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J L Hodeau

Publications and source records attributed to J L Hodeau.

4 recordsLinked to original sources
PubMed2001

Structural evidence for Ta-tetramerization displacements in the charge-density-wave compound (TaSe4)2I from x-ray anomalous diffraction.

We use the anomalous x-ray diffraction technique to investigate the nature of the tantalum displacement pattern in the modulated phase of the charge-density-wave compound (TaSe4)2I. In addition to the known acousticlike modulation, we find the first direct evidence for the condensation of opticlike Ta displacements along the metallic chains corresponding to an LLSS pattern of long and short in-chain Ta-Ta distances (Ta-tetramerization modes). This result confirms a previous model in which the interaction of the electronically coupled optic modes with long-wavelength acoustic shear modes leads to the condensation of a modulation of mixed character.

Journal Article↗
PubMed2001

Diffraction anomalous fine structure of forbidden Bragg reflections: charge localization and structure of the octahedral site in magnetite.

Resonant X ray scattering has been used to investigate charge localization on the octahedral iron atoms in magnetite below and above the Verwey temperature. We have measured the DAFS spectra of the 002 and 006 "forbidden" Bragg reflections permitted by the anisotropy of the iron anomalous scattering factor. We performed ab initio calculations which are in fair agreement with the experiment in the near edge region and demonstrate the sensitivity of the DAFS spectra to tiny structural and electronic changes. No change is observed, in the energy and azimuthal dependences, when the sample is cooled down below the Verwey temperature. Charge ordering can be definitely excluded and different charge localisation schemes discarded. Ab initio simulations, performed by using the refined crystallographic structure proposed for the room temperature phase, do not show a good agreement with the experiment in the extended region of the DAFS spectrum. This point is being investigated.

Journal Article↗
PubMed2000

Resonant "forbidden" reflections in magnetite.

Resonant x-ray scattering was used to investigate electronic fluctuations of the octahedral iron atoms in magnetite. We measured the (002) and (006) "forbidden" x-ray diffraction reflections permitted by the anisotropy of the iron anomalous scattering factor. The energy and azimuthal angle dependencies of these reflections, and the polarization analysis, are shown and discussed. The results clearly show p and d iron empty states ordering in magnetite at room temperature. Moreover, the octahedral iron atoms are electronically equivalent in a time scale lower than 10(-16) sec. Therefore, magnetite should be considered as an itinerant magnet and not as a fluctuating mixed valence material.

Journal Article↗