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Mössbauer spectra of charge-ordered/valence-mixed GdBaFeO 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, it occupies the Fe d orbital, which is ordered. Above T, 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) also orbital d 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. [ABSTRACT FROM AUTHOR]

Samples of pure ferric, ferrous and mixed valence freudenbergite were prepared by different techniques. The Fe Mössbauer spectra of the single valence samples showed poorly resolved quadrupole splittings for the ferric sample, two well-resolved quadrupole splittings for the ferrous sample and electron hopping at, and above, room temperature for the mixed valence sample, which disappeared on lowering the temperature to 50 K. [ABSTRACT FROM AUTHOR]

In mixed-valence manganites, the doped iron species play the roles of simultaneous probes and ruiners for the orbital order occurring in the Mn-O electronic subsystem. We investigated the Mn-based undoped system RBaMnO and the half-doped systems RBaMnO, and RBaMnO substituting a tiny portion of Mn sites with Fe. Single-site Mössbauer spectra were observed at room temperature in the charge-orbitally ordered state, i.e., below T, for R=Y, Sm, Gd. Size of the rare earth ion strongly influences the quadrupole splitting in RBaMnO, but not in RBaMnO. [ABSTRACT FROM AUTHOR]

Iron mixed-valence complex, (n-C3H7)4N[FeIIFeIII(dto)3] (dto = C2O2S2), shows a charge transfer phase transition around 120 K and a ferromagnetic transition at 6.5 K. In order to control the charge transfer phase transition by changing the cation size, we synthesized (n-CnH2n+1)4- N[FeIIFeIII(dto)3] (n=3–6) and investigated the charge transfer phase transition by means of 57Fe Mössbauer spectroscopy. The charge transfer phase transition takes place around 120 K for n=3 and 4, while it does not take place between 300 K and 4 K for n=5 and 6. [ABSTRACT FROM AUTHOR]

Iron mixed-valence complex, (n-C3H7)4N[FeIIFeIII(dto)3] (dto = C2O2S2), shows a charge transfer phase transition around 120 K and a ferromagnetic transition at 6.5 K. In order to control the charge transfer phase transition by changing the cation size, we synthesized (n-CnH2n+1)4- N[FeIIFeIII(dto)3] (n=3–6) and investigated the charge transfer phase transition by means of 57Fe Mössbauer spectroscopy. The charge transfer phase transition takes place around 120 K for n=3 and 4, while it does not take place between 300 K and 4 K for n=5 and 6. [ABSTRACT FROM AUTHOR]