skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Bayes-Turchin Analysis of Overlapping L-Edges EXAFS Data of Iron

Abstract

Spin polarized and spin averaged extended x-ray absorption fine structure ((M)EXAFS) data were measured at temperatures of 180 K and 296 K in the soft x-ray energy regime of the overlapping L-edges of an iron film grown on V(110). The absorption coefficients were analyzed with the Bayes-Turchin procedure. The analysis yields the correction function to the atomic-like background-absorption coefficient calculated by FEFF8 and reveals components of atomic EXAFS oscillations. The EXAFS Debye-Waller (DW) parameters were determined. Their split into a thermal and a structural contribution was not possible without theoretical input since the two temperatures in this experiment were not sufficiently far apart from each other and the k range of the data was too small. The a priori values of the thermal contribution to the DW parameters were therefore derived from a force-field model with two spring constants. They were adjusted to DW parameters calculated from Born-von Karman force constants which had been obtained from inelastic neutron scattering. Those two spring constants also nicely reproduce the unprojected vibrational density of states deduced from phonon dispersion curves. The MEXAFS oscillations can be described by the rigid-band model and the L2- and L3-EXAFS components. A negative exchange-related energy is obtained bymore » fitting the MEXAFS signal in the extended energy region. This is in contrast to the predictions of the Hedin-Lundquist functional and the Dirac-Hara functional used in the FEFF8 code.« less

Authors:
; ; ;  [1];  [2]
  1. Hahn-Meitner-Institut Berlin, Glienicker Str. 100, D-14109 Berlin (Germany)
  2. Department of Physics, University of Washington, Seattle, Washington 98195.1560 (United States)
Publication Date:
OSTI Identifier:
21054724
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 882; Journal Issue: 1; Conference: XAFS13: 13. international conference on X-ray absorption fine structure, Stanford, CA (United States), 9-14 Jul 2006; Other Information: DOI: 10.1063/1.2644432; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; CORRECTIONS; CRYSTAL STRUCTURE; DEBYE-WALLER FACTOR; DISPERSION RELATIONS; F CODES; FILMS; FINE STRUCTURE; INELASTIC SCATTERING; IRON; NEUTRON DIFFRACTION; PHONONS; SOFT X RADIATION; SPIN; SPIN ORIENTATION; TEMPERATURE DEPENDENCE; VANADIUM; X-RAY SPECTROSCOPY

Citation Formats

Rossner, H. H., Schmitz, D., Imperia, P., Krappe, H. J., and Rehr, J. J.. Bayes-Turchin Analysis of Overlapping L-Edges EXAFS Data of Iron. United States: N. p., 2007. Web. doi:10.1063/1.2644432.
Rossner, H. H., Schmitz, D., Imperia, P., Krappe, H. J., & Rehr, J. J.. Bayes-Turchin Analysis of Overlapping L-Edges EXAFS Data of Iron. United States. doi:10.1063/1.2644432.
Rossner, H. H., Schmitz, D., Imperia, P., Krappe, H. J., and Rehr, J. J.. Fri . "Bayes-Turchin Analysis of Overlapping L-Edges EXAFS Data of Iron". United States. doi:10.1063/1.2644432.
@article{osti_21054724,
title = {Bayes-Turchin Analysis of Overlapping L-Edges EXAFS Data of Iron},
author = {Rossner, H. H. and Schmitz, D. and Imperia, P. and Krappe, H. J. and Rehr, J. J.},
abstractNote = {Spin polarized and spin averaged extended x-ray absorption fine structure ((M)EXAFS) data were measured at temperatures of 180 K and 296 K in the soft x-ray energy regime of the overlapping L-edges of an iron film grown on V(110). The absorption coefficients were analyzed with the Bayes-Turchin procedure. The analysis yields the correction function to the atomic-like background-absorption coefficient calculated by FEFF8 and reveals components of atomic EXAFS oscillations. The EXAFS Debye-Waller (DW) parameters were determined. Their split into a thermal and a structural contribution was not possible without theoretical input since the two temperatures in this experiment were not sufficiently far apart from each other and the k range of the data was too small. The a priori values of the thermal contribution to the DW parameters were therefore derived from a force-field model with two spring constants. They were adjusted to DW parameters calculated from Born-von Karman force constants which had been obtained from inelastic neutron scattering. Those two spring constants also nicely reproduce the unprojected vibrational density of states deduced from phonon dispersion curves. The MEXAFS oscillations can be described by the rigid-band model and the L2- and L3-EXAFS components. A negative exchange-related energy is obtained by fitting the MEXAFS signal in the extended energy region. This is in contrast to the predictions of the Hedin-Lundquist functional and the Dirac-Hara functional used in the FEFF8 code.},
doi = {10.1063/1.2644432},
journal = {AIP Conference Proceedings},
number = 1,
volume = 882,
place = {United States},
year = {Fri Feb 02 00:00:00 EST 2007},
month = {Fri Feb 02 00:00:00 EST 2007}
}
  • Extended x-ray absorption fine structure (EXAFS) data and magnetic EXAFS (MEXAFS) data were measured at two temperatures (180 and 296 K) in the energy region of the overlapping L-edges of bcc Fe grown on a V(110) crystal surface. In combination with a Bayes-Turchin data analysis procedure these measurements enable the exploration of local crystallographic and magnetic structures. The analysis determined the atomic-like background together with the EXAFS parameters which consisted of ten shell radii, the Debye-Waller parameters, separated into structural and vibrational components, and the third cumulant of the first scattering path. The vibrational components for 97 different scattering pathsmore » were determined by a two parameter force-field model using a priori values adjusted to Born-von Karman parameters of inelastic neutron scattering data. The investigations of the system Fe/V(110) demonstrate that the simultaneous fitting of atomic background parameters and EXAFS parameters can be performed reliably. Using the L{sub 2}- and L{sub 3}-components extracted from the EXAFS analysis and the rigid-band model, the MEXAFS oscillations can only be described when the sign of the exchange energy is changed compared to the predictions of the Hedin Lundquist exchange and correlation functional.« less
  • Specular reflectivity of {ital p}-polarized light near the iron {ital L}{sub II} and {ital L}{sub III} absorption edges was measured from a single-crystal iron film with an external magnetic field perpendicular to the scattering plane. Large changes in reflectivity were observed upon reversal of the direction of the magnetic field. We attribute this resonant magnetization-sensitive effect to the interference between magnetic and nonmagnetic contribution to the resonant scattering. Similar effects can be expected in other ferromagnetic and ferrimagnetic systems.
  • The soft-x-ray absorption and magnetic circular dichroism (MCD) cross sections at the {ital L}{sub 2} and {ital L}{sub 3} core-level edges of Ni and Fe have been calculated using a one-electron tight-binding band-structure approach. The tight-binding scheme is taken from the work of Papaconstantopoulos, supplemented with the inclusion of spin-orbit coupling in the {ital d} bands and fully relativistic dipole selection rules. In Ni, a fit to the various {ital L}{sub 2} and {ital L}{sub 3} intensity ratios can be achieved, but only with values of the {ital d}-band spin-orbit parameter {xi} and exchange parameter {Delta}{sub ex} at variance withmore » the ground-state band-structure values. For Fe, there is no plausible value of {xi} capable of explaining the intensity ratios; also, the predicted substructure within the {ital L}{sub 2} and {ital L}{sub 3} white lines is not seen in experiment. These failures of the one-electron approach are qualitatively consistent with expected many-body electronic rearrangements associated with core-hole creation. Some discussion is offered on sum rules and on orbital versus spin magnetic moments.« less
  • We present a systematic x-ray magnetic circular dichroism (XMCD) study performed at the rare-earth L{sub 2,3} edges in R(Al{sub 1-x}Fe{sub x}){sub 2} Laves phase compounds. The progressive substitution of Al by Fe reveals the existence of a non-negligible contribution of Fe to the rare-earth XMCD spectra. This contribution has been isolated and shown to be similar to the dichroic spectrum recorded at the Fe K edge. These results open the possibility of monitoring the Fe magnetism in lanthanides-iron intermetallic compounds by probing the rare-earth L{sub 2,3}-edge x-ray absorption edges.
  • A whole body counter (WBC) designed to measure bremsstrahlung from 90Y, the short-lived daughter of 90Sr, has been used since 1974 to measure 90Sr-body burdens in residents along the Techa River, which was contaminated by releases from the Mayak Production Association. Bayes' rule has been applied to the a posteriori WBC data in order to derive the uncertainties associated with the data: The lower limit of reliable detection is 2.0kBq and the uncertainty of routine measurements is 1.6kBq.