Ch. Brouder

Multiple-scattering theory of x-ray magnetic circular dichroism: Implementation and results for the iron K edge

An implementation of the multiple-scattering approach to x-ray magnetic circular dichroism (XMCD) in K edge x-ray absorption spectroscopy is presented. The convergence problems due to the cluster size and the relativistic corrections are solved using an expansion of the Dirac Green function for complex energies up to second order in 1/c. The Fermi energy is dealt with via a complex plane integration. Numerical methods used to obtain the semirelativistic Green function in the whole complex plane are explained. We present a calculation of the magnetic circular dichroism at the K edge of bcc iron including the core hole effect. A good agreement is found at high energy. The physical origins of the XMCD spectrum near the edge and far from the edge are analyzed. The influence of the core hole, the possibility of a multiple-scattering expansion, and the relation of XMCD with the spin polarized density of states are discussed. A simple interpretation of XMCD at the K edge is presented in terms of a rigid-band model. \textcopyright{} 1996 The American Physical Society.

Study of 5d magnetism in rare-earth-transition-metal (Fe, Co) intermetallic compounds by magnetic circular X-ray dichroism

Abstract Magnetic circular X-ray dichroism (MCXD) experiments have been performed at the L 2,3 of rare-earth (RE) elements in several Re-transition-metal (Fe, Co) compounds. Experiments at the L 2,3 edges give, in principle, direct information on the 5d magnetic properties of the RE atom which results from the hybridization between the 3d and the 5d electrons. We show in this paper that the use of MCXD experiments at the L 2,3 absorption edges seems to be really complicated when localized 4f electrons are present in the ground state. This unexpected situation is clearly demonstrated by comparing the results obtained on a cerium mixed-valent compound (CeFe 2 ), in which the 4f electrons are highly hybridized with the conduction electrons, and those obtained on a normal trivalent cerium (4f 1 ) compound (CeRu 2 Ge 2 ). Our results suggest that the 4f electrons play an essential role in the description of MCXD at the edges of rare earths.

K-edge x-ray absorption spectra in transition-metal oxides beyond the single-particle approximation: Shake-up many-body effects

Near-edge structures in K-edge x-ray absorption spectra (XAS) are widely investigated to understand the electronic and local structure in materials. The precise interpretation of these spectra with the help of calculations is hence of prime importance, especially for the study of correlated materials which have a complicated electronic structure per se. The single-particle approach, for example, has generally limited itself to the dominant dipolar cross section. It has long been known, however, that effects beyond this approach should be taken into account, due to both the inadequacy of such calculations when compared to experiment and the presence of shakeup many-body satellites in core-level photoemission spectra of correlated materials. This effect should manifest itself in XANES spectra, and the question is first how to account for it theoretically and second how to verify it experimentally. By using state-of-the-art first-principles electronic structure calculations and 1s photoemission measurements, we demonstrate that shakeup many-body effects are present in K-edge XAS dipolar spectra of NiO, CoO, and CuO at all energy scales. We show that shakeup effects can be included in K-edge XAS spectra in a simple way by convoluting the single-particle first-principles calculations including core-hole effects with the 1s photoemission spectra. We thus describe all features appearing in the XAS dipolar cross section of NiO and CoO and obtain a dramatic improvement with respect to the single-particle calculation in CuO. These materials being prototype correlated magnetic oxides, our work points to the presence of shakeup effects in K-edge XANES of most correlated transition-metal compounds and shows how to account for them, paving the way to a precise understanding of their electronic structure.

RARE-EARTH CONTRIBUTIONS TO THE X-RAY MAGNETIC CIRCULAR DICHROISM AT THE CO K EDGE IN RARE-EARTH-COBALT COMPOUNDS INVESTIGATED BY MULTIPLE-SCATTERING CALCULATIONS

The X-ray magnetic circular dichroism (XMCD) has been measured at the Co K edge in Co-hcp and R-Co compounds (R=La, Tb, Dy). The structure of the experimental XMCD spectra in the near-edge region has been observed to be highly sensitive to the magnetic environment of the absorbing site. Calculations of the XMCD have been carried out at the Co K edge in Co metal, LaCo

Use of an asymmetric wiggler to study the magnetic circular x‐ray dichroism of Ni, Ho, and Tb

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X-ray Magnetic and Natural Circular Dichroism from first principles: Calculation of K- and L1-edge spectra

and TbCo

Theory of X-ray natural circular dichroism.

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Magnetic Circular Dichroism at High Magnetic Field and Low Temperature

within the multiple-scattering framework including the spin-orbit coupling. In the three systems, the XMCD spectra in the near-edge region are well reproduced. The possibility to separate and quantitatively estimate the local effects from those due to the neighboring atoms in the XMCD cross section makes possible a more physical understanding of the spectra. The present results emphasize the major role played by the

X-ray absorption spectroscopy of impurities in single-crystals

d

Crystallographic distortion around chromium and iron in rubies and sapphires

states of the Tb ions in the XMCD spectrum at the Co K edge in the TbCo