Ab initio theory and calculations of X-ray spectra

Rehr, J. J.; Kas, J. J.; Prange, Micah P.; Sorini, A. P.; Takimoto, Y.; Vila, Fernando D.

doi:10.1016/j.crhy.2008.08.004

Cited by 519 publications

(442 citation statements)

References 59 publications

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“…The EXAFS spectra were modelled using ARTEMIS 28 and FEFF6.0 29 for the theoretical calculations based on crystal structures obtained by DFT calculations in this study. For monometallic CoAlPO, the EXAFS models include single scattering O paths with Co-O distances of 1.87 Å and two single scattering P path with Co-P distance of 3.1 and 3.4 Å.…”

Section: Exafs Modellingmentioning

confidence: 99%

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

et al. 2015

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A combined electronic structure computational and X-ray absorption spectroscopy study was used to investigate the nature of the active sites responsible for catalytic synergy in Co-Ti bimetallic nanoporous frameworks. Probing the nature of the molecular species at the atomic level has led to the identification of a unique Co-O-Ti bond, which serves as the loci for the superior performance of the bimetallic catalyst, when compared with its analogous monometallic counterpart. The structural and spectroscopic features associated with this active site have been characterized and contrasted, with a view to affording structureproperty relationships, in the wider context of designing sustainable catalytic oxidations with porous solids.

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Section: Exafs Modellingmentioning

confidence: 99%

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

et al. 2015

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“…In particular, we highlight the noncollinear magnetic structure in Mn 3 Ga evidenced by neutron diffraction and make estimates of the direction and magnitude of the orbital moments on each crystallographic site. Finally, we compare our experimental findings with density functional theory (DFT) calculations of the electronic structure and magnetic properties of the D0 22 -structure Mn 3 Ga.…”

Section: Introductionmentioning

confidence: 99%

“…While the cubic L2 1 Heusler alloys are virtually isotropic, their tetragonal cousins can display very high uniaxial magnetic anisotropy coupled with tunable saturation magnetization and high spin polarization. This is especially true in the case of D0 22 Mn 3 Ga. [15][16][17][18] Thin films of this material exhibit high, perpendicular, uniaxial anisotropy and grow with ease on both MgO and SrTiO 3 substrates, as well as a number of lattice matched seed layers like Cr and Pt.…”

Section: Introductionmentioning

confidence: 99%

“…Further details regarding the growth and characterization of thin films on MgO and on seed layers of Pt and Cr are published elsewhere. 15,16 Mn 3 Ga crystallizes in the D0 22 structure, space group number 139, I 4/mmm with Mn in two nonequivalent sites, Wyckoff positions 2b and 4d while Ga occupies the 2a position. Mn spins in the 2b positions couple ferromagnetically to each other and antiferromagnetically to those of Mn in the 4d position.…”

Section: Structural and Magnetic Propertiesmentioning

confidence: 99%

“…If this disorder is complete, this material has a c/a ratio >1, leading to easy-axis anisotropy. 20,21 In the case of a partially ordered D0 22 . We find that at higher values of the order parameter, the ratio between the in-plane and the out-of-plane saturation moments increases, indicating that the noncollinearity of the magnetic structure in Mn 3 Ga is not due to disorder.…”

Section: Structural and Magnetic Propertiesmentioning

confidence: 99%

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Site-specific order and magnetism in tetragonal Mn3Ga thin films

et al. 2013

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Mn 3 Ga bulk material and thin films deposited on several different substrates have been investigated using x-ray and neutron diffraction, x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and electronic structure calculations using density-functional theory with the aim of determining the atomic site occupancy, magnetic moments, and magnetic structure of this tetragonal D0 22 -structure compound. The Mn 3 Ga has close to ideal site occupancy, with Ga on 2a sites and Mn on 2b and 4d sites. The magnetic structure is basically ferrimagnetic, with the larger Mn moment of about 3 μ B on the 2b site, which is coordinated by 8 Mn 4d and 4 Ga, and the smaller one on the 4d site, which is coordinated by 4 Mn 2b, 4 Ga, and 4 Mn 4d. The Mn d-band occupancy is close to 5 on both sites, and the orbital moments are small, <0.2 μ B . The material nevertheless exhibits substantial uniaxial anisotropy, K u = 1.0 MJ m −3 , which originates from the 4d site. The 2b site has hard axis anisotropy, which together with an oscillatory exchange coupling from the first and second nearest neighbors, leads to a soft component of the magnetization in the c plane, coexisting with c-axis hysteresis loops exhibiting coercivity of up to 1.2 T, and magnetization in the range 110-220 kA m −1 at room temperature, depending on preparation conditions. Tetragonal Mn 2 Ga films behave similarly. Manganese is lost from both sites, but the films have substantially larger magnetization (480 kA m −1 ) and anisotropy constant (2.35 MJ m −3 ) than Mn 3 Ga.

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XAFSSpectroscopy

Heald

2012

Characterization of Materials

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The x‐ray absorption fine structure (XAFS) that is present near x‐ray absorption edges contains detailed information about the local structure and bonding of the absorbing atoms. With the advent of intense tunable sources of x‐rays using synchrotron radiation facilities, the application of x‐ray absorption spectroscopy has become widespread and routine. The XAFS is a local probe sensitive to the location and type of atoms surrounding the absorbing atom. As a local probe, it can be applied to many materials where diffraction‐based techniques would be impractical such as resolving the structure near highly dilute components and determining the local structure of atoms in nanoparticles, liquids, metalloproteins in solution, amorphous solids, and poorly crystalline materials. In addition to the direct structural information, the absorption edge position and shape can be used to determine the site symmetry and valence of the absorbing atoms. This chapter describes the physical principles that result in the fine structure, basic experimental techniques, and basic principles for the extraction of the information present in the spectra. It also touches on some of the unique aspects of performing measurements at a synchrotron radiation facility.

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Ab initio theory and calculations of X-ray spectra

Cited by 519 publications

References 59 publications

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

Site-specific order and magnetism in tetragonal Mn3Ga thin films

XAFSSpectroscopy

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