Sum rule distortions in fluorescence-yield x-ray magnetic circular dichroism

Abstract

The quantitative analysis of $3d$ transition metal ${\mathrm{L}}_{2,3}$ edge x-ray magnetic circular dichroism (XMCD) spectra and the related sum rules are compared for measurements with electron yield and fluorescence yield detection. Multiplet calculations on divalent ions show that fluorescence yield detected sum rule derived expectation values of ${\mathrm{L}}_{z}$ and ${\mathrm{S}}_{z}$ show noticeable deviations and detection angle dependence. We show that small deviations of the polarization dependent fluorescent decay values lead to significant deviations in the ${\mathrm{L}}_{z}$ and ${\mathrm{S}}_{z}$ sum rule values. Fe and Co experimental XMCD spectra of a supported 10 nm ${\mathrm{CoFe}}_{2}{\mathrm{O}}_{4}$ thin film are measured simultaneously by both electron and fluorescence yield. The deviations shown in the experimental data are well explained by the calculations and are shown to mainly depend on the polarization dependent total decay. We conclude that fluorescence yield detected x-ray magnetic circular dichroism is unsuitable for quantitative analysis of the ${\mathrm{L}}_{z}$ and ${\mathrm{S}}_{z}$ sum rule values.