Influence of Oxidation and Size of Iron Nanoparticles on the Saturation Magnetization

Monodisperse Fe nanoparticles, with a size ranging from 4 to 10 nm, have been prepared by the thermal decomposition of Fe carbonyl. The influence of oxidation on the magnetization of Fe nanoparticles has been investigated with changing the concentration of oxygen (O₂) gas in the glove box, the oxygen atom (O) in ether and water (H₂O) in the reaction solution. When the concentration of oxygen in the glove box was more than 5000 ppm, a large decrease of the saturation magnetization (MS) was observed. There was a small decrease of MS when the O/Fe ratio was more than 10. However, in the present experimental condition, the H₂O/Fe ratio from 10^-2 to 10^-5 had little influence on the decrease of MS. MS of Fe nanoparticles was decreased with a smaller particle size. However, MS of the Fe nanoparticles with the size from 7 to 10 nm showed the size-independent behavior. Such results strongly suggested that the decrease of MS cannot be explained by these two factors of oxidization and size effect.