86 research outputs found
Electronic and Magnetic Properties of ThCo 4 B
ThCo 4 B compound crystallizes in the hexagonal CeCo 4 B type structure. The electronic structure is calculated based on full-potential local--orbital full-relativistic method. The ab initio calculations showed that small magnetic moments (≈ 0.1 µB/atom) are formed on Th and B atoms, antiparallel to the moments on Co atoms equal to 1.55 and 0.43 µ B /atom for Co(2c) and Co(6i), respectively. The densities of states at the Fermi level are equal to 1.3 and 5.4 states/(eV spin f.u.) for spin up and down, respectively. These values are predominated by Co(3d) electrons. Introduction Recently uranium compounds have attracted interest because of many interesting properties such as the Pauli paramagnetism, spin fluctuations, heavy fermions, magnetic ordering, or superconductivity The aim of this paper is to calculate electronic structure of the ThCo 4 B compound based on a spin-polarized ab initio method
Theoretical search for superconductivity in Sc3XB perovskites and weak ferromagnetism in Sc3X (X = Tl, In, Ga, Al)
A possibility for a new family of intermetallic perovskite superconductors
Sc3XB, with X = Tl, In, Ga and Al, is presented as a result of KKR electronic
structure and pseudopotential phonon calculations. The large values of computed
McMillan--Hopfield parameters on scandium suggest appearance of
superconductivity in Sc3XB compounds. On the other hand, the possibility of
weak itinerant ferromagnetic behavior of Sc3X systems is indicated by the small
magnetic moment on Sc atoms in two cases of X =~ l and In. Also the electronic
structure and resulting superconducting parameters for more realistic case of
boron--deficient systems Sc3XB_x are computed using KKR--CPA method, by
replacing boron atom with a vacancy. The comparison of the calculated
McMillan--Hopfield parameters of the Sc3XB series with corresponding values in
MgCNi3 and YRh3B superconductors is given, finding the favorable trends for
superconductivity.Comment: 13 pages, 13 figures. v3 - revise
Electronic properties of CeNiAl4 based on ab initio calculations and XPS measurements
The CeNiAl4 compound crystallizes in an orthorhombic YNiAl4-type structure with a Cmcm space group.
The earlier susceptibility data and X-ray photoelectron spectroscopy (XPS) suggested a localized character of the 4f states in CeNiAl4 with a valence state close to a Ce3 ion. In this work we present a combined theoretical and experimental study of the electronic structure for the Kondo dense system CeNiAl4 based on the XPS data and ab initio calculations. Using the band structure calculations the theoretical XPS valence band spectra are evaluated. Below the Fermi energy the total density of states contains mainly 3d states of Ni hybridized with Ce 4f states
The Electronic and Magnetic Properties of YbxGd1-xNi5 Systems
The intermetallic compounds YbxGd1¡xNi5 crystallize in the hexagonal CaCu5-type structure. Based on
wide ranging SQUID-type magnetometer, it was shown that the saturation magnetization decreases with growing
concentration of ytterbium. The opposite tendency was observed for the Sommerfeld coefficient obtained in the
heat capacity measurements. These results are confirmed using ab initio band structure calculations
Electronic Structure and X-Ray Photoemission Spectra of MPtSn (M = Ti, Zr, Hf)
The electronic structures of the half-Heusler isostructural compounds TiPtSn, ZrPtSn and HfPtSn were
calculated and measured applying the X-ray photoemission spectroscopy. The (Ti, Zr, Hf)PtSn compounds
have gaps between the occupied valence band and the empty conduction band, calculated as about 0.75,
1.12, and 1.09 eV, respectively. The calculations were done by the full-potential local orbitals method in the
framework of the local spin-density approximation and partly also by the full-potential linear mu±n-tin orbitals
method by the LmtART code. Experimental X-ray photoemission spectra were measured using photons of en-
ergy of 1486.6 eV. The experimental and calculated spectra match quite well except a small shift in the energy scale
Intermediate valence of CeNi2Al3 compound and its evidences: Theoretical and experimental approach
We present measurements of magnetic, transport and electronic properties obtained for polycrystalline CeNi2Al3
intermetallic compound. Magnetic susceptibility χ(T) was investigated in the range from 2 to 700 K, and its
behavior is characteristic of a compound with unstable valence, varying between Ce3þ and Ce4þ. In the temperature
range down to 2 K there was no trace of magnetic order, no anomalies in the temperature dependence of
the specific heat were found. The Sommerfeld coefficient extracted from the linear term of the heat capacity
takes a value of γ ¼ 21 mJ/(mol K2). The dependence of S(T) is linear up to about 25 K, which is symptomatic of
a thermopower in the Fermi’s liquid regime.
The structure of satellites in the Ce(3d) electron spectrum obtained by the X-ray photoelectron spectroscopy
(XPS) method indicates that the states of Ce(4f) are of mixed valence character. Analysis of Ce(3d) states based
on Gunnarsson-Sch€onhammer theory shows that the energy of hybridization of Ce(4f) states with a conduction
band is about 78 meV. For more detailed information about electronic states the fully relativistic band structure
was calculated within the density functional theory (DFT) for the first time. Below Fermi’s energy, the density of
states is mainly formed by Ni(3d) states hybridized with Ce(4f) ones
Giant crystal-electric-field effect and complex magnetic behavior in single-crystalline CeRh3Si2
Single-crystalline CeRh3Si2 was investigated by means of x-ray diffraction,
magnetic susceptibility, magnetization, electrical resistivity, and specific
heat measurements carried out in wide temperature and magnetic field ranges.
Moreover, the electronic structure of the compound was studied at room
temperature by cerium core-level x-ray photoemission spectroscopy (XPS). The
physical properties were analyzed in terms of crystalline electric field and
compared with results of ab-initio band structure calculations performed within
the density functional theory approach. The compound was found to crystallize
in the orthorhombic unit cell of the ErRh3Si2 type (space group Imma -- No.74,
Pearson symbol: oI24) with the lattice parameters: a = 7.1330(14) A, b =
9.7340(19) A, and c = 5.6040(11) A. Analysis of the magnetic and XPS data
revealed the presence of well localized magnetic moments of trivalent cerium
ions. All physical properties were found to be highly anisotropic over the
whole temperature range studied, and influenced by exceptionally strong
crystalline electric field with the overall splitting of the 4f1 ground
multiplet exceeding 5700 K. Antiferromagnetic order of the cerium magnetic
moments at TN = 4.70(1)K and their subsequent spin rearrangement at Tt =
4.48(1) K manifest themselves as distinct anomalies in the temperature
characteristics of all investigated physical properties and exhibit complex
evolution in an external magnetic field. A tentative magnetic B-T phase
diagram, constructed for B parallel to the b-axis being the easy magnetization
direction, shows very complex magnetic behavior of CeRh3Si2, similar to that
recently reported for an isostructural compound CeIr3Si2. The electronic band
structure calculations corroborated the antiferromagnetic ordering of the
cerium magnetic moments and well reproduced the experimental XPS valence band
spectrum.Comment: 32 pages, 12 figures, to appear in Physical Review
Spin-polarization-induced structural selectivity in Pd and Pt () compounds
Spin-polarization is known to lead to important {\it magnetic} and {\it
optical} effects in open-shell atoms and elemental solids, but has rarely been
implicated in controlling {\it structural} selectivity in compounds and alloys.
Here we show that spin-polarized electronic structure calculations are crucial
for predicting the correct crystal structures for Pd and Pt
compounds. Spin-polarization leads to (i) stabilization of the structure
over the structure in PtCr, PdCr, and PdMn, (ii) to the
stabilization of the structure over the structure in PdCo
and to (iii) ordering (rather than phase-separation) in PtCo and PdCr.
The results are analyzed in terms of first-principles local spin density
calculations.Comment: 4 pages, REVTEX, 3 eps figures, to appear in PR
A first-principles comparison of the electronic properties of MgC_{y}Ni_{3} and ZnC_{y}Ni_{3} alloys
First-principles, density-functional-based electronic structure calculations
are employed to study the changes in the electronic properties of ZnC_{y}Ni_{3}
and MgC_{y}Ni_{3} using the Korringa-Kohn-Rostoker coherent-potential
approximation method in the atomic sphere approximation (KKR-ASA CPA). As a
function of decreasing C at%, we find a steady decrease in the lattice constant
and bulk modulus in either alloys. However, the pressure derivative of the bulk
modulus displays an opposite trend. Following the Debye model, which relates
the pressure derivative of the bulk modulus with the average phonon frequency
of the crystal, it can thus be argued that ZnCNi_{3} and its disordered alloys
posses a different phonon spectra in comparison to its MgCNi_{3} counterparts.
This is further justified by the marked similarity we find in the electronic
structure properties such as the variation in the density of states and the
Hopfield parameters calculated for these alloys. The effects on the equation of
state parameters and the density of states at the Fermi energy, for partial
replacement of Mg by Zn are also discussed.Comment: 19 pages, 15 figure
Phonon spectrum and soft-mode behavior of MgCNi_3
Temperature dependent inelastic neutron-scattering measurements of the
generalized phonon density-of-states for superconducting MgCNi_3, T_c=8 K, give
evidence for a soft-mode behavior of low-frequency Ni phonon modes. Results are
compared with ab initio density functional calculations which suggest an
incipient lattice instability of the stoichiometric compound with respect to Ni
vibrations orthogonal to the Ni-C bond direction.Comment: 4 pages, 5 figure
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