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

We show that the absorption spectra of magnetic iron oxides $({\mathrm{Fe}}_3{\mathrm{O}}_4,\hspace{0.5em}\alpha -{\mathrm{Fe}}_2{\mathrm{O}}_3)$ 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 (λ), and their ratio $(\lambda /d).\mathrm{}$ Our estimates are $d\approx 50\AA ,$ $\lambda {(L}_3)=170\mathrm{}\AA ,$ and $\lambda {(L}_2)=525\mathrm{}\AA .$ The ratio $\lambda {(L}_2)/d\approx 9$ 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 $\lambda {(L}_3)/d\approx \mathrm{3.5.}$ 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.