We report the first observation of a nonreciprocal x-ray linear dichroism caused by the time-reversal odd, real part zeta of the complex gyrotropy tensor zeta(*) which is dominated by electric dipole-electric quadrupole E1E2 interference terms. A nonreciprocal transverse anisotropy was observed in the low temperature insulating phase of a Cr doped V2O3 Mott crystal when a single antiferromagnetic domain was grown by magnetoelectric annealing along the hexagonal c axis. This new element (edge) specific spectroscopy could nicely complement x-ray magnetic circular dichroism which is silent for antiferromagnetic materials.

This paper is reviewing a number of artefactual limitations in the current EXAFS analysis. In conventional absorption measurements, the major sources of errors are the transmission of harmonics by the monochromator and inevitable leakages of radiation around or through the sample. The consequences are an alteration of the amplitude of the signal but also some harmonic distortion of the EXAFS oscillations and a systematic perturbation of the measured Debye-Waller terms. An efficient correction of the effects of X-ray leakage is suggested whereas the presence or the elimination of harmonics can be assessed by monitoring the reproducibility of the edge jump when calibrated metallic foils of different nature are inserted behind the sample. The basic analysis developed for absorption measurements has been successively extended to the case of REFLEXAFS and various emission techniques : X-ray fluorescence/scattering, optical luminescence and total electron yield. It became possible to rationalize a number of experimental observations and to determine appropriate operating conditions

We report the first observation of natural circular dichroism (CD) in the x-ray region. Measurements at the Nd L 3 edge in single crystals of Na 3 Nd͑digly͒ 3 ? 2NaBF 4 ? 6H 2 O show CD with a dissymmetry factor g ഠ 10 23 of the same order of magnitude as observed in the visible-uv region and ϳ100 times greater than in the vibrational infrared. Calculations using multiple scattering theory (MST) are in excellent agreement with the measured CD in the near-edge region (about 100 eV from the rising edge) and show that the effect arises from the electric dipole-electric quadrupole interference mechanism.[S0031-9007(98)06201-2]

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