Nanostructured FeCo films of exceptionally high saturation magnetisation

Nanostructured FeCo films comprising small (2.1 nm mean diameter) Co nanoparticles deposited into an Fe matrix are investigated by magnetometry, transmission electron microscopy and X-ray Magnetic Circular Dichroism (XMCD). Similar films were previously reported to possess a saturation magnetisation of up to 3 µB/atom, thus exceeding the Slater-Pauling limit by a significant margin. The present work confirms the previous findings by magnetometry and demonstrates that the Co nanoparticles maintain their particulate identity within the film while adopting the crystallographic structure of the Fe matrix. The films show no evidence for voids or porosity (they exhibit the bulk density). An important factor in the high magnetisation in the films is an enhanced magnetic moment on the Co atoms, which XMCD indicates to be at least 2.21 µB, i.e., 30% larger than the bulk value for metallic cobalt.