Orbital occupancy evolution across spin- and charge-ordering transitions in YBaFe 2 O 5

Abstract

A B S T R A C TThermal evolution of the Fe 2+ -Fe 3+ valence mixing in YBaFe 2 O 5 is investigated using Mössbauer spectroscopy. In this high-spin double-cell perovskite, the d 6 and d 5 Fe states differ by the single minority-spin electron which then controls all the spin-and charge-ordering transitions. Orbital occupancies can be extracted from the spectra in terms of the (2013)045127. When the remaining 7% of entropy is supplied at a subsequent transition, the mixing electron couples the two Fe atoms predominantly via their d z 2 orbitals. The valence mixing concerns more than 95% of the Fe atoms present in the crystalline solid; the rest is semiquantitatively interpreted as domain walls and antiphase boundaries formed upon cooling through the Néel and Verwey-transition temperatures, respectively.

Mössbauer study of magnetism in Fe3Se4

“…This would then bring down the internal field considerably as a dipolar contribution can be several tens of Tesla. [15] As Fe 3 Se 4 is probably more covalent than ionic it is hard to make reliable estimates of the contributions to the internal field, even the spin-only contribution mediated by the Fermi-contact interaction may vary. As high-spin Fe 3+ has a magnetic moment of 5 µ B the intermediate-spin magnetic moment is 3 µ B , but when the formal valence is +2.67 the intermediate magnetic moment and corresponding internal field could be roughly 3.67 µ B & 38.9 T or 2.33 µ B & 24.7 T, depending on how the fractional valence affects the moment.…”

“…Point-charge calculations for the selenium ions contribution to the electric field gradient acting on the Fe nuclei gave rather modest values for V zz , indicating that there must be a substantial valence electron contribution, no doubt caused by the intermediate-spin configuration, because a substantial dipolar contribution is also connected to a large valence-electron contribution to the electric field gradient. [15] Non-zero η values are to be expected for a monoclinic structure, but generally η is notoriously hard to fit reliably. Except around T C η remained close to 0.6 for site 1 and 0.4 for site 2, i.e.…”

Spin waves above and below the Verwey transition in TbBaFe2O5

“…Comparing the FV-best-fit parameters to the CO-best-fit parameters shows a reduction in all antiferromagnetic interactions in the FV state as may be due to the introduction of ferromagnetic interactions: J ab = 2.2 ± 0.3 meV, J cS = 1.7 ± 0.7 meV, and J cL = 2.4 ± 0.3 meV. A Mössbauer study of YBFO [16] determined from modeling orbital populations that valence mixing takes place across the bond that we label J cS in Fig. 2, which is ferromagnetic from the static magnetic structure and weakly so in our spin wave model.…”