Relativistic calculations of spin-dependent x-ray-absorption spectra

Ankudinov, A. L.; Rehr, J. J.

doi:10.1103/physrevb.56.r1712

Cited by 535 publications

(412 citation statements)

References 16 publications

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“…Using an approximate theory of XMCD, investigations of various exchange models were performed at the L 2 and L 3 edges of Gd with half-filled core levels. 12,13 It turned out that sign, amplitude and general form of the XMCD signal agreed reasonably well with experiment. Ebert et al 16 applied a fully relativistic description of MEXAFS to data of the L 2,3 -edges of bcc-Fe taken at the second generation synchrotron BESSYI.…”

Section: Introductionsupporting

confidence: 60%

Bayes-Turchin analysis of x-ray absorption data above the FeL2,3-edges

Rossner¹,

Schmitz²,

Imperia³

et al. 2006

Phys. Rev. B

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Extended x-ray absorption fine structure ͑EXAFS͒ data and magnetic EXAFS ͑MEXAFS͒ data were measured at two temperatures ͑180 and 296 K͒ in the energy region of the overlapping L-edges of bcc Fe grown on a V͑110͒ 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 atomiclike 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 paths were determined by a two parameter forcefield model using a priori values adjusted to Born-von Karman parameters of inelastic neutron scattering data. The investigations of the system Fe/ V͑110͒ demonstrate that the simultaneous fitting of atomic background parameters and EXAFS parameters can be performed reliably. Using the L 2 -and L 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.

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Section: Introductionsupporting

confidence: 60%

Bayes-Turchin analysis of x-ray absorption data above the FeL2,3-edges

Rossner¹,

Schmitz²,

Imperia³

et al. 2006

Phys. Rev. B

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“…67 Data were collected at temperatures between 30 and 400 K using a 60%-tuned Si 220 double crystal monochromator and a harmonic rejection mirror. The EXAFS function was extracted from the raw data and fit to theoretical backscattering functions calculated by the FEFF8 code 68 with the RSXAP analysis package. 69 The amplitude of the first peak vs. temperature is shown in the Supporting Information, Figure S23, demonstrating the loss in amplitude above 330 K. Moreover, there is also a shift of weight in the first peak of the FT to higher distances above 330 K, Figure 12.…”

Section: Methodsmentioning

confidence: 99%

Supramolecular Catalysis of Orthoformate Hydrolysis in Basic Solution: An Enzyme-Like Mechanism

2008

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Abstract. Magnetic susceptibility measurements and X-ray data confirm that tert-butyl substituted manganocenes [(Me 3 C) n C 5 H 5-n ] 2 Mn (n= 1, 2) follow the trend previously observed with the methylated manganocenes, i.e., electron donating groups attached to the Cp ring stabilize the low-spin (LS) electronic ground state relative to Cp 2 Mn and exhibit higher spin-crossover (SCO) temperatures.However, introducing three CMe 3 groups on each ring gives a temperature invariant high-spin (HS) state manganocene. The origin of the high-spin state in [1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Mn is due to the significant bulk of the [1,2,4-(Me 3 C) 3 C 5 H 2 ] -ligand, which is sufficient to generate severe inter-ring steric strain that prevents the realization of the low-spin state. Interestingly, the spin transition in [1,3-(Me 3 C) 2 C 5 H 3 ] 2 Mn is accompanied by a phase transition resulting in a significant irreversible hysteresis (∆T c = 16 K). This structural transition was also observed by extended X-ray absorption fine-structure (EXAFS) measurements. Magnetic susceptibility studies and X-ray diffraction data on SiMe 3 substituted 2 manganocenes [(Me 3 Si) n C 5 H 5-n ] 2 Mn (n= 1, 2, 3) show high-spin configuration in these cases. Although tetra-and hexasubstituted manganocenes are high-spin at all accessible temperatures, the disubstituted manganocenes exhibit a small low-spin admixture at low temperature. In this respect it behaves similarily to [(Me 3 C)(Me 3 Si)C 5 H 3 ] 2 Mn, which has a constant low-spin admixture up to 90 K and then gradually converts to high-spin. Thermal spin-trapping can be observed for [(Me 3 C)(Me 3 Si)C 5 H 3 ] 2 Mn on rapid cooling.

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“…Uranium EXAFS scans were processed using the computer programs Athena [6,31,32], SixPACK [33], and Feff7 [34] (Supporting Information). The conceptual physical model of uranium in these systems consists of three components: uranium is either i) adsorbed to Fe (hydr)oxide surfaces, ii) incorporated into Fe (hyrd)oxide structure, or iii) reduced to U(IV) as UO 2(s) .…”

Section: Solid Phase Analysismentioning

confidence: 99%

Incorporation of Oxidized Uranium into Fe (Hydr)oxides during Fe(II) Catalyzed Remineralization

Nico

Stewart

Fendorf

2009

Environ. Sci. Technol.

119

132

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The form of solid phase U after Fe(II) induced anaerobic remineralization of ferrihydrite in the presence of aqueous and absorbed U(VI) was investigated under both abiotic batch and biotic flow conditions. Experiments were conducted with synthetic ground waters containing 0.168 mM U(VI), 3.8 mM carbonate, and 3.0 mM Ca 2+ . In spite of the high solubility of U(VI) under these conditions, appreciable removal of U(VI) from solution was observed in both the abiotic and biotic systems. The majority of the removed U was determined to be substituted as oxidized U (U(VI) or U(V)) into the octahedral position of the goethite and magnetite formed during ferrihydrite remineralization. It is estimated that between 3% and 6% of octahedral Fe(III) centers in the new Fe minerals were occupied by U(VI). This site specific substitution is distinct from the non-specific U co-precipitation processes in which uranyl compounds, e.g. uranyl hydroxide or carbonate, are entrapped with newly formed Fe oxides. The prevalence of site specific U incorporation under both abiotic and biotic conditions and the fact that the produced solids were shown to be resistant to both extraction (30 mM KHCO 3 ) and oxidation (air 2 for 5 days) suggest the potential importance of sequestration in Fe oxides as a stable and immobile form of U in the environment.

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Relativistic calculations of spin-dependent x-ray-absorption spectra

Cited by 535 publications

References 16 publications

Bayes-Turchin analysis of x-ray absorption data above the FeL2,3-edges

Bayes-Turchin analysis of x-ray absorption data above the FeL2,3-edges

Supramolecular Catalysis of Orthoformate Hydrolysis in Basic Solution: An Enzyme-Like Mechanism

Incorporation of Oxidized Uranium into Fe (Hydr)oxides during Fe(II) Catalyzed Remineralization

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