FePt nanoparticle hydrodynamic size and densities from the polyol process as determined by analytical ultracentrifugation

We have studied particle size distributions of FePt nanoparticles with analytical ultracentrifugation. The particles were made with the common polyol process by thermal decomposition of iron pentacarbonyl and reduction of platinum (11) acetylacetonate. The size distribution is found to be bimodal (dual) rather than a monomodal distribution as normally reported. The density values for these particles indicates that the smaller particles, similar to 7.4 nm diameter, have a density above 4 g cm(-3) while the larger particles, similar to 16 nm, have a density of similar to 3.2 g cm(-3) due to a higher Fe content in the lighter particles.