Structure and chemical order in

The 300\un{K} structure of soft chemistry synthesized \chem{Co_{\it x} Rh_{1-{\it x}}} ($x = 0.25$, 0.50, 0.75) particles, 1.7 to 2.5\un{nm} large, has been determined by atomic-scale simulations using an interaction model fitted on both ab initio and experimental results. All the measured structural features, strongly different from the ones in the corresponding bulk alloys, have been consistently reproduced. Two major effects, i.e. a strong Co surface segregation and an expansion of the mean bond length, are demonstrated and both are consistent with the drastic enhancement of the magnetization observed in these clusters. Interestingly, the method also provides new insights into interpretation of the experimental results

Synthesis and magnetic properties of nanoscale bimetallic Co 1 Rh 1 particles

International audienc

Synthesis and Magnetism of Co x Rh 1 - x and Co x Ru 1 - x Nanoparticles

International audienc

Structural study of bimetallic CoxRh1−xCo_xRh_{1-x} nanoparticles: Size and composition effects

The structure of ultrafine bimetallic CoxRh1?x nanoparticles synthesized in mild conditions by codecomposition of organometallic precursors in the presence of a polymer or a ligand has been studied using high-resolution electron microscopy and wide-angle x-ray scattering techniques. While pure rhodium particles exhibit the main structural features of a face centered cubic (fcc), alloying with cobalt induces a progressive loss of periodicities, leading in high-cobalt-content particles to a polytetrahedral structure close to the one already encountered in pure-cobalt particles. When increasing the synthesis temperature, the polytetrahedral structure remains remarkably stable, while particles with higher rhodium content clearly evolve towards perfect fcc. Increasing the size of the particles up to 5–6nm stabilizes the structural phases encountered in the phase diagram of the bulk alloy. Different element-sensitive techniques, x-ray absorption spectroscopy (XANES and EXAFS) and energy-filtering transmission electron microscopy, have also been implemented in order to get chemical information. Evidence is given for a cobalt surface segregation in these bimetallic particles, highly favorable for magnetic-moment enhancement