Observation of dynamical spin-dependent electron interactions and screening in magnetic transitions via core-level multiplet-energy separations

► Gd 5s and 4s multiplet splittings of Gd(0001) change during magnetic transitions. ►·Atomic multiplet theory and LDA+U calculations partially explain these results. ►·Provide a novel probe of dynamical spin-dependent screening/magnetic fluctuations. ► Suggest future experiments in a time-resolved mode, e.g. using free electron lasers. The magnetic phase transitions for Gd(0001) grown on W(110) – a bulk transition at 293K and a surface transition about 85K above this – are found to influence the energy separation of the Gd 5s and 4s core-photoelectron doublets. The 5s doublet separation ΔE5s changes over a range of temperatures spanning these transitions, and decreases by a maximum of 60meV in this region, but then recovers its original value; the 4s doublet shows a smaller change in the reverse direction, which does not recover at high temperature. Some of these effects are semi-quantitatively understood from free-atom multiplet theory and from theoretical calculations based on all-electron LDA+U calculations including 4f electron correlation effects. However, the high-temperature behavior of the data also suggest a dynamical nature to these effects via spin-dependent electron screening that is influenced by magnetic fluctuations. Several avenues for studying such effects in a time-resolved manner in future experiments are discussed.