Dresden 2003 – wissenschaftliches Programm
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MA: Magnetismus
MA 19: Mikro- und nanostrukturierte Materialien I
MA 19.1: Vortrag
Mittwoch, 26. März 2003, 15:15–15:30, HSZ/405
The true spin moment in low-dimensional magnets obtained by angular-dependent XMCD: A critical assessment. — •Claude Ederer1, Matej Komelj2, and Manfred Fähnle1 — 1Max-Planck Institut für Metallforschung, Heisenbergstrasse 3, D-70569 Stuttgart, Germany — 2Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
In the spin sum rule used to determine the spin moment per atom from the spectrum of the x-ray magnetic circular dichroism (XMCD) there appears in addition to the true spin moment also the component Ti of the magnetic dipole operator in the direction of the magnetization. This quantity is not known in general. When it is neglected the sum rule does not yield the true spin moment. Stöhr and König (Phys. Rev. Lett. 75, 3748 (1995)) have introduced a method to eliminate the Ti term from the sum-rule analysis. The basic idea is to measure the dichroic spectra for an orientation of the magnetization in x, y, and z direction. Because for weak spin-orbit coupling the sum, Tx + Ty + Tz, is approximately zero, the true spin moment may be obtained by averaging the dichroic signal over all three directions of the magnetization. In low-dimensional systems — however — the effects of spin-orbit coupling are often very strong, and therefore the precondition, Tx + Ty + Tz ≈ 0, may be strongly violated. This is demonstrated for the case of a free-standing monatomic wire of Fe, Co, or Ni atoms by the ab initio density functional electron theory.