Regensburg 2016 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 54: Electron Theory of Magnetism and Micromagnetic Simulations
MA 54.3: Vortrag
Freitag, 11. März 2016, 10:30–10:45, H34
Influence of spin-orbit coupling on the magnetic dipole term Tz in XMCD sum rules — •Ondrej Sipr1, Hubert Ebert2, and Jan Minar2,3 — 1Institute of Physics ASCR, Prague — 2Ludwig-Maximilians-Universität, München — 3University of West Bohemia, Pilsen
Sum rules are a powerful tool for interpreting x-ray magnetic circular dichroism (XMCD) spectra: they give access to mspin and morb separately. However, these rules provide mspin only in a combination as mspin+7Tz, where Tz is the expectation value of the intra-atomic dipole operator (“magnetic dipole term”). While Tz can be usually neglected in the bulk, it can be large for surfaces, monolayers and clusters where, additionally, a considerable anisotropy of Tz is expected.
Interpretation of Tz often relies on an approximate expression for Tz valid if spin-orbit coupling (SOC) can be neglected. In that case, moreover, Tz depends on the direction of magnetization in a specific way, allowing for its elimination from XMCD experiment by doing measurements at the magic angle. Therefore, it is desirable to check whether the effect of SOC on Tz can or cannot be neglected.
We calculated Tz for Co monolayers and adatoms on noble metals (Cu, Ag, Au, Pd, Pt). We found that the effect of SOC on Tz can be neglected for monolayers but not for adatoms. Simple intuition or the magic-angle-based elimination of Tz from XMCD data thus cannot be used for adatoms or clusters which, at the same time, are systems where Tz is very important.