Strong Final State Effects in L_2,3 XMCD of Ionic Rare Earth Materials

Abstract
The La XMCD spectra of rare earth insulating systems show line shapes that look like a derivative of the nearedge XAS spectra. This line shape is shown to be due to intra-atomic final state Coulomb interactions between the 2p → 5d excited photoelectron and the magnetically aligned 4f shell. An atomic multiplet calculation starting from a 4f^N5d⁰ initial state gives good agreement with the observed line shapes. The experimental fact that the temperature dependence of the XMCD follows that of the 4f moment supports such a local description. Furthermore, an analysis in terms of spectral moments based on the 5d⁰ assumption yields sum rules for the first moments of the edges that explain the trends in literature data for metallic systems.