Theoretical Fe L_2,3- and K-edge x-ray magnetic circular dichroism spectra of free iron clusters

A fully relativistic ab initio theoretical scheme is employed for investigating L_2,3- and K-edge x-ray absorption near-edge structure (XANES) and x-ray magnetic circular dichroism (XMCD) spectra of free Fe clusters of 9–89 atoms. The L_2,3-edge spectra of clusters differ from spectra of bulk only quantitatively; a higher degree of localization of the d electrons in clusters is reflected through a higher intensity of the main XANES and XMCD peaks at the absorption edge. The K-edge XANES and XMCD spectra of clusters, on the other hand, differ from their bulk counterparts more significantly, even for the largest clusters investigated within our study. Several features, which could serve as spectroscopic markers of the difference between the clusters and bulk, were identified in both the L_2,3- and K-edge spectra. Contracting the bond lengths in clusters changes XMCD spectra only quantitatively.