MnK-edge XANES studies ofLa1−xAxMnO3

Abstract

We present Mn K-edge x-ray absorption near-edge structure ͑XANES͒ data for a number of manganite systems as a function of temperature. The 1s absorption edge for the Ca-substituted samples is very sharp, almost featureless, and shifts uniformly upwards with increasing Ca content. The interpretation of this result is controversial because the lack of structure appears difficult to reconcile with a mixture of Mn ϩ3 and Mn ϩ4 ions or with several different Mn-O bond lengths at high T. We propose a possible solution in terms of covalency and considerable overlap of the Mn p states ͑mostly Mn 4p). The manganite preedge structure is quite similar to that for a large number of other Mn compounds, with two or three small peaks that are ascribed to 1s-3d weakly allowed dipole transitions plus possibly a small quadrupole component. The weak dipole transitions are explained as arising from a hybridization of the Mn 4p state of the excited atom with an odd symmetry combination of Mn 3d states on adjacent Mn atoms. The first preedge peak A 1 has a small shift to higher energy with increasing valence while the next peak A 2 is nearly independent of dopant concentration at 300 K. However, for the colossal magnetoresistance ͑CMR͒ samples the A 2 preedge peak shifts to a lower energy below the ferromagnetic transition temperature T c , resulting in a decrease in the A 2 -A 1 splitting by ϳ0.4 eV. This indicates a change in the higher-energy 3d bands, most likely the minority spin e g , plus some change in covalency. In addition, the amplitudes are temperature dependent for the CMR materials, with the change in A 1 , A 2 correlated with the change in sample magnetization. For the charge ordered ͑CO͒ sample, the analysis suggests that the change in the preedge is produced by a distortion that increases below T CO . We discuss these results in terms of some of the theoretical models that have been proposed and other recent XANES studies.

Delocalization and occupancy effects of 5f orbitals in plutonium intermetallics using L3-edge resonant X-ray emission spectroscopy

“…In Ln materials, the strong localization of the f electrons guarantees a large Up f , thereby enabling a split peak in all known Ln intermediate valence materials at the Ln L 3 edge. In contrast, this splitting condition is typically not met in transition metal systems, and no split peaks are observed (energy shifts are observed instead) [49]. Actinides can potentially exhibit either kind of behavior.…”

Preparation, surface state and band structure studies of SrTi(1−x)Fe(x)O(3−δ) (x=0–1) perovskite-type nano structure by X-ray and ultraviolet photoelectron spectroscopy

“…It was suggested that the intensity of the peak B is proportional to a displacement of Ti atoms from the center of the TiO 6 octahedra [30] but inversely related to the Ti-O bond length. The peak C is a 4p-related "shape resonance" in the continuum part of the spectrum and the peak D is attributed to more delocalized states [34,35]. The XANES spectra show almost no edge shift as a function of x but its intensity and shape change systematically with x.…”

Origin of the Magnetoelectric Coupling Effect inPb(Zr0.2Ti0.8)O3/La0.8Vaz1, Hoffman2, Segal3 et al. 2010Phys. Rev. Lett.330182481View full textAdd to dashboardCite

“…The sample was mounted in an evacuated variable temperature Displex cryostat equipped with a Be dome. In this experiment, we probe the absorption K edge of Mn, corresponding to the allowed electric dipole transition from the 1s core level to unoccupied 4p states [18][19][20]. The light absorption, normalized to the incident photon flux, was measured in the fluorescence mode using the Mn K α line at 5899 eV using a Si drift x-ray detector spectrometer.…”