Size dependence of the magnetic moments of exposed nanoscale iron particles

The magnetic moments in exposed, mass-selected, nanoscale Fe clusters in the size range 1.89–2.20 nm (300–475 atoms), deposited onto graphic in situ have been measured by X-ray magnetic circular dichroism. The smallest clusters possess moments that are enhanced by around 4% for m spin and 80% for m orb and decrease towards the bulk value with increasing size. The larger clusters show an in-plane anisotropy that is consistent with the anisotropy in the orbital moment. The smallest clusters are, within experimental error, magnetically isotropic. The anisotropy constant in the 475-atom clusters is significantly higher than the bulk value.