147 research outputs found
Spin States of Cobalt Ions in the Bulk and on the Surface of LaCoO3 Probed by X-ray Absorption, Emission, and Photoelectron Spectra
We present X-ray photoelectron, Co L2,3 and O K X-ray absorption, as well as Co Kβ1,3 X-ray emission spectroscopy results of studies of the spin states of trivalent cobalt ions in single-crystal cobaltite LaCoO3. We show that at room temperature, in the bulk of a LaCoO3 single crystal, Co3+ ions are in the low-spin state, while high-spin Co2+, high-spin Co3+, low-spin Co3+ , and probably also intermediate-spin Co3+ ions are localated on the surface
Electronic Structure of Transition-Metal Dicyanamides Me[N(CN)] (Me = Mn, Fe, Co, Ni, Cu)
The electronic structure of Me[N(CN)] (Me=Mn, Fe, Co, Ni, Cu)
molecular magnets has been investigated using x-ray emission spectroscopy (XES)
and x-ray photoelectron spectroscopy (XPS) as well as theoretical
density-functional-based methods. Both theory and experiments show that the top
of the valence band is dominated by Me 3d bands, while a strong hybridization
between C 2p and N 2p states determines the valence band electronic structure
away from the top. The 2p contributions from non-equivalent nitrogen sites have
been identified using resonant inelastic x-ray scattering spectroscopy with the
excitation energy tuned near the N 1s threshold. The binding energy of the Me
3d bands and the hybridization between N 2p and Me 3d states both increase in
going across the row from Me = Mn to Me = Cu. Localization of the Cu 3d states
also leads to weak screening of Cu 2p and 3s states, which accounts for shifts
in the core 2p and 3s spectra of the transition metal atoms. Calculations
indicate that the ground-state magnetic ordering, which varies across the
series is largely dependent on the occupation of the metal 3d shell and that
structural differences in the superexchange pathways for different compounds
play a secondary role.Comment: 20 pages, 11 figures, 2 table
Unconventional magnetism of non-uniform distribution of Co in TiO2 nanoparticles
High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), magnetic methods, and density-functional theory (DFT) calculations were applied for the investigations of Co-doped anatase TiO2 nanoparticles (∼20 nm). It was found that high-spin Co2+ ions prefer to occupy the interstitial positions in the TiO2 lattice which are the most energetically favourable in compare to the substitutional those. A quantum mechanical model which operates mainly on two types of Co2+ – Co2+ dimers with different negative exchange interactions and the non-interacting paramagnetic Co2+ ions provides a satisfactorily description of magnetic properties for the TiO2:Co system. © 2020 Elsevier B.V.Russian Foundation for Basic Research. Ministry of Science and Higher Education of the Russian Federatio
ELECTRONIC STRUCTURE OF FeSi
The full set of high-energy spectroscopy measurements including X-ray
photoelectron valence band spectra and soft X-ray emission valence band spectra
of both components of FeSi (Fe K_beta_5, Fe L_alpha, Si K_beta_1,3 and Si
L_2,3) are performed and compared with the results of ab-initio band structure
calculations using the linearized muffin-tin orbital method and linearized
augmented plane wave method.Comment: 11 pages + 3 PostScript figures, RevTex3.0, to be published in
J.Phys.:Cond.Matte
Correlation Effects on Optical Conductivity of FeSi
Effects of electron correlation in FeSi are studied in terms of the two-band
Hubbard model with the density of states obtained from the band calculation.
Using the self-consistent second-order perturbation theory combined with the
local approximation, the correlation effects are investigated on the density of
states and the optical conductivity spectrum, which are found to reproduce the
experiments done by Damascelli et al. semiquantitatively. It is also found that
the peak at the gap edge shifts to lower energy region by correlation effects,
as is seen in the experiments.Comment: 4 pages, 3 figure
Electrical resistivity, magnetism and electronic structure of the intermetallic 3d/4f Laves phase compounds ErNi2Mnx
The non-stoichiometric intermetallic compounds RENi2Mnx (RE = rare earth) with
the cubic MgCu2-type structure display a large variety of magnetic properties which
is due to a complex interplay between the degrees of freedom of the 3d and
4f electrons and their interactions. We performed a comprehensive study of the
electrical resistivity, magnetic properties and the electronic structure of ErNi2Mnx
(x =0, 0.25, 0.5, 0.75, 1, 1.25) compounds by employing a suitable set of complementary
experimental approaches. We find an increase in electrical resistance compared
to ErNi2 upon Mn doping, the residual resistivity ratio decreases with increasing
manganese content. The Curie temperature exhibits a sharp increase to around 50 K
for Mn concentrations x 0.5, whereas the saturation magnetization decreases
with growing Mn content x 0.5. Valence band X-ray photoelectron spectroscopy
reveals an increasing intensity of Mn 3d states near Fermi energy in dependence
of Mn concentration and Curie temperature. Resonant photoelectron spectroscopy
of ErNi2Mn0.75 reveals that the photoemission decay channels dominate the valence
band spectra across the Er N5 and Mn L3 X-ray absorption maxima, whereas the
L3VV Auger dictates the resonant valence band spectra close to and at the Ni L3
X-ray absorption edge
On the strong impact of doping in the triangular antiferromagnet CuCrO2
Electronic band structure calculations using the augmented spherical wave
method have been performed for CuCrO2. For this antiferromagnetic (T_N = 24 K)
semiconductor crystallizing in the delafossite structure, it is found that the
valence band maximum is mainly due to the t_2g orbitals of Cr^3+ and that spin
polarization is predicted with 3 mu_B per Cr^3+. The structural
characterizations of CuCr1-xMgxO2 reveal a very limited range of Mg^2+
substitution for Cr^3+ in this series. As soon as x = 0.02, a maximum of 1% Cr
ions substituted by Mg site is measured in the sample. This result is also
consistent with the detection of Mg spinel impurities from X-ray diffraction
for x = 0.01. This explains the saturation of the Mg^2+ effect upon the
electrical resistivity and thermoelectric power observed for x > 0.01. Such a
very weak solubility limit could also be responsible for the discrepancies
found in the literature. Furthermore, the measurements made under magnetic
field (magnetic susceptibility, electrical resistivity and Seebeck coefficient)
support that the Cr^4+ "holes", created by the Mg^2+ substitution, in the
matrix of high spin Cr^3+ (S = 3/2) are responsible for the transport
properties of these compounds.Comment: 9 pages, 11 figures, more information at
http://www.physik.uni-augsburg.de/~eyert
Electronic Structure and Valence Band Spectra of Bi4Ti3O12
The x-ray photoelectron valence band spectrum and x-ray emission valence-band
spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented
(analyzed in the common energy scale) and interpreted on the basis of a
band-structure calculation for an idealized I4/mmm structure of this material.Comment: 6 pages + 7 PostScript figures, RevTex3.0, to be published in
Phys.Rev.B52 (Oct.95). Figures also available via anonymous ftp at
ftp://ftp.physik.uni-osnabrueck.de/pub/apostnik/BiTiO
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