EELS investigation of FeCo/SiO2 nanocomposites

The factors that determine the local magnetic properties of FeCo/SiO2 nanocomposite powders and films have been analysed by electron energy-loss spectroscopy (EELS) and transmission electron microscopy (TEM). Attention has been given to the chemical composition, the local electronic structure and the atomic arrangement. The results show that the nanoparticles from sol-gel prepared powders are generally Fe-rich, whereas they are Co-rich in sol-gel prepared films. In addition, a subnanometre oxide layer at the surface of the FeCo nanoparticles has been clearly observed in the powder sample. It is found that the magnetic moment should be partly governed by alloying effects. Numerical values of the near-surface magnetic moment have been obtained using the ab-initio layer-KKR method. These values should be helpful in understanding the layer-by-layer changes of the white line ratio close to the surface of the nanoparticles.