Angular and temperature dependence of the magnetic circular dichroism in 4d core-level photoemission from Gd(0001)

We present experimental and theoretical results for the angular and temperature dependence of magnetic circular dichroism in Gd 4d core-level photoelectron emission from a Gd(0001) surface in both normal and off-normal directions and with azimuthal variation. Two theoretical approaches are used to model this data: a single electron theory with full multiple scattering of the outgoing photoelectron and a full-relativistic manyelectron theory with single scattering only. Thermal effects due to atomic vibrations and the excitation of initial-state multiplets are also included. For normal emission, we find smooth free-atom-like angular variations in emission intensity, while for off-normal emission, deviations from a purely atomic model due to photoelectron diffraction effects are seen that are well predicted by photoelectron diffraction theory. We also compare dichroism measurements using two different approaches (fixed magnetization with variable light helicity and fixed light helicity with rotated sample magnetization) and find significant differences between them that are also well predicted by theory. The angular dependence of magnetic circular dichroism for a specific set of Gd 4d multiplet states has also been measured with high electron energy resolution (≤100 meV), permitting a state-specific decomposition of the dichroism. Such state-resolved dichroism is found to be very well described by our many-electron approach. Finally, we present temperature-dependent magnetic circular dichroism (MCD) data for 4d emission that should permit the study of near-surface magnetic phase transitions, and discuss the relationship of such MCD measurements to magnetization. Some future prospects and applications of such core-photoemission dichroism measurements are discussed