Biomedical subjects

Y Joly

Publications and source records attributed to Y Joly.

11 recordsLinked to original sources

PubMed2001

Natural linear dichroism in pyrite (FeS2): experiments and calculations.

Electric quadrupole transitions are revealed through the angular dependence of X-ray absorption spectra in a cubic crytal. Data collection was achieved at the iron K-edge in pyrite (FeS2) by using the angular moment method developed for X-ray Natural Circular Dichoism (XNCD) measurements. The natural linear dichroism (XNLD) was found to be around 0.5% of the edge jump. Experimental results are compared with monelectronic and multilectronic calculations. Calculations allow to quantitatively determine the proportion of quadrupolar transitions in the pre-edge structure and the anisotropy is explained in terms of structural and electronic parameters.

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↗

PubMed1996