A simple procedure to coat silica spheres with smooth layers of iron compounds is reported. It is based on the forced hydrolysis (60-85 degrees C) of iron(III) acetylacetonate solutions containing the silica cores and sodium dodecylsulfate (SDS). The role that the iron(III) precursor and SDS play in the formation of uniform coatings is discussed. The thermal evolution of the composites up to the crystallization of the initially amorphous coating was also studied. Finally, the core-shell particles, as prepared, were thermally reduced under hydrogen atmosphere to produce magnetic composites whose magnetic properties were also evaluated as a function of the reduction temperature. (c) 2005 Elsevier Inc. All rights reserved.