Max Planck Institute CPfS

Dresden, Germany

Max Planck Institute CPfS

Dresden, Germany

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Severing A.,University of Cologne | Givord F.,CEA Grenoble | Boucherle J.-X.,CEA Grenoble | Willers T.,University of Cologne | And 8 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The magnetic form factor of YbInNi4 has been determined via the flipping ratios R with polarized neutron diffraction, and the scattering function S(Q,ω) was measured in an inelastic neutron scattering experiment. Both experiments were performed with the aim of determining the crystal-field scheme. The magnetic form factor clearly excludes the possibility of a Γ7 doublet as the ground state. The inelastic neutron data exhibit two almost equally strong peaks at 3.2 meV and 4.4 meV which points, in agreement with earlier neutron data, toward a Γ8 quartet ground state. Further possibilities such as a quasiquartet ground state are discussed. © 2011 American Physical Society.


Willers T.,University of Cologne | Hu Z.,University of Cologne | Hu Z.,Max Planck Institute CPfS | Hollmann N.,University of Cologne | And 17 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Linear-polarized soft-x-ray absorption (XAS) and inelastic neutron scattering (INS) experiments have been performed on CeM In5 with M=Rh, Ir, and Co to determine the crystal-field scheme and characteristic Kondo temperatures Tz.ast; for the hybridization between 4f and conduction electrons. The ground-state wave functions are determined from the polarization-dependent soft-XAS data at the cerium M4,5 edge and the crystal-field splittings from INS. The characteristic temperature Tz.ast; has been determined from the line widths of the neutron scattering data. We find that the quasielastic linewidths of the superconducting compounds CeCoIn5 and CeIrIn5 are comparable with the low-energy crystal-field splitting. © 2010 The American Physical Society.


Peyker L.,University of Augsburg | Gold C.,University of Augsburg | Scherer W.,University of Augsburg | Michor H.,Vienna University of Technology | And 7 more authors.
EPL | Year: 2011

Elastic and inelastic neutron scattering experiments were carried out on the heavy-fermion systems CeNi8.6Cu0.4Ge4 and CeNi8CuGe4 to study i) the influences of Ni/Cu substitution on the crystal field parameters and to identify ii) the driving forces of quantum criticality in CeNi9-xCuxGe4. The relevance of competing RKKY and Kondo interactions and changes of the crystal field parameters is discussed. The crystallographic site where the Ni replacement by copper atoms takes place is identified by neutron powder diffraction studies. Furthermore, quasi-elastic and inelastic neutron scattering studies provide detailed information regarding the Kondo properties and the changes of the crystal field parameters resulting from the Ni/Cu replacement. Hence, a reduction of the effective spin degeneracy of the crystal field ground state with increasing Cu concentration is identified as one important control parameter of quantum criticality in CeNi9-xCuxGe 4. The results of these experiments are complemented by measurements of the thermopower. Copyright © EPLA, 2011.


Peyker L.,University of Augsburg | Gold C.,University of Augsburg | Scheidt E.-W.,University of Augsburg | Michor H.,Vienna University of Technology | And 5 more authors.
Journal of Physics: Conference Series | Year: 2010

Substitution of nickel by copper in the heavy fermion system CeNi 9-xCuxGe4 alters the local crystal field environment of the Ce3+-ions. This leads to a quantum phase transition near x ≈ 0.4, which is not only driven by the competition between Kondo effect and RKKY interaction, but also by a reduction of an effectively fourfold to a twofold degenerate crystal field ground state. To study the consequences of a changing crystal field in CeNi8CuGe4 on its Kondo properties, inelastic neutron scattering (INS) experiments were performed. Two well-defined crystal field transitions were observed in the energy-loss spectra at 4K. The crystal field level scheme determined by neutron spectroscopy is compared with results from specific heat measurements. © 2010 IOP Publishing Ltd.


Wu H.-H.,University of Cologne | Wu H.-H.,National Synchrotron Radiation Research Center | Buchholz M.,University of Cologne | Trabant C.,University of Cologne | And 12 more authors.
Nature Communications | Year: 2012

A collective order of spin and charge degrees of freedom into stripes has been predicted to be a possible ground state of hole-doped CuO2 planes, which are the building blocks of high-temperature superconductors. In fact, stripe-like spin and charge order has been observed in various layered cuprate systems. For the prototypical high-temperature superconductor La 2 ? xSrxCuO4, no charge-stripe signal has been found so far, but several indications for a proximity to their formation. Here we report the observation of a pronounced charge-stripe signal in the near surface region of 12-percent doped La2 ? xSrxCuO 4. We conclude that this compound is sufficiently close to charge stripe formation that small perturbations or reduced dimensionality near the surface can stabilize this order. Our finding of different phases in the bulk and near the surface of La2 ? xSrxCuO4 should be relevant for the interpretation of data from surface-sensitive probes, which are widely used for La2 ? xSrxCuO4 and similar systems. © 2012 Macmillan Publishers Limited. All rights reserved.


Gold C.,University of Augsburg | Gross P.,University of Augsburg | Peyker L.,University of Augsburg | Eickerling G.,University of Augsburg | And 6 more authors.
Journal of Physics Condensed Matter | Year: 2012

The pseudo-ternary solid solution CeNi 9Ge 4-xSi x (0≤x≤4) has been investigated by means of x-ray diffraction, magnetic susceptibility, specific heat, electrical resistivity, thermopower and inelastic neutron scattering studies. The isoelectronic substitution of germanium by silicon atoms causes a dramatic change of the relative strength of competing Kondo, RKKY and crystal field (CF) energy scales. The strongest effect is the continuous elevation of the Kondo temperature T K from approximately 3.5K for CeNi 9Ge 4 to about 70K for CeNi 9Si 4. This increase of the Kondo temperature is attended by a change of the CF level scheme of the Ce ions. The interplay of the different energy scales results in an incipient reduction of the ground state degeneracy from an effectively fourfold degenerate non-magnetic Kondo ground state with unusual non-Fermi-liquid features of CeNi 9Ge 4 to a lower one, followed by an increase towards a sixfold, fully degenerate ground state multiplet in CeNi 9Si 4 (T K∼Δ CF). © 2012 IOP Publishing Ltd.


Tanaka A.,Hiroshima University | Chang C.F.,University of Cologne | Chang C.F.,Max Planck Institute CPfS | Buchholz M.,University of Cologne | And 12 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

To elucidate charge and orbital order below the Verwey transition temperature TV∼125 K, a thin layer of magnetite partially detwined by growth on the stepped MgO(001) substrate has been studied by means of soft x-ray diffraction at the Fe L2,3 resonance. The azimuth angle, incident photon polarization, and energy dependence of the ( 0012)c and (001)c reflection intensities have been measured, and analyzed using a configuration-interaction FeO6 cluster model. The azimuth dependence of the (0012)c reflection intensities directly represents the space-group symmetry of the orbital order in the initial state rather than indirectly through the intermediate-state level shifts caused by the order-induced lattice distortions. From the analysis of the ( 0012)c reflection intensities, the orbital order in the t 2g orbitals of B sites below TV is proved to have a large monoclinic deformation with the value of Re[Fxy]/Re[F yz]∼2. This finding contradicts the majority of theories on the Verwey transition so far proposed. We show that the experimentally observed resonance spectra cannot be explained by orbital and charge orders obtained with recent LDA+U and GGA+U band structure calculations but by a complex-number orbital order with excellent agreement. © 2013 American Physical Society.


Tanaka A.,Hiroshima University | Chang C.F.,University of Cologne | Chang C.F.,Max Planck Institute CPfS | Buchholz M.,University of Cologne | And 12 more authors.
Physical Review Letters | Year: 2012

We studied the symmetry of the Fe 3d wave function in magnetite below the Verwey temperature T V with resonant soft-x-ray diffraction. Although the lattice structure of the low-temperature phase of Fe 3O 4 is well described by the pseudo-orthorhombic Pmca with a slight monoclinic P2/c distortion, we find that the 3d wave function does not reflect the Pmca symmetry, and its distortion toward monoclinic symmetry is by far larger than that of the lattice. The result supports a scenario in which the Verwey transition involves the ordering of t 2g orbitals with complex-number coefficients. © 2012 American Physical Society.


Bhattacharyya A.,Rutherford Appleton Laboratory | Bhattacharyya A.,University of Johannesburg | Khalyavin D.D.,Rutherford Appleton Laboratory | Kruger F.,Rutherford Appleton Laboratory | And 7 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

The newly discovered Ising-type ferromagnet CeRu2Al2B exhibits an additional phase transition at TN=14.2 K before entering the ferromagnetic ground state at TC=12.8 K. We clarify the nature of this transition through high resolution neutron diffraction measurements. The data reveal the presence of a longitudinal incommensurate spin-density wave (SDW) in the temperature range of TC


Bhattacharyya A.,Rutherford Appleton Laboratory | Bhattacharyya A.,University of Johannesburg | Ritter C.,Laue Langevin Institute | Adroja D.T.,Rutherford Appleton Laboratory | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

The magnetic state of the tetragonal compound Ce2PdGe3, which crystallizes in the space group P42/mmc, a derivative of the α-ThSi2 structure, has been investigated by magnetic susceptibility, heat capacity, muon spin relaxation (μSR), and neutron diffraction measurements. Heat capacity data indicate two separate magnetic phase transitions at TN1=10.7 K and TN2=2.3 K. The presence of bulk long-range magnetic order is confirmed by our μSR study below 11 K, where a drop of nearly 2/3 in the muon initial asymmetry and a sharp increase in the muon depolarization rate were observed. Neutron powder diffraction reveals that only one out of two Ce sites becomes magnetically ordered with magnetic propagation vector κ=(0) at TN1, adopting an antiferromagnetic arrangement of magnetic moments μCe3+=1.78(1)μB along the c axis. At TN2 the second Ce site orders similarly, following the same magnetic propagation vector κ=(0), showing, however, at the same time a significant ferromagnetic component within the tetragonal basal plane. A second propagation vector, κ=12,0,12, appears concomitantly at TN2 © 2016 American Physical Society.

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