On the importance of the magnetic dipole term T z in analyzing X-ray magnetic circular dichroism spectra of clusters

Employing ab initio relativistic impurity Green function calculations to Fe and Co clusters on Ni and Au surfaces, we assess the usability of the X-ray magnetic circular dichroism (XMCD) spin sum rule for studying magnetism of supported transition metal clusters. We demonstrate that neglect of the magnetic dipole term T z might lead to a completely false estimate of how the spin magnetic moment μ spin depends on the cluster size. In particular, this would be the case of Co N clusters on Au(111) and on Pt(111).