleic acid during 3 hours, the formation of 3 nm spherical nanoparticles is observed while hcp-cobalt nanorods are obtained if the reaction is pursued for 48 hours. Increasing the amount of oleic acid to 2 equivalents with respect to the amine results in the formation of hcp-cobalt nanowires, micrometers in length and 6 nm mean diameter‥ By using amines with various chain lengths we have observed a modification of the aspect ratio of the cobalt nanorods 1 . For example, the decomposition of Co(η 3 -C 8 H 13 )(η 4 -C 8 H 12 ) in the presence of octadecyl-, hexadecyl-, dodecyl- and octylamine in association with oleic acid allows to selectively produce nanorods of varying aspect ratio. Physical characterization using TEM and HRTEM, shows that the nanoparticles, nanorods and nanowires are all hcp single crystals. The magnetic properties reveal a saturation magnetization similar to that of bulk and a ferromagnetic behavior at room temperature for the nanorods and nanowires while the 3 nm nanoparticles remain super-paramagnetic.

Atomic Organization In Magnetic Bimetallic Nanoparticles: An Experimental And Theoretical Approach

Ultrafine bimetallic CoRh nanoparticles synthesized by a soft chemical route with compositions ranging from pure cobalt to pure rhodium are investigated using high-resolution and energy filtering transmission electron microscopy techniques as well as wide angle x-ray scattering. In parallel, they are simulated with the use of an n-body semi-empirical interaction model: quenched molecular dynamics and Monte-Carlo Metropolis simulated annealing are performed on these nanoparticles in order to find their most stable isomers as a function of composition and size. A progressive evolution from an original polytetrahedral structure to the face-centered cubic structure with increasing Rh content is observed in these particles. Strong tendency to Co surface segregation is both experimentally evidenced and confirmed by the simulations.

Size and Composition Effects in the Structure and Properties of Polymer-Protected Bimetallic Particles

We investigate the structural evolution of PtRu and CoRh ultra fine bimetallic particles as a function of their composition in the whole range of stoichiometry. Isolated particles embedded in an organic matrix are synthesized using chemical techniques in mild conditions. Their size, dispersion and structure are analyzed by HRTEM, WAXS and EXAFS techniques. The magnetic behavior of cobalt-based alloys is investigated by SQUID magnetometry. In the PtRu alloys, we demonstrate the role of composition in the structural transition from the face-centered cubic to the hexagonal close packed structure in nanoparticles and detail the mechanism of the transition. We point out the effect of size reduction and core-shell atomic distribution in the structure and the enhanced magnetization in CoRh bimetallic particles.