Well-dispersed nanoparticles with iron/iron carbide core and iron oxide shell structures may constitute an excellent magnetic material for different applications as magnetic nanofluids, contrast agents in magnetic resonance imaging, sensors and catalysts. Based on the ability of the CO2 laser pyrolysis technique to synthesize nanoparticles of the Fe/Fe2O3 core-shell type, we further improve the powder dispersion by first collecting the nanoparticles in a toluene bubbler, positioned downstream and prior to the collection filter. Structural characterisation of the samples by electron microscopy and X-ray diffraction was performed. Conditions in which clusters contain a reduced number of nanoparticles (around 50) are evidenced. Mean core-shell particle sizes of 15 nm were estimated. Finally, preliminary results on the morphology of iron/iron oxide core-shell nanoparticles as hydrocarbon-based magnetic nanofluids are presented. (c) 2007 Elsevier B.V. All rights reserved.