Influence of the Kondo-hole impurities on the electronic structure of CeNiSn and CeRhSb (original) (raw)
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Journal of Physics: Condensed Matter, 2007
We report on the electronic structure and magnetic properties of the Kondo lattice system CeRhSn 2 and of the reference compound LaRhSn 2. The Ce 3d and 4d x-ray photoemission spectroscopy (XPS) data point to a stable configuration of the Ce 4f shell in CeRhSn 2. The ac magnetic susceptibility measurements reveal two magnetic transitions for CeRhSn 2 at temperatures T C1 ≈ 4 K and T C2 ≈ 3 K. The temperature dependences of the ac susceptibility show also broad maxima at about 17 and 15 K for CeRhSn 2 and LaRhSn 2 , respectively. Such features hint at spin fluctuations on Rh atoms. To get detailed insight into the electronic structure of both CeRhSn 2 and LaRhSn 2 we perform ab initio band structure calculations within the local (spin) density approximation (L(S)DA) and using the LSDA + U approach to account for the strong Coulomb interactions within the Ce 4f shell. The LSDA + U approximation gives qualitatively the correct physical picture of Ce 3+ in CeRhSn 2. The reliability of the theoretical results is confirmed by the comparison of the calculated XPS valence band spectra with experimental data. A Fermi surface analysis shows that there are some parallel sections of the sheets, which could generate 'nesting' instabilities. These nesting features might be responsible for the spin fluctuations suggested by the ac susceptibility measurements.
Effect of alloying on the electronic structure in CeNiSn
Physical Review B, 1996
The electronic structure of CeNi 1Ϫx Cu x Sn system and Ce 0.9 Zr 0.1 NiSn is studied by photoemission spectroscopy. CeNiSn is a rare example of a valence-fluctuating Ce compound with a small gap at the Fermi energy. The gap is strongly suppressed by substituting either Cu for Ni or Zr for Ce. The XPS valence-band spectra are compared with ab initio band structure calculations, using the linearized muffin-tin orbital method. For CeNiSn a small indirect energy gap and a very low density of states at the Fermi level is found. The substitution of Ni by Cu leads to a higher density of states at Fermi energy, whereas for the substitution of Ce by even 10% Zr, the changes of the density of states at ⑀ F are clearly visible. A strong hybridization of the f orbitals with a conduction band is characteristic for all of the investigated compounds. We report the Ce 3d XPS spectra of CeNi 1Ϫx Cu x Sn and Ce 0.9 Zr 0.1 NiSn. Applying the Gunnarsson-Schönhammer model the coupling energy ⌬ between the f levels and the conduction states is about 115 meV. The number of 4 f electrons n f is 0.95 for CeNiSn. With increasing Cu concentration, n f is close to 1. The magnetic susceptibility of CeNi 1Ϫx Cu x Sn and Ce 0.9 Zr 0.1 NiSn is measured in magnetic fields from 50 Oe up to 5 T.
Electronic structure of CexSny compounds
Journal of Alloys and Compounds, 2005
We present the structural properties, the electronic structure, and the 3d and 4d X-ray photoemission (XPS) spectra for eight cerium stannides of the Ce x Sn y -type. Previous magnetic investigations showed that Ce in CeSn 3 , Ce 2 Sn 5 and Ce 3 Sn 7 has a mixed valence whereas Ce 5 Sn 3 and Ce 3 Sn are known as heavy fermions. The 3d and 4d XPS spectra obtained for Ce x Sn y series indicate a mixed valence of Ce. The 3d XPS spectra and LMTO calculations indicate a strong hybridization energy ∆ of the f-orbitals with conduction band. Both the quantity: hybridization energy ∆, as well as the valence of Ce, depend on the number of Ce atoms and give evidence, that the type of crystallographic structure and the number of nearest Ce-neighbors decide about the ground state properties of these compounds.
Electronic properties of isostructural intermetallics of Ce
Journal of Magnetism and Magnetic Materials, 1992
We present self-consistent FLAPW-LSD electronic structure calculations of ferromagnetic CeAg, CeCd and CeZn, including the spin-orbit interaction in the spin-polarised formalism. The incomplete Ce 4f-state polarisation indicates the presence of Anderson hybridisation with conduction bands. The calculated magnetic moments are compared to previous theoretical and experimental results, for the three compounds.
Magnetic, electronic and Shubnikov-de Haas investigation of the dense Kondo system CeAgSb2
Of the dense Kondo materials in the class CeTSb2 (where T = Au, Ag, Ni, Cu, or Pd), CeAgSb2 is special due to its complex magnetic ground state, which exhibits both ferro- and anti-ferromagnetic character below an ordering temperature TO ~ 9.8 K. To further elucidate a description this magnetic ground state, we have carried out a systematic study of single crystalline CeAgSb2 by magnetic, electrical magneto-transport, and Shubnikov-de Haas (SdH) studies over a broad range of temperature and magnetic field. We have constructed the magnetic phase diagram based solely on magnetoresistance data. Here, depending on the orientation of the magnetic field H, either ferromagnetic or antiferromagnetic ordering occurs below TO. The resistivity of this compound below TO does not follow a simple Fermi liquid behavior, but requires an additional contribution from conduction electron scattering from boson excitations with an energy gap, D. At zero field the temperature dependent resistivity below ...
Importance of Co 3d electron correlation in a Ce-based Kondo lattice, Ce(2)CoSi(3
2009
We study the role of electron correlations among Co 3d electrons contributing to the conduction band of a Kondo lattice compound, Ce2CoSi3, using high resolution photoemission spectroscopy and ab initio band structure calculations. Experimental results reveal signature of Ce 4f states derived Kondo resonance feature at the Fermi level and dominance of Co 3d contributions at higher binding energies in the valence band. The line shape of the experimental Co 3d band is found to be significantly different from that obtained from the band structure calculations within the local density approximations. Consideration of electron-electron Coulomb repulsion among Co 3d electrons leads to a better representation of experimental results. The correlation strength among Co 3d electrons is found to be about 3 eV. Signature of electron correlation induced satellite feature is also observed in the Co 2p core level spectrum. Thus, these results demonstrate the importance of the electron correlation among conduction electrons to derive the microscopic description of such Kondo systems.
Electronic structure and thermodynamic properties of Ce3Rh4Sn13and La3Rh4Sn13
Journal of Physics: Condensed Matter, 2008
We report on the electronic structure and basic thermodynamic properties of Ce 3 Rh 4 Sn 13 and of the reference compound La 3 Rh 4 Sn 13. XPS core-level spectra revealed a stable trivalent configuration of the Ce atoms in Ce 3 Rh 4 Sn 13 , consistent with magnetic susceptibility data. Band structure calculations within the LSDA + U approximation yield the qualitatively correct description of Ce in a trivalent state. The reliability of the theoretical results has been confirmed by a comparison of the calculated XPS valence band spectra with experimental data. The calculated densities of states as well as the rare-earth (RE) 3d XPS spectra point to a weak hybridization between the RE 4f shell and the conduction band states. The band structure calculations result in a magnetic ground state for Ce 3 Rh 4 Sn 13. Previous analysis pointed to the partial occupancy of the 2a site by Sn atoms. The charge density analysis reveals the dominant metallic character of the chemical bonding at the 2a atomic position. Simulation of vacancies at the 2a site using the virtual crystal approximation (VCA) indicate that the magnetic properties of Ce 3 Rh 4 Sn 13 strongly depend on the Sn content, which could explain the discrepancy in magnetic properties between different Ce 3 Rh 4 Sn 13 samples.
Physical Review B, 2010
We report measurements of inelastic neutron scattering, magnetic susceptibility, magnetization, and the magnetic field dependence of the specific heat for the heavy Fermion compounds Ce3In and Ce3Sn. The neutron scattering results show that the excited crystal field levels have energies E1 = 13.2 meV, E2 = 44.8 meV for Ce3In and E1 = 18.5 meV, E2 = 36.1 meV for Ce3Sn. The Kondo temperature deduced from the quasielastic linewidth is 17 K for Ce3In and 40 K for Ce3Sn. The low temperature behavior of the specific heat, magnetization, and susceptibility can not be welldescribed by J=1/2 Kondo physics alone, but require calculations that include contributions from the Kondo effect, broadened crystal fields, and ferromagnetic correlations, all of which are known to be important in these compounds. We find that in Ce3In the ferromagnetic fluctuation makes a 10-15 % contribution to the ground state doublet entropy and magnetization. The large specific heat coefficient γ in this heavy fermion system thus arises more from the ferromagnetic correlations than from the Kondo behavior.
Electronic structure of CeRhX (X = Sn, In)
European Physical Journal B, 2009
Electronic structure of the compounds CeRhIn and CeRhSn have been studied by the X-ray photoemission spectroscopy (XPS) and ab initio band structure calculations. CeRhSn shows the non-Fermi liquid characteristics at low temperatures, while CeRhIn exhibits a Fermi-liquid ground state. At ambient temperature the XPS data reveal an intermediate valence state of Ce ions in both systems. The Ce corelevel XPS spectra are very similar and indicate the strong coupling of the Ce 4f and the conduction band states (Δ ≈ 100 meV). The valence band spectra we interpret with the help of ab initio calculations as well as using the results for the reference compounds LaRhIn and LaRhSn. The comparative analysis of the theoretical band structures and charge density plots reveal the changes in chemical bonding and the hybridization between the Ce 4f and the other valence states introduced by the replacement of In by Sn atoms. The more covalent character of the chemical bonding in the stannides is in line with the smaller thermal expansion. Finally, for CeRhIn we found a typical temperature dependence of the crystal lattice, while CeRhSn shows distinct anomaly at about 120 K, presumably related to the change in planar Ce-Rh bonds.