Impact of the magnetic dipole term Tz on x-ray magnetic circular dichroism spectra of low-dimensional systems

*Ondřej Šipr (1), Hubert Ebert (2), Ján Minár (3)
(1) Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic, (2) Ludwig-Maximilians-Universitat, Munich, Germany, (3) University of West Bohemia, Pilsen, Czech Republic

Magnetism of diluted low-dimensional systems and nanostructures is often studied by means of x-ray magnetic circular dichroism (XMCD). The analysis of XMCD experiments is greatly aided by the XMCD sum rules which, in principle, give access to the spin and orbital magnetic moments of the chemically specific photoabsorbing atom. Unfortunately, the XMCD spin sum rule allows for the spin magnetic moment mspin to be determined only in combination with the magnetic dipole term Tz. This Tz term is not just a minor factor that affects the sum rules analysis; on the contrary, it may change the overall picture completely. We present few examples demonstrating that neglecting the Tz term could in some cases lead to completely wrong conclusions about the trends of mspin with the size of the system or with the direction of the magnetization.

Earlier it was shown that the magnetic dipole term Tz can be eliminated from the sum rule analysis altogether by employing a special experimental setup. We demonstrate that for supported nanostructures this can be done only if certain conditions concerning the strength of the spin-orbit coupling and the hybridization between the states of the nanostructure and of the substrate are satisfied.