Nanoscale bimetallic CoxPt1-x particles dispersed in poly(vinylpyrrolidone): Synthesis from organometallic precursors and characterization

The reaction of Co(eta 3-C8H13)(eta 4-C8H12) and Pt-2(dba)(3) (dba = bis-di benzylidene acetone) under dihydrogen leads in the presence of poly(vinylpy rrolidone) to nanometric bimetallic particles CoxPt1-x. The composition of the material is determined by the initial ratio of the two organometallic p recursors. The bimetallic character of the particles is evidenced by magnet ic, structural, and spectroscopic studies. Structural changes are evidenced both by HREM and WAXS: platinum rich particles adopt a fee crystalline str ucture while cobalt rich particles adopt a non periodic polytetraedral arra ngement. The magnetic properties of the materials have been investigated. Z FC/FC measurements show that the particles are superparamagnetic and that t heir size dispersity is very low. From isothermal magnetization measurement s, the extrapolated value of the coercive field H-c (T = 0) is shown to inc rease continuously with Pt concentration, which is characteristic of bimeta llic particles.