Bulk-sensitive photoemission spectroscopy of $A_2{\mathrm{FeMoO}}_6$ double perovskites $(A=\mathrm{Sr},\mathrm{Ba})$

The electronic structures of ${\mathrm{Sr}}_2{\mathrm{FeMoO}}_6$ (SFMO) and ${\mathrm{Ba}}_2{\mathrm{FeMoO}}_6$ (BFMO) double perovskites have been investigated using Fe $2\overrightarrow{p}3d$ resonant photoemission spectroscopy (PES) and the Cooper minimum in the Mo $4d$ photoionization cross section. The states close to the Fermi level are found to have a strongly mixed Mo–Fe $t_{2g}$ character, indicating that the Fe valence is far from pure $3+.$ The Fe ${2p}_{3/2}$ x-ray absorption spectroscopy spectra reveal the mixed-valent ${\mathrm{Fe}}^{3+}–{\mathrm{Fe}}^{2+}$ configurations, and a larger ${\mathrm{Fe}}^{2+}$ component for BFMO than for SFMO, suggesting an operative double exchange interaction. The valence-band PES spectra reveal good agreement with the local-spin-density-approximation $\left(\mathrm{LSDA}\right)+U$ calculation.