Iron orbital occupancies upon valence mixing of charge-ordered GdBaFe II Fe III O 5

Mössbauer spectra of charge-ordered/valence-mixed GdBaFe 2 O 5 have been analyzed in order to determine the orbital occupancies of the minority-spin d electron as a function of temperature. In the charge-ordered state below the Verwey temperature T V , it occupies the Fe 2+ d xz orbital, which is ordered. Above T V , the electron partially occurs also at the trivalent iron and spreads over two additional orbitals, d_x^2-y^2 and d_z^2 . In the valence-mixing state (above T p ) also orbital d yz participates. The study illustrates how the Mössbauer electric-field gradient, center shift and internal field jointly reflect the distribution of the minority-spin electron culprit behind the Verwey transition.