Konstantin Hirsch (Special Seminar)

Date(s) - Apr 7 2014
2:00 PM - 3:00 PM

Shasta Room 361, Building 40, SLAC


Insights into magnetism on the atomic scale from x-ray spectroscopy on size-selected free clusters

Konstantin Hirsch


Helmholtz-Zentrum, Berlin, Germany

We apply x-ray absorption and x-ray magnetic circular dichroism (XMCD) spectroscopy to gas phase clusters to probe the intrinsic magnetic properties of size-selected clusters that are free from any substrate interaction. Employing these techniques to pure transition metal clusters enables us to study a variety of phenomena ranging from intra-cluster spin coupling in  molecular clusters as discussed for the Cr2+ and Mn2+
dimer to the size-dependent quenching of the orbital moment in Fen+ clusters. We exploit the element-specificity of x-ray absorption spectroscopy that allows us to investigate the local electronic and magnetic properties of a single impurity embedded in a finite host. In my talk, I will address the question of how a single magnetic impurity interacts with a finite host material using two exemplary systems: In manganese-doped silicon clusters we find, in combination with density functional theory calculations, a strong correlation of the size of the impurity’s spin magnetic moment and structural motifs of the clusters. These findings can be generalized to extended systems explaining the variety of manganese impurity spin moments observed in bulk silicon. Secondly, we apply XMCD spectroscopy to chromium-doped gold clusters to explore the limits of the well established Anderson impurity model in the finite size regime. We adopt a tight binding model Hamiltonian to the problem and suggest a possibility to stabilize or even restore the impurity’s spin magnetic moment by introducing an energy gap in the host density of states.