Fe 2p absorption in magnetic oxides: Quantifying angular-dependent saturation effects

Abstract

We show that the absorption spectra of magnetic iron oxides $({\mathrm{Fe}}_{3}{\mathrm{O}}_{4}, \ensuremath{\alpha}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3})$ exhibit strong angular-dependent saturation effects when measured in the total electron yield mode. We analyze quantitatively the impact of saturation by independent evaluations of the probing depth (d), the absorption length (\ensuremath{\lambda}), and their ratio $(\ensuremath{\lambda}/d).$ Our estimates are $d\ensuremath{\approx}50\AA{},$ $\ensuremath{\lambda}{(L}_{3})=170\AA{},$ and $\ensuremath{\lambda}{(L}_{2})=525\AA{}.$ The ratio $\ensuremath{\lambda}{(L}_{2})/d\ensuremath{\approx}9$ at the ${L}_{2}$ edge indicate that the extent of saturation is comparable to that observed in pure metallic Fe. In contrast, at the ${L}_{3}$ edge, saturation is considerably increased because of the reduced value of $\ensuremath{\lambda}{(L}_{3})/d\ensuremath{\approx}3.5.$ As a consequence, quantitative magnetic studies based on linear and circular dichroism at the $2p$ edges of Fe in magnetic oxides must take into account and correct for saturation effects.