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 CrL_2,3 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 CrL_2,3 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/CrO ₂ 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.