EuBaFe{sub 2}O{sub 5+w}: Valence mixing and charge ordering are two separate cooperative phenomena
- Department of Physics, Abo Akademi, FI-20500 Turku (Finland)
Mixed-valence EuBaFe{sub 2}O{sub 5+w} exhibits a robust Verwey-type transition. The trend in the volume change suggests a first-order transition up to the nonstoichiometry level of about w=0.25. {sup 57}Fe Mossbauer spectroscopy, differential scanning calorimetry and synchrotron X-ray powder diffraction are used to study the valence mixing and charge ordering in EuBaFe{sub 2}O{sub 5+w} as a function of the nonstoichiometry parameter w. {sup 151}Eu Mossbauer spectroscopy is used as a selective probe into the ferromagnetic valence-mixing coupling along c above the Verwey transition, and reveals that increasing w destroys this coupling in favor of a G-type magnetic order in parallel with the progressive removal of the valence-mixed iron states accounted for by {sup 57}Fe Mossbauer spectroscopy. This removal proceeds according to a probability scheme of mixing between ferromagnetically coupled divalent and trivalent neighbor iron atoms along c across the R layer. In contrast, the concentration decrease of the orbital- and charge-ordered states in EuBaFe{sub 2}O{sub 5+w} is found to be a linear function of w. Valence mixing and charge ordering are therefore two separate cooperative phenomena. The enthalpy of the Verwey-type transition between these two cooperative systems is a linear function of w, which suggests that it originates from the latent heat of freezing into the long-range ordered orbital- and charge-ordered state. The enthalpy becomes zero at the nonstoichiometry level of about w=0.25.
- OSTI ID:
- 21015631
- Journal Information:
- Journal of Solid State Chemistry, Vol. 180, Issue 1; Other Information: DOI: 10.1016/j.jssc.2006.09.031; PII: S0022-4596(06)00525-1; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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