Superparamagnetic iron oxide nanoparticles are of interest for use as magnetic resonance imaging contrast agents and in thermal therapies. Silica nanoparticle coatings can increase the thermal stability of particles and provide a biologically inert surface for the attachment of functionalizing ligands. In this study, silica-coated magnetic iron oxide nanoparticles were produced by synthesizing core iron oxide nanoparticles in a thermal plasma followed by coating the particles with silica by photoinduced chemical vapor deposition (photo-CVD). Core particles were shown to be superparamagnetic with a maximum saturation magnetization of 29 emu/g. The photo-CVD process produced silica coatings with thicknesses up to 6 nm. Coatings were found to consist of conformal high-purity silica. The presence of the coating was found to decrease the saturation magnetization when evaluated on a total mass basis (iron oxide and silica).