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Search Results: 1 - 10 of 401290 matches for " Loewenhaupt M. "
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Magnetic field induced Ising axis conversion in Tb0.5Dy0.5Cu2 single crystals
Loewenhaupt M.,Doerr M.,Rotter M.,Reif T.
Brazilian Journal of Physics , 2000,
Abstract: We study the Ising axis conversion in a mixed Tb0.5Dy0.5Cu2 single crystal. Interest is focused on how changes in the exchange interactions due to rare earth substitutions influence the existence of magnetic phases and the critical field values for the Ising axis conversion. From magnetisation measurements we determined the (H - T ) phase diagram for magnetic fields parallel to the easy a-axis and the temperature dependence of the critical field for the Ising axis conversion. Both properties for the mixed crystal follow a simple composition scaling behavior. But in contrast to previous studies on the pure compounds TbCu2 and DyCu2 the changes of magnetic and structural properties at the conversion cannot be recovered completely by thermal treatment. Only a small part (10 % of the sample volume) goes back to the virgin state after warming the sample to 500 K. This behavior is of great interest for further neutron or X-ray diffraction studies of the Ising axis conversion allowing to study the converted phase under routinely used experimental conditions.
Temperature dependence of low-energy phonons in magnetic nonsuperconducting TbNi2B2C
S. Anissimova,A. Kreyssig,O. Stockert,M. Loewenhaupt,D. Reznik
Physics , 2011, DOI: 10.1103/PhysRevB.84.104509
Abstract: We report temperature dependence of low-energy phonons in magnetic nonsuperconducting TbNi2B2C single crystals measured by inelastic neutron scattering. We observed a low-temperature softening and broadening of two phonon branches, qualitatively similar to that previously reported for superconducting RNi2B2C (R= rare earth, Y) compounds. This result suggests that the superconductivity in TbNi2B2C compounds is absent not because of a weak electron-phonon coupling but as a result of pairbreaking due to magnetism.
Evidence for the coexistence of low-dimensional magnetism and long-range order in Ca3CoRhO6
M. Loewenhaupt,W. Schaefer,A. Niazi,E. V. Sampathkumaran
Physics , 2003, DOI: 10.1209/epl/i2003-00542-5
Abstract: We report the results of neutron powder diffraction studies on the spin-chain compound Ca3CoRhO6 in the temperature range 3 to 293 K. Bragg peaks due to magnetic ordering start appearing below about 100 K. The most interesting observation is that there is a diffuse magnetic peak superimposed over the strongest magnetic Bragg peak. The diffuse magnetic intensity is observed below as well above 100 K. This finding provides a new insight into the physics of this compound as though the low-dimensional magnetic interaction coexists with long range magnetic order - a novel situation among quasi one-dimensional oxides.
Magnetic field induced Ising axis conversion in Tb0.5Dy0.5Cu2 single crystals
Loewenhaupt, M.;Doerr, M.;Rotter, M.;Reif, T.;Schneidewind, A.;Hoser, A.;
Brazilian Journal of Physics , 2000, DOI: 10.1590/S0103-97332000000400022
Abstract: we study the ising axis conversion in a mixed tb0.5dy0.5cu2 single crystal. interest is focused on how changes in the exchange interactions due to rare earth substitutions influence the existence of magnetic phases and the critical field values for the ising axis conversion. from magnetisation measurements we determined the (h - t ) phase diagram for magnetic fields parallel to the easy a-axis and the temperature dependence of the critical field for the ising axis conversion. both properties for the mixed crystal follow a simple composition scaling behavior. but in contrast to previous studies on the pure compounds tbcu2 and dycu2 the changes of magnetic and structural properties at the conversion cannot be recovered completely by thermal treatment. only a small part (10 % of the sample volume) goes back to the virgin state after warming the sample to 500 k. this behavior is of great interest for further neutron or x-ray diffraction studies of the ising axis conversion allowing to study the converted phase under routinely used experimental conditions.
Two-dimensional fluctuations at the quantum-critical point of CeCu_{6-x}Au_x
O. Stockert,H. v. L?hneysen,A. Rosch,N. Pyka,M. Loewenhaupt
Physics , 1998, DOI: 10.1103/PhysRevLett.80.5627
Abstract: The heavy-fermion system CeCu_{6-x}Au_x exhibits a quantum critical point at x_c = 0.1 separating nonmagnetic and magnetically ordered ground states. The pronounced non-Fermi-liquid behavior at x_c calls for a search for the relevant quantum critical fluctuations. Systematic measurements of the inelastic neutron scattering cross section S(q,omega) for x = 0.1 reveal rod-like features in the reciprocal ac plane translating to two-dimensional (2d) fluctuations in real space. We find 3d magnetic ordering peaks for x = 0.2 and 0.3 located on these rods which hence can be viewed as 2d precursors of the 3d order.
Magnetic order and transport in the heavy-fermion system CeCu_{6-x}Au_x
H. v. L?hneysen,A. Neubert,A. Schr?der,O. Stockert,U. Tutsch,M. Loewenhaupt,A. Rosch,P. W?lfle
Physics , 1998,
Abstract: We report on extensive elastic neutron scattering to determine the wave vector of the magnetic order in CeCu_{6-x}Au_x single crystals for x > 0.1. For all values of x investigated (0.2, 0.3, 0.5, 1.0) we find long-range incommensurate antiferromagnetic order with an ordering vector Q $\approx$ (0.625 0 0.275) for x=0.2, nearly unchanged for x=0.3, and Q $\approx$ (0.59 0 0) for x=0.5, staying roughly the same for x=1.0. In addition, short-range correlations are observed at x=0.2, reminiscent of those found previously for x=0.1. The ordered magnetic moment is found to increase rapidly for small x, and more slowly for the larger x values. The increase of the specific-heat anomaly at the ordering temperature with x is in qualitative accord with this behavior. Finally, data of the electrical resistivity for current flow along the three crystallographic directions are presented, showing a clear signature of the magnetic order. A theoretical interpretation of the interplay of magnetic order and transport in terms of (i) the partial suppression of the Kondo effect by the staggered magnetization and (ii) the anisotropic band structure induced by the staggered field is shown to account well for the data, provided the ordering vector Q is close to 2 k_F, where k_F is a typical Fermi momentum.
Neutron diffraction on antiferromagnetic ordering in single-crystal BaFe2As2
Y. Su,P. Link,A. Schneidewind,Th. Wolf,P. Adelmann,Y. Xiao,M. Meven,R. Mittal,M. Rotter,D. Johrendt,Th. Brueckel,M. Loewenhaupt
Physics , 2008, DOI: 10.1103/PhysRevB.79.064504
Abstract: Neutron diffraction experiments have been carried out on a Sn-flux grown BaFe2As2 single crystal, the parent compound of the A-122 family of FeAs-based high-Tc superconductors. A tetragonal to orthorhombic structural phase transition and a three dimensional long-range antiferromagnetic ordering of the iron moment, with a unique magnetic propagation wavevector k = (1, 0, 1), have been found to take place at ~90 K. The magnetic moments of iron are aligned along the long a axis in the low temperature orthorhombic phase (Fmmm with b
Novel magnetic behavior of single crystalline Er2PdSi3
K. K. Iyer,P. L. Paulose,E. V. Sampathkumaran,M. Frontzek,A. Kreyssig,M. Doerr,M. Loewenhaupt,I. Mazilu,G. Behr,W. Loeser
Physics , 2004, DOI: 10.1016/j.physb.2004.10.051
Abstract: We report the results of ac and dc magnetic susceptibility (chi) and electrical resistivity (rho) measurements on the single crystals of Er2PdSi3, crystallizing in an AlB2-derived hexagonal structure, for two orientations H//[0001] and H//[2 -1 -1 0]. For H//[0001], there are apparently two magnetic transitions as revealed by the ac chi data, one close to 7 K attributable to antiferromagnetic ordering and the other around 2 K. However, for H // [2 -1 -1 0], we observe additional features above 7 K (near 11 and 23 K) in the plot of low-field chi(T); also, there is no corresponding anomaly in the rho(T) plot. In this respect, the magnetic behavior of this compound is novel, particularly while compared with other members of this series. The features in ac chi respond differently to the application of a small dc magnetic field for the two directions. As far as low temperature (T= 1.8 and 5 K) isothermal magnetization (M) behaviour is concerned, it exhibits meta-magnetic-like features around 2 kOe saturating at high fields for the former orientation, whereas for the latter, there is no saturation even at 120 kOe. The sign of paramagnetic Curie temperature is different for these two directions. Thus, there is a strong anisotropy in the magnetic behavior. However, interestingly, the rho(T) plots are found to be essentially isotropic, with the data revealing possible formation of magnetic superzone formation below 7 K.
Magnetically driven superconductivity in CeCu2Si2
O. Stockert,J. Arndt,E. Faulhaber,C. Geibel,H. S. Jeevan,S. Kirchner,M. Loewenhaupt,K. Schmalzl,W. Schmidt,Q. Si,F. Steglich
Physics , 2012, DOI: 10.1038/NPHYS1852
Abstract: The origin of unconventional superconductivity, including high-temperature and heavy-fermion superconductivity, is still a matter of controversy. Spin excitations instead of phonons are thought to be responsible for the formation of Cooper pairs. Using inelastic neutron scattering, we present the first in-depth study of the magnetic excitation spectrum in momentum and energy space in the superconducting and the normal states of CeCu2Si2. A clear spin excitation gap is observed in the superconducting state. We determine a lowering of the magnetic exchange energy in the superconducting state, in an amount considerably larger than the superconducting condensation energy. Our findings identify the antiferromagnetic excitations as the major driving force for superconducting pairing in this prototypical heavy-fermion compound located near an antiferromagnetic quantum critical point.
Electronic structure and nesting-driven enhancement of the RKKY interaction at the magnetic ordering propagation vector in Gd2PdSi3 and Tb2PdSi3
D. S. Inosov,D. V. Evtushinsky,A. Koitzsch,V. B. Zabolotnyy,S. V. Borisenko,A. A. Kordyuk,M. Frontzek,M. Loewenhaupt,W. Loeser,I. Mazilu,H. Bitterlich,G. Behr,J. -U. Hoffmann,R. Follath,B. Buechner
Physics , 2008, DOI: 10.1103/PhysRevLett.102.046401
Abstract: We present first-time measurements of the Fermi surface and low-energy electronic structure of intermetallic compounds Gd2PdSi3 and Tb2PdSi3 by means of angle-resolved photoelectron spectroscopy (ARPES). Both materials possess a flower-like Fermi surface consisting of an electron barrel at the G point surrounded by spindle-shaped electron pockets originating from the same band. The band bottom of both features lies at 0.5 eV below the Fermi level. From the experimentally measured band structure, we estimate the momentum-dependent RKKY coupling strength and demonstrate that it is peaked at the 1/2 GK wave vector. Comparison with neutron diffraction data from the same crystals shows perfect agreement of this vector with the propagation vector of the low-temperature in-plane magnetic order, thereby demonstrating the decisive role of the Fermi surface geometry in explaining the complex magnetically ordered ground state of ternary rare earth silicides.
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