Manfred Neumann - Academia.edu (original) (raw)
Papers by Manfred Neumann
Physical Review B, 1998
The electronic structure of Ce 1Ϫx La x NiSn and Ce 1Ϫx La x RhSb has been studied by photoelectr... more The electronic structure of Ce 1Ϫx La x NiSn and Ce 1Ϫx La x RhSb has been studied by photoelectron spectroscopy. The x-ray excited valence-band spectra are compared with ab initio electronic-structure calculations using the linearized muffin-tin orbital method. The results have been used to compare and contrast the effect of La substitution on the ground state properties of the Kondo insulators CeNiSn and CeRhSb. The Ce 3d x-ray photoemission spectroscopy spectra show evidence for the mixed valence state of Ce in CeRhSb alloys, as also seen for CeNiSn, whereas the spectra for the La substituted ͑Ce,La͒NiSn compounds show only evidence for a pure Ce 3ϩ ground state. We suggest the presence of Kondo-hole states in Ce 1Ϫx La x RhSb.
Physical Review B, 1998
We report on magnetic measurements and electronic structure investigations of the alloyed compoun... more We report on magnetic measurements and electronic structure investigations of the alloyed compounds Zr-Ni-Sn and Ti-Ni-Sn. Both belong to the group of semi-Heusler alloys, and are classified as narrow-gap semiconductors with indirect gaps near 500 meV. Tetravalent ions ͑Zr,Ti͒ are partly replaced by Ce, with a Ce concentration less than 20%. Susceptibility measurements indicate the magnetic ground state of Ce in both Zr-Ni-Sn and Ti-Ni-Sn, and the effective moment is near the trivalent value at Tϭ300 K. The Ce 4 f 1 configuration is well accepted by Ce 3d x-ray photoemission spectra. We compare the x-ray photoemission spectroscopy valence-band spectra for investigated Ce alloys. A very good agreement between the experiments and calculations is obtained. We classify Zr-Ni-Sn and Ti-Ni-Sn as alloys with a strong hybridization influence on the gap formation. The destructive alloying affecting the gap stability seems to have the same origin as in the case of Ce Kondo insulators. ͓S0163-1829͑98͒07115-X͔
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 photoemi... more 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.
Physical Review B, 1997
The electronic structure of CeNi1-xPdxSn has been studied by photoemission spectroscopy. CeNiSn b... more The electronic structure of CeNi1-xPdxSn has been studied by photoemission spectroscopy. CeNiSn belongs to the class of Kondo insulating materials. The gap formed at the Fermi level is strongly suppressed by substituting Pd for Ni. The x-ray photoemission spectroscopy (XPS) valence band spectra can be compared with ab initio electronic-structure calculations using the linearized muffin-tin orbital (LMTO) method. We have
Physical Review B, 2001
The results of investigations of intercalated compounds CrxTiSe2 and CoxTiSe2 by X-ray photoelect... more The results of investigations of intercalated compounds CrxTiSe2 and CoxTiSe2 by X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) are presented. The data obtained are compared with theoretical results of spin-polarized band structure calculations. A good agreement between theoretical and experimental data for the electronic structure of the investigated materials has been observed. The interplay between the M 3d-Ti3d hybridization (M =Cr, Co) and the magnetic moment at the M site is discussed. A 0.9 eV large splitting of the core Cr2p 3/2 level was observed, which reveals a strong exchange magnetic interaction of 3d-2p electrons of Cr. In the case of a strong localization of the Cr3d electrons (for x < 0.25), the broadening of the CrL spectra into the region of the states above the nominal Fermi level was observed and attributed to X-ray re-emission. The measured kinetic properties are in good accordance with spectral investigations and band calculation results.
Physical Review B, 2001
The results of investigations of the Heusler alloys NiMnSb and Co 2 MnSb by magnetic circular dic... more The results of investigations of the Heusler alloys NiMnSb and Co 2 MnSb by magnetic circular dichroism in soft x-ray emission spectroscopy ͑SXEMCD͒ are presented. The data obtained are in a good agreement with theoretical calculations of x-ray emission. A very intense resonant inelastic peak in the Mn L 3 spectra in the region of states above the nominal Fermi level was observed and attributed to x-ray reemission. The interplay between the theoretically predicted half-metallic character of the Mn 3d valence band and the Mn L 2 ,L 3 SXEMCD spectra is discussed.
Physical Review B, 2003
Electronic structure of V15 magnetic molecules (K6[V15As6O42(H2O)]•8H2O) has been studied using L... more Electronic structure of V15 magnetic molecules (K6[V15As6O42(H2O)]•8H2O) has been studied using LSDA+U band structure calculations, and measurements of X-ray photoelectron (valence band, core levels) and X-ray fluorescence spectra (vanadium Kβ5 and L2,3, and oxygen Kα). Experiments confirm that vanadium ions are tetravalent in V15, and their local atomic structure is close to that of CaV3O7. Comparison of experimental data with the results of electronic structure calculations show that the LSDA+U method provides a description of the electronic structure of V15 which agrees well with experiments.
Physical Review B, 1998
The electronic structure and magnetic properties of CeRhSb were investigated by substituting Rh w... more The electronic structure and magnetic properties of CeRhSb were investigated by substituting Rh with 10% of Pd or Co, or Sb with 10% Sn. The 3d and 4d x-ray photoelectron spectroscopy ͑XPS͒ spectra show that CeRhSb and its alloys with Pd and Co are mixed valent. For Sn, the spectra are consistent with trivalence. Analysis of the f 2 weight in the 3d XPS spectra using Gunnarsson-Schönhammer theory suggests a hybridization constant of 140 meV for CeRhSb and about 170 meV for its alloys. Linearized muffin-tin orbital calculations give a pseudo-V-shape gap located at the Fermi level. This classifies these materials as semimetals rather than semiconductors. The location of the pseudogap in CeRhSb varies with the number of valence electrons. We discussed the correlation between the gap at the Fermi level and the number of free electrons, the valence of Ce, and the f-d hybridization. ͓S0163-1829͑98͒00644-4͔
Physical Review B, 2007
We used site-selective and element-specific resonant inelastic x-ray scattering ͑RIXS͒ to study t... more We used site-selective and element-specific resonant inelastic x-ray scattering ͑RIXS͒ to study the electronic structure and the electron interaction effects in the molecular magnet ͓Mn 12 O 12 ͑CH 3 COO͒ 16 ͑H 2 O͒ 4 ͔ • 2CH 3 COOH • 4H 2 O, and compared the experimental data with the results of local spin density approximation +U electron structure calculations which include the on-site Coulomb interactions. We found a good agreement between theory and experiment for the Coulomb repulsion parameter U = 4 eV. In particular, the p-d band separation of 1.8 eV has been found from the RIXS spectra, which is in accordance with the calculations. Similarly, the positions of the peaks in the XPS spectra agree with the calculated densities of p and d states. Using the results of the electronic structure calculations, we determined the intramolecular exchange parameters, and used them for diagonalization of the Mn 12 spin Hamiltonian. The calculated exchanges gave the correct ground state with the total spin S = 10.
Physical Review B, 2006
X-ray absorption, resonant x-ray emission, and x-ray photoelectron spectra of the valence band an... more X-ray absorption, resonant x-ray emission, and x-ray photoelectron spectra of the valence band and core levels have been measured for Li x CoO 2 ͑0.6Յ x Յ 1.0͒. Resonant O K␣ x-ray emission spectra of LiCoO 2 showed localized excitonic states due to a dd transition between unoccupied and occupied Co 3d states. On the basis of measurements of Co 3s x-ray photoelectron and Co 2p and O 1s x-ray absorption spectra it was established that in defective cobaltites the electronic holes are localized mainly in O 2p states. Evidence of phase separation in Li x CoO 2 has been found.
Physical Review B, 2009
We present density functional theory (DFT) calculations and a full set of X-ray spectra (resonant... more We present density functional theory (DFT) calculations and a full set of X-ray spectra (resonant inelastic X-ray scattering and X-ray photoelectron spectra) measurements of single crystal CaFe 2 As 2. The experimental valence band spectra are consistent with our DFT calculations. Both theory and experiment show that the Fe 3dstates dominate the Fermi level and hybridize with Ca 3d-states. The simple shape of Xray photoelectron (XPS) Fe 2p-core level spectrum (without any satellite structure typical for correlated systems) suggests itinerant character of the Fe 3d-electrons. Based on the similarity of the calculated and experimental Fe 3d-states distribution in LaOFeAs and CaFe 2 As 2 we conclude that superconductivity in the FeAs-systems can be described within a minimal model, taking into account only Fe 3d-bands close to the Fermi level.
Physical Review B, 2009
Electronic and magnetic properties of the charge ordered phase of LuFe 2 O 4 are investigated by ... more Electronic and magnetic properties of the charge ordered phase of LuFe 2 O 4 are investigated by means of x-ray spectroscopic and theoretical electronic structure approaches. LuFe 2 O 4 is a compound showing fascinating magnetoelectric coupling via charge ordering. Here, we identify the spin ground state of LuFe 2 O 4 in the charge ordered phase to be a 2:1 ferrimagnetic configuration, ruling out a frustrated magnetic state. An enhanced orbital moment may enhance the magnetoelectric coupling. Furthermore, we determine the densities of states and the corresponding correlation potentials by means of x-ray photoelectron and emission spectroscopies, as well as electronic structure calculations.
Physical Review B, 2009
The electronic structures of SmScO 3 , GdScO 3 , and DyScO 3 are investigated by means of x-ray p... more The electronic structures of SmScO 3 , GdScO 3 , and DyScO 3 are investigated by means of x-ray photoelectron spectroscopy, x-ray emission spectroscopy ͑XES͒, and x-ray absorption spectroscopy ͑XAS͒. A strong hybridization between Sc 3d and O 2p is found, and a contribution of the rare-earth 5d states to this hybridization is not excluded. The band gaps of the compounds are determined by combining XES and XAS measurements. For SmScO 3 , GdScO 3 , and DyScO 3 the band gaps were determined to be 5.6, 5.8, and 5.9 eV, respectively. Magnetization versus temperature measurements reveal antiferromagnetic coupling at 2.96 ͑SmScO 3 ͒, 2.61 ͑GdScO 3 ͒, and 3.10 K ͑DyScO 3 ͒. For DyScO 3 a Rietveld refinement of a 2 K neutrondiffraction data set gives the spin arrangement of Dy in the Pbnm structure ͑Shubnikov group: PbЈnЈmЈ͒.
Physical Review B, 2006
Magnetic and chemical bonding effects in Heusler alloys Ni 2 MnIn, Ni 2 MnSn, and Ni 2 MnSb were ... more Magnetic and chemical bonding effects in Heusler alloys Ni 2 MnIn, Ni 2 MnSn, and Ni 2 MnSb were studied by soft x-ray spectroscopy. Exchange splitting detected in Mn 2p core-level x-ray photoelectron spectra and an increase of the Mn L  / L ␣ intensity ratio in nonresonant x-ray emission spectra show that atomic magnetic moment at Mn is higher than that of pure metal. Spin polarized density of states calculations and comparative analysis of Mn and Ni L ␣ resonant x-ray emission spectra ͑RXES͒ demonstrate that the spin splitting in Mn 3d shell is larger than in Ni 3d shell. The d-d transitions observed in L ␣ RXES of Mn and Ni are suggested to be more intensive for Mn than for Ni valence electrons when initiated by off-resonant excitations. Experimental findings are supported by photoelectron spectra calculations and developed two-step model of resonant x-ray emission. The interplay between Mn L ␣ RXES and calculated magnetic moments of Mn atoms in alloys as a function of the type of Z element is discussed.
physica status solidi (c), 2004
ABSTRACT
physica status solidi (b), 2009
Modern Physics Letters B, 2011
Synthesis, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron s... more Synthesis, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and magnetic measurements at low temperature of Ni metallic clusters covered by NiO , Ce 2 O 3 and CeO 2, obtained from CeNi 5 powder oxidized in air at different temperatures up to 800°C, are reported. The average crystallite size of Ni core and the thickness of NiO oxide formed at the surface increase with temperature due to recrystallization processes, from 34 nm at 300°C to 77 nm at 800°C and from 9 nm to 19 nm, respectively. Ni metallic component was detected both in XPS valence bands and core levels spectra only after sputtering. The hysteresis loop presents a small shift towards negative magnetic fields which confirms the presence of ferromagnetic Ni /antiferromagnetic NiO interfaces.
Magnetic measurements and XPS studies were performed on LaNi5-xAlx, TbNi5-xAlx, DyNi5-xAlx, LaNi5... more Magnetic measurements and XPS studies were performed on LaNi5-xAlx, TbNi5-xAlx, DyNi5-xAlx, LaNi5-xCux and NdNi5-xCux systems. In addition, band structure calculations were also performed. The nickel moments in RNi5 (R=Nd, Tb, Dy) compounds are of ≅ 0.17 µ B and ≅ 0.25 µ B at 2c and 3g sites, respectively. The nickel moments, in low temperature range, decrease when increasing Al or Cu content and are practically nil for x > 1. The 4f-5d-3d exchange interactions were analyzed and the contributions of local 4f-5d and short range 5d-3d exchange interactions to 5d band polarization are estimated. An effective field of the order of (30-40) T is necessary to induce a nickel moment, at 1.7 K. Above the Curie temperatures, the effective nickel moments were determined. The LaNi5-xCux and LaNi5-xAlx systems, show, at T ≤ 10 K, a T2 dependence of the magnetic susceptibilities, while above a characteristic temperature T*, a Curie-Weiss contribution was evidenced. The magnetic behaviour of ni...
Journal of Physics: Condensed Matter, 1998
The electronic structure of 0953-8984/10/28/009/img9 and corresponding x-ray photoemission spectr... more The electronic structure of 0953-8984/10/28/009/img9 and corresponding x-ray photoemission spectra (XPS) are presented. The band structure is calculated by the spin-polarized tight binding linear muffin tin orbital (TB LMTO) method. The XPS valence bands are compared with the calculated electronic density of states. 0953-8984/10/28/009/img9 is ferromagnetic with a calculated total magnetic moment 0953-8984/10/28/009/img11 and the local magnetic moments on Nd and Co atoms are parallel.
Physical Review B, 1998
The electronic structure of Ce 1Ϫx La x NiSn and Ce 1Ϫx La x RhSb has been studied by photoelectr... more The electronic structure of Ce 1Ϫx La x NiSn and Ce 1Ϫx La x RhSb has been studied by photoelectron spectroscopy. The x-ray excited valence-band spectra are compared with ab initio electronic-structure calculations using the linearized muffin-tin orbital method. The results have been used to compare and contrast the effect of La substitution on the ground state properties of the Kondo insulators CeNiSn and CeRhSb. The Ce 3d x-ray photoemission spectroscopy spectra show evidence for the mixed valence state of Ce in CeRhSb alloys, as also seen for CeNiSn, whereas the spectra for the La substituted ͑Ce,La͒NiSn compounds show only evidence for a pure Ce 3ϩ ground state. We suggest the presence of Kondo-hole states in Ce 1Ϫx La x RhSb.
Physical Review B, 1998
We report on magnetic measurements and electronic structure investigations of the alloyed compoun... more We report on magnetic measurements and electronic structure investigations of the alloyed compounds Zr-Ni-Sn and Ti-Ni-Sn. Both belong to the group of semi-Heusler alloys, and are classified as narrow-gap semiconductors with indirect gaps near 500 meV. Tetravalent ions ͑Zr,Ti͒ are partly replaced by Ce, with a Ce concentration less than 20%. Susceptibility measurements indicate the magnetic ground state of Ce in both Zr-Ni-Sn and Ti-Ni-Sn, and the effective moment is near the trivalent value at Tϭ300 K. The Ce 4 f 1 configuration is well accepted by Ce 3d x-ray photoemission spectra. We compare the x-ray photoemission spectroscopy valence-band spectra for investigated Ce alloys. A very good agreement between the experiments and calculations is obtained. We classify Zr-Ni-Sn and Ti-Ni-Sn as alloys with a strong hybridization influence on the gap formation. The destructive alloying affecting the gap stability seems to have the same origin as in the case of Ce Kondo insulators. ͓S0163-1829͑98͒07115-X͔
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 photoemi... more 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.
Physical Review B, 1997
The electronic structure of CeNi1-xPdxSn has been studied by photoemission spectroscopy. CeNiSn b... more The electronic structure of CeNi1-xPdxSn has been studied by photoemission spectroscopy. CeNiSn belongs to the class of Kondo insulating materials. The gap formed at the Fermi level is strongly suppressed by substituting Pd for Ni. The x-ray photoemission spectroscopy (XPS) valence band spectra can be compared with ab initio electronic-structure calculations using the linearized muffin-tin orbital (LMTO) method. We have
Physical Review B, 2001
The results of investigations of intercalated compounds CrxTiSe2 and CoxTiSe2 by X-ray photoelect... more The results of investigations of intercalated compounds CrxTiSe2 and CoxTiSe2 by X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) are presented. The data obtained are compared with theoretical results of spin-polarized band structure calculations. A good agreement between theoretical and experimental data for the electronic structure of the investigated materials has been observed. The interplay between the M 3d-Ti3d hybridization (M =Cr, Co) and the magnetic moment at the M site is discussed. A 0.9 eV large splitting of the core Cr2p 3/2 level was observed, which reveals a strong exchange magnetic interaction of 3d-2p electrons of Cr. In the case of a strong localization of the Cr3d electrons (for x < 0.25), the broadening of the CrL spectra into the region of the states above the nominal Fermi level was observed and attributed to X-ray re-emission. The measured kinetic properties are in good accordance with spectral investigations and band calculation results.
Physical Review B, 2001
The results of investigations of the Heusler alloys NiMnSb and Co 2 MnSb by magnetic circular dic... more The results of investigations of the Heusler alloys NiMnSb and Co 2 MnSb by magnetic circular dichroism in soft x-ray emission spectroscopy ͑SXEMCD͒ are presented. The data obtained are in a good agreement with theoretical calculations of x-ray emission. A very intense resonant inelastic peak in the Mn L 3 spectra in the region of states above the nominal Fermi level was observed and attributed to x-ray reemission. The interplay between the theoretically predicted half-metallic character of the Mn 3d valence band and the Mn L 2 ,L 3 SXEMCD spectra is discussed.
Physical Review B, 2003
Electronic structure of V15 magnetic molecules (K6[V15As6O42(H2O)]•8H2O) has been studied using L... more Electronic structure of V15 magnetic molecules (K6[V15As6O42(H2O)]•8H2O) has been studied using LSDA+U band structure calculations, and measurements of X-ray photoelectron (valence band, core levels) and X-ray fluorescence spectra (vanadium Kβ5 and L2,3, and oxygen Kα). Experiments confirm that vanadium ions are tetravalent in V15, and their local atomic structure is close to that of CaV3O7. Comparison of experimental data with the results of electronic structure calculations show that the LSDA+U method provides a description of the electronic structure of V15 which agrees well with experiments.
Physical Review B, 1998
The electronic structure and magnetic properties of CeRhSb were investigated by substituting Rh w... more The electronic structure and magnetic properties of CeRhSb were investigated by substituting Rh with 10% of Pd or Co, or Sb with 10% Sn. The 3d and 4d x-ray photoelectron spectroscopy ͑XPS͒ spectra show that CeRhSb and its alloys with Pd and Co are mixed valent. For Sn, the spectra are consistent with trivalence. Analysis of the f 2 weight in the 3d XPS spectra using Gunnarsson-Schönhammer theory suggests a hybridization constant of 140 meV for CeRhSb and about 170 meV for its alloys. Linearized muffin-tin orbital calculations give a pseudo-V-shape gap located at the Fermi level. This classifies these materials as semimetals rather than semiconductors. The location of the pseudogap in CeRhSb varies with the number of valence electrons. We discussed the correlation between the gap at the Fermi level and the number of free electrons, the valence of Ce, and the f-d hybridization. ͓S0163-1829͑98͒00644-4͔
Physical Review B, 2007
We used site-selective and element-specific resonant inelastic x-ray scattering ͑RIXS͒ to study t... more We used site-selective and element-specific resonant inelastic x-ray scattering ͑RIXS͒ to study the electronic structure and the electron interaction effects in the molecular magnet ͓Mn 12 O 12 ͑CH 3 COO͒ 16 ͑H 2 O͒ 4 ͔ • 2CH 3 COOH • 4H 2 O, and compared the experimental data with the results of local spin density approximation +U electron structure calculations which include the on-site Coulomb interactions. We found a good agreement between theory and experiment for the Coulomb repulsion parameter U = 4 eV. In particular, the p-d band separation of 1.8 eV has been found from the RIXS spectra, which is in accordance with the calculations. Similarly, the positions of the peaks in the XPS spectra agree with the calculated densities of p and d states. Using the results of the electronic structure calculations, we determined the intramolecular exchange parameters, and used them for diagonalization of the Mn 12 spin Hamiltonian. The calculated exchanges gave the correct ground state with the total spin S = 10.
Physical Review B, 2006
X-ray absorption, resonant x-ray emission, and x-ray photoelectron spectra of the valence band an... more X-ray absorption, resonant x-ray emission, and x-ray photoelectron spectra of the valence band and core levels have been measured for Li x CoO 2 ͑0.6Յ x Յ 1.0͒. Resonant O K␣ x-ray emission spectra of LiCoO 2 showed localized excitonic states due to a dd transition between unoccupied and occupied Co 3d states. On the basis of measurements of Co 3s x-ray photoelectron and Co 2p and O 1s x-ray absorption spectra it was established that in defective cobaltites the electronic holes are localized mainly in O 2p states. Evidence of phase separation in Li x CoO 2 has been found.
Physical Review B, 2009
We present density functional theory (DFT) calculations and a full set of X-ray spectra (resonant... more We present density functional theory (DFT) calculations and a full set of X-ray spectra (resonant inelastic X-ray scattering and X-ray photoelectron spectra) measurements of single crystal CaFe 2 As 2. The experimental valence band spectra are consistent with our DFT calculations. Both theory and experiment show that the Fe 3dstates dominate the Fermi level and hybridize with Ca 3d-states. The simple shape of Xray photoelectron (XPS) Fe 2p-core level spectrum (without any satellite structure typical for correlated systems) suggests itinerant character of the Fe 3d-electrons. Based on the similarity of the calculated and experimental Fe 3d-states distribution in LaOFeAs and CaFe 2 As 2 we conclude that superconductivity in the FeAs-systems can be described within a minimal model, taking into account only Fe 3d-bands close to the Fermi level.
Physical Review B, 2009
Electronic and magnetic properties of the charge ordered phase of LuFe 2 O 4 are investigated by ... more Electronic and magnetic properties of the charge ordered phase of LuFe 2 O 4 are investigated by means of x-ray spectroscopic and theoretical electronic structure approaches. LuFe 2 O 4 is a compound showing fascinating magnetoelectric coupling via charge ordering. Here, we identify the spin ground state of LuFe 2 O 4 in the charge ordered phase to be a 2:1 ferrimagnetic configuration, ruling out a frustrated magnetic state. An enhanced orbital moment may enhance the magnetoelectric coupling. Furthermore, we determine the densities of states and the corresponding correlation potentials by means of x-ray photoelectron and emission spectroscopies, as well as electronic structure calculations.
Physical Review B, 2009
The electronic structures of SmScO 3 , GdScO 3 , and DyScO 3 are investigated by means of x-ray p... more The electronic structures of SmScO 3 , GdScO 3 , and DyScO 3 are investigated by means of x-ray photoelectron spectroscopy, x-ray emission spectroscopy ͑XES͒, and x-ray absorption spectroscopy ͑XAS͒. A strong hybridization between Sc 3d and O 2p is found, and a contribution of the rare-earth 5d states to this hybridization is not excluded. The band gaps of the compounds are determined by combining XES and XAS measurements. For SmScO 3 , GdScO 3 , and DyScO 3 the band gaps were determined to be 5.6, 5.8, and 5.9 eV, respectively. Magnetization versus temperature measurements reveal antiferromagnetic coupling at 2.96 ͑SmScO 3 ͒, 2.61 ͑GdScO 3 ͒, and 3.10 K ͑DyScO 3 ͒. For DyScO 3 a Rietveld refinement of a 2 K neutrondiffraction data set gives the spin arrangement of Dy in the Pbnm structure ͑Shubnikov group: PbЈnЈmЈ͒.
Physical Review B, 2006
Magnetic and chemical bonding effects in Heusler alloys Ni 2 MnIn, Ni 2 MnSn, and Ni 2 MnSb were ... more Magnetic and chemical bonding effects in Heusler alloys Ni 2 MnIn, Ni 2 MnSn, and Ni 2 MnSb were studied by soft x-ray spectroscopy. Exchange splitting detected in Mn 2p core-level x-ray photoelectron spectra and an increase of the Mn L  / L ␣ intensity ratio in nonresonant x-ray emission spectra show that atomic magnetic moment at Mn is higher than that of pure metal. Spin polarized density of states calculations and comparative analysis of Mn and Ni L ␣ resonant x-ray emission spectra ͑RXES͒ demonstrate that the spin splitting in Mn 3d shell is larger than in Ni 3d shell. The d-d transitions observed in L ␣ RXES of Mn and Ni are suggested to be more intensive for Mn than for Ni valence electrons when initiated by off-resonant excitations. Experimental findings are supported by photoelectron spectra calculations and developed two-step model of resonant x-ray emission. The interplay between Mn L ␣ RXES and calculated magnetic moments of Mn atoms in alloys as a function of the type of Z element is discussed.
physica status solidi (c), 2004
ABSTRACT
physica status solidi (b), 2009
Modern Physics Letters B, 2011
Synthesis, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron s... more Synthesis, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and magnetic measurements at low temperature of Ni metallic clusters covered by NiO , Ce 2 O 3 and CeO 2, obtained from CeNi 5 powder oxidized in air at different temperatures up to 800°C, are reported. The average crystallite size of Ni core and the thickness of NiO oxide formed at the surface increase with temperature due to recrystallization processes, from 34 nm at 300°C to 77 nm at 800°C and from 9 nm to 19 nm, respectively. Ni metallic component was detected both in XPS valence bands and core levels spectra only after sputtering. The hysteresis loop presents a small shift towards negative magnetic fields which confirms the presence of ferromagnetic Ni /antiferromagnetic NiO interfaces.
Magnetic measurements and XPS studies were performed on LaNi5-xAlx, TbNi5-xAlx, DyNi5-xAlx, LaNi5... more Magnetic measurements and XPS studies were performed on LaNi5-xAlx, TbNi5-xAlx, DyNi5-xAlx, LaNi5-xCux and NdNi5-xCux systems. In addition, band structure calculations were also performed. The nickel moments in RNi5 (R=Nd, Tb, Dy) compounds are of ≅ 0.17 µ B and ≅ 0.25 µ B at 2c and 3g sites, respectively. The nickel moments, in low temperature range, decrease when increasing Al or Cu content and are practically nil for x > 1. The 4f-5d-3d exchange interactions were analyzed and the contributions of local 4f-5d and short range 5d-3d exchange interactions to 5d band polarization are estimated. An effective field of the order of (30-40) T is necessary to induce a nickel moment, at 1.7 K. Above the Curie temperatures, the effective nickel moments were determined. The LaNi5-xCux and LaNi5-xAlx systems, show, at T ≤ 10 K, a T2 dependence of the magnetic susceptibilities, while above a characteristic temperature T*, a Curie-Weiss contribution was evidenced. The magnetic behaviour of ni...
Journal of Physics: Condensed Matter, 1998
The electronic structure of 0953-8984/10/28/009/img9 and corresponding x-ray photoemission spectr... more The electronic structure of 0953-8984/10/28/009/img9 and corresponding x-ray photoemission spectra (XPS) are presented. The band structure is calculated by the spin-polarized tight binding linear muffin tin orbital (TB LMTO) method. The XPS valence bands are compared with the calculated electronic density of states. 0953-8984/10/28/009/img9 is ferromagnetic with a calculated total magnetic moment 0953-8984/10/28/009/img11 and the local magnetic moments on Nd and Co atoms are parallel.