X-ray magnetic circular dichroism strongly influenced by non-magnetic cover layers

Total electron yield (TEY) is the dominating measurement mode in soft X-ray absorption spectroscopy (XAS), where the sampling depth is generally assumed to be quite small and constant, and the related self-absorption or saturation phenomena are about to be negligible at normal incidence conditions. From the OK edge to CrL2,3 edge XAS ratio we determined a strong change in the effective electron escape length between an uncovered and a RuO2 covered CrO2 sample. This effect has been explained by a simple electron energy filtering model, providing a semi quantitative description. In addition, this simple model can quantitatively describe the unexpected reduced and positive CrL2,3 X-ray magnetic circular dichroism (XMCD) signal of a RuO2/CrO2 bilayer, while previous results have identified a clear negative Cr magnetization at the RuO2/CrO2 interface. In our case this escape length enhancement has strong impact on the XMCD sum rule results and in general it provides much deeper sampling depth, but also larger self-absorption or saturation effects.