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

Yohan Guyodo (1) , Philippe Sainctavit (1) , Marie-Anne Arrio (1) , Claire Carvallo (1) , R Lee (2) , Jasmine J. Erbs (2) , Brady S. Forsberg (2) , Guillaume Morin (3) , Fabien Maillot (4) , France Lagroix (5) , Pierre Bonville (6) , Fabrice Wilhelm (7) , Andrei Rogalev (7)

1 IMPMC - Institut de minéralogie et de physique des milieux condensés
2 Department of Chemistry [Minneapolis]
3 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
4 CHRU Tours - Centre Hospitalier Régional Universitaire de Tours
5 IPGP - Institut de Physique du Globe de Paris
6 SPEC - UMR3680 - Service de physique de l'état condensé
7 ESRF - European Synchrotron Radiation Facility

[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.

Keywords: XMCD; ferrihydrite; magnetic properties Index

Domains: Sciences of the Universe [physics]

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, 2012, 13, ⟨10.1029/2012GC004182⟩. ⟨insu-01311104⟩