Electronic states ofRFe2O4(R=Lu,Yb,Tm,Y)mixed-valence compounds determined by soft x-ray absorption spectroscopy and x-ray magnetic circular dichroism

Abstract

We here report an investigation of the electronic states in the $R\mathrm{F}{\mathrm{e}}_{2}{\mathrm{O}}_{4}(R=\mathrm{Lu},\phantom{\rule{0.16em}{0ex}}\mathrm{Yb},\phantom{\rule{0.16em}{0ex}}\mathrm{Tm},\phantom{\rule{0.16em}{0ex}}\mathrm{Y})$ mixed-valence ferrites by means of soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements together with ab initio theoretical calculations. The presence of ${\mathrm{Fe}}^{+2}$ and ${\mathrm{Fe}}^{+3}$ pure ionic species is discarded in the XAS spectra at the $\mathrm{O}\phantom{\rule{0.16em}{0ex}}K$ edge in both experimental data and simulations based on the multiple scattering theory. Similarly, no trace of $\mathrm{F}{\mathrm{e}}^{+2}/\mathrm{F}{\mathrm{e}}^{+3}$ contributions is detected in the XMCD spectra at the $\mathrm{Fe}\phantom{\rule{0.16em}{0ex}}K$ edge. On the other hand, the XAS and XMCD spectra at the $\mathrm{Fe}\phantom{\rule{0.16em}{0ex}}{L}_{2,3}$ edges can be well described in terms of $\mathrm{F}{\mathrm{e}}^{+2}/\mathrm{F}{\mathrm{e}}^{+3}$ contributions, and are also supported by multiplet calculations. This finding can be interpreted as the existence of a mixture of $3{d}^{5}/3{d}^{6}$ configurations at the Fe atoms. Alternative ferrimagnetic spin orderings based on a trimodal Fe valence distribution are also proposed and discussed. Finally, a possible explanation for the strong dependence of the $\mathrm{Fe}\phantom{\rule{0.16em}{0ex}}{L}_{2,3}$ edges XMCD signal magnitude on both the sample surface preparation and detection method is presented.