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X-ray magnetic circular dichroïsm provides strong evidence for tetrahedral iron in ferrihydrite

Abstract : [1] Ferrihydrite is an important iron oxyhydroxide for earth and environmental sciences, biology, and technology. Nevertheless, its mineral structure remains a matter of debate. The stumbling block is whether a significant amount of tetrahedrally coordinated iron is present. Here we present the first X-ray magnetic circular dichroïsm (XMCD) measurements performed on a well characterized synthetic sample of 6-line fer-rihydrite, at both K and L 2,3 energy edges of iron. XMCD results demonstrate unambiguously the presence of tetrahedrally coordinated Fe(III) in the mineral structure, in quantities compatible with the latest extended X-ray absorption fine structure (EXAFS) analyses suggesting a concentration of 20–30%. Moreover , we find an antiferromagnetic coupling between tetrahedral and octahedral sublattices, with the octa-hedral sublattice parallel to the external magnetic field. Components: 5100 words, 3 figures.
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Yohan Guyodo, Philippe Sainctavit, Marie-Anne Arrio, Claire Carvallo, R Lee, et al.. X-ray magnetic circular dichroïsm provides strong evidence for tetrahedral iron in ferrihydrite. Geochemistry, Geophysics, Geosystems, AGU and the Geochemical Society, 2012, 13, ⟨10.1029/2012GC004182⟩. ⟨insu-01311104⟩

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