On experimental attenuation factors of the amplitude of the EXAFS oscillations in absorption, reflectivity and luminescence measurements

Goulon, J.; Goulon-Gìnet, C.; Cortès, R.; Dubois, Jean

doi:10.1051/jphys:01982004303053900

Cited by 211 publications

(91 citation statements)

References 19 publications

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“…The x-ray-absorption spectra for right and left circularly polarized x-ray beams were done assuming semiinfinite samples, but taking into account the various background contributions (fluorescence of subshells and matrix as well as coherent and incoherent scattering), the angle of incidence of the x-ray beam, and finally the solid angle of the detector [46][47][48].…”

Section: Methodsmentioning

confidence: 99%

X-ray magnetic circular dichroism experiments and theory of transuranium Laves phase compounds

et al. 2013

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The actinide cubic Laves compounds NpAl2, NpOs2, NpFe2, and PuFe2 have been examined by X-ray magnetic circular dichroism (XMCD) at the actinide M4,5 absorption edges and Os L2,3 absorption edges. They have the interesting feature that the An−An spacing is close to the so-called Hill limit so that substantial hybridization between the 5f states on neighboring atoms is expected to occur. The XMCD experiments performed at the M4,5 absorption edges of Np and Pu allow us to determine the spectroscopic branching ratio, which gives information on the coupling scheme in these materials. In all materials the intermediate coupling scheme is found appropriate. Comparison with the SQUID data for NpOs2 and PuFe2 allows a determination of the individual orbital and spin magnetic moments and the magnetic dipole contribution m md . The resulting orbital and spin magnetic moments are in good agreement with earlier values determined by neutron diffraction, and the values of m md are non-negligible, and close to those predicted for intermediate coupling. There is a comparatively large induced moment on the Os atom in NpOs2 such that the Os contribution to the total moment per formula unit is ∼30% of the total. The spin and orbital moments at the Os site are parallel, in contrast to the anti-parallel configuration of Os impurities in 3d ferromagnetic transition metals. Calculations using the LDA+U technique are reported. The ab initio computed XMCD spectra show good agreement with experimental spectra for small values (0-1eV) of the Hubbard U parameter, which underpins that 5f electrons in these compounds are relatively delocalized. The calculations confirm the sign and magnitude of the experimentally determined induced magnetic moments on the Os site in NpOs2. A posteriori, by comparison of the theoretical and measured XMCD spectra, we can determine the most appropriate LSDA+U variant and the value of U.

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Section: Methodsmentioning

confidence: 99%

X-ray magnetic circular dichroism experiments and theory of transuranium Laves phase compounds

et al. 2013

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“…2) the fundamental absorption coeflicient from the measured one by using the following equation: monic elimination. The higher harmonics (above the fundamental one) produce more distortion of the EXAFS signal than the lower ones [1][2][3]. Only 6% of the third harmonic intensity (see Fig.…”

Section: General Stepmentioning

confidence: 99%

“…Commonly suggested methods with the use e.g. of total reflection Au mirrors or direct computational methods [1] require knowledge of the mass absorption coefficients for investigated substance and additional structural data (as exact chemical composition, density etc.). It is shown that the existence of high harmonics in the spectrum requires correction especially for samples with a high atomic number.…”

Section: Corrections On the "Sample Holes"mentioning

confidence: 99%

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Computational Method of X-Ray Harmonic Elimination in EXAFS Treating

Ovsjannikov

1994

Acta Phys. Pol. A

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The computational method of EXAFS amplitude correction by harmonics elimination and intensity leakage assessment has been worked out. In conventional absorption measurements, the major sources of errors are the transition of harmonics by the monochromator and inevitable leakage of radiation around and (or) through the sample. In this paper we present the method of the effective corrections being based on the measurements of the intensity of X-ray radiation passed through calibrated metal foils both without and together with investigated samples. As the advantage of the method one may emphasise the fact that it does not require any additionał data for the investigated samples such as chemicał composition, density, table absorption coefficients.

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“…The spectra have been corrected for self-absorption effects and for incomplete circular polarization rates of incident x-ray photons. The self-absorption corrections were done in the semi-infinite sample approximation, taking into account the chemical composition, the density, the background contributions (fluorescence of subshells and matrix, coherent and incoherent scattering), and the geometrical factors [29][30][31] . The Np edge-jump intensity ratio M 5 /M 4 has been normalized to 1.57, the value reported in the XCOM tables by Berger et al in Ref.…”

Section: F Xmcd Spectramentioning

confidence: 99%

Low-temperature magnetic properties ofNpNi5

et al. 2014

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We present the result of an extended experimental characterization of the hexagonal intermetallic Haucke compound NpNi5. By combining macroscopic and shell-specific techniques, we determine the 5f -shell occupation number n f close to 4 for the Np ions, together with orbital and spin components of the ordered moment in the ferromagnetic phase below TC = 16 K (µS = -1.88 µB and µL = 3.91 µB). The apparent coexistence of ordered and disordered phases observed in the Mössbauer spectra is explained in terms of slow relaxation between the components of a quasi-triplet ground state. The ratio between the expectation value of the magnetic dipole operator and the spin magnetic moment (3 Tz / Sz = +1.43) is positive and large, suggesting a localized character of the 5f electrons. The angular part of the spin-orbit coupling ( ℓ · s = -5.55) is close to the value of -6.25 calculated for trivalent Np ions in intermediate coupling approximation. The results are discussed against the prediction of first-principle electronic structure calculations based on the spin-polarized local spin density approximation plus Hubbard interaction, and of a mean field model taking into account crystal field and exchange interactions.

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On experimental attenuation factors of the amplitude of the EXAFS oscillations in absorption, reflectivity and luminescence measurements

Cited by 211 publications

References 19 publications

X-ray magnetic circular dichroism experiments and theory of transuranium Laves phase compounds

X-ray magnetic circular dichroism experiments and theory of transuranium Laves phase compounds

Computational Method of X-Ray Harmonic Elimination in EXAFS Treating

Low-temperature magnetic properties ofNpNi5

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