Nanostructural origin of the spin and orbital contribution to the magnetic moment in Fe3-xO4 magnetite nanoparticles

5 nm Fe3-xO4 nanoparticles were synthesized either by high-temperature decomposition in organic phase or in low-temperature aqueous conditions. In the first case oleic acid was covalently bonded to the nanoparticles; in the second case polyvinyl alcohol (PVA) yielded a protective coating without chemical bond. Magnetization measurements and x-ray magnetic circular dichroism showed a saturation magnetization close to bulk magnetite and an orbital moment effectively quenched in covalently bonded nanoparticles. PVA-coated nanoparticles showed a reduced value of the magnetization and similar to 3 fold increase in the orbital moment. High resolution electron microscopy suggested that this was related to the nanostructure of the samples.