共查询到20条相似文献,搜索用时 15 毫秒
1.
C. Buschhaus R. Desquiotz K. Eichhorn M. Hofmann K. Hümmer V. Illich M. Kelemen S. Tarragona Auga T. Wokrina A. Zitsch E. Dormann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):57-66
Crystal growth and X-ray structural analysis are reported for the new quasi-one-dimensional organic conductor perylene hexafluoroantimonate.
Due to deviation from exact 4:3 stoichiometry and anion-chain disorder the three-dimensional Peierls transition is suppressed
to temperatures below 30 K in spite of a molecular field transition temperature of 330 K. Anisotropy of the microwave conductivity
exceeds 3000:1 at room temperature. Curie paramagnetic defects with comparatively small electron spin resonance line width
predominate at low temperature. Thermally activated paramagnetic defects, giving rise to pronounced Overhauser shift, are
separated in the 30-100 K range. They are explained by neutral Perylene intra-stack defects, whose concentration can be reduced
by both aging and annealing. The angular and temperature dependence of the conduction electron spin resonance line is analysed
in detail, exhibiting the influence of intra-stack dipole interaction growing with temperature. Restricted diffusion of the
conduction electron spins with diffusion coefficient of about 6 cm2/s parallel to the stacking direction is detected by fixed gradient pulsed electron spin resonance at room temperature.
Received 17 July 1998 相似文献
2.
R. Desquiotz M. Hofmann E. Dormann 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):403-410
Conduction electron properties of the quasi-one-dimensional conductors and (PE = perylene, THF = tetrahydrofurane) were investigated by measuring magnetic susceptibility and microwave conductivity
in the temperature range from 10 K to 300 K. For quantitative analysis of the measurements a microscopic model was developed.
Received 23 November 1999 相似文献
3.
Electron spin resonance and magnetic susceptibility suggest superconductivity in Na doped WO3samples
A. Shengelaya S. Reich Y. Tsabba K.A. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):13-15
In WO3 doped with Na (WO3:Na) an Electron Spin Resonance (ESR) signal with unresolved fine and/or hyperfine structure is detected and used as a probe
for the state of the carriers. Using the saturation method we determined the spin-lattice relaxation rate 1/
T
1
of these paramagnetic centers. Upon cooling below 100 K, 1/
T
1
decreases markedly, as known to occur in NMR when a gap opens in the superconducting state. At low temperatures, 1/
T
1
quantitatively follows BCS behavior with a gap K or 2 . The magnetic susceptibility exhibits a strong difference between magnetic-field cooled and zero-field cooled regimes below
which also supports a so far unknown superconducting phase resulting from Na doping.
Received 14 April 1999 and Received in final form 6 September 1999 相似文献
4.
J. Choukroun V.A. Pashchenko Y. Ksari J.Y. Henry F. Mila P. Millet P. Monod A. Stepanov J. Dumas R. Buder 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):655-659
The magnetic susceptibility and the electron spin resonance in the X-band of the transition metal oxide compound MgVO3 are reported. We show that this compound, made of weakly coupled infinite chains of VO5 pyramids, behaves as a S
=1/2 one-dimensional Heisenberg antiferromagnet. From the ESR and magnetic experiments we deduce the Néel temperature K, the in-chain coupling constant K and the g-factor values g
x
=
g
z
=1.972(2), g
y
=1.946(1) for V4+ ions in MgVO3.
Received 14 July 1999 相似文献
5.
K. Ghosh A. Dutta J.K. Bhattacharjee 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):219-221
We calculate using diagrammatic perturbation theory in the two-loop approximation, the specific heat exponent for the classical N-vector model in a random external field for spatial dimension (D) lying between four and six. The calculation supports the modified hyperscaling , where is the correlation length exponent.
Received: 18 March 1998 / Revised: 17 April 1998 / Accepted: 21 April 1998 相似文献
6.
A.V. Prokofiev F. Büllesfeld W. Assmus H. Schwenk D. Wichert U. Löw B. Lüthi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):313-316
Experimental results on magnetic resonance (ESR) and magnetic susceptibility are given for single crystalline (VO)2P2O7. The crystal growth procedure is briefly discussed. The susceptibility is interpreted numerically using a model with alternating
spin chains. We determine J
=51 K and . Furthermore we find a spin gap of meV from our ESR measurements. Using elastic constants no indication of a phase transition forcing the dimerization is seen
below 300 K.
Received: 22 December 1997 / Accepted: 17 March 1998 相似文献
7.
N. Petit F. Gervais P. Buvat P. Hourquebie P. Topart 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):367-372
The reflectivity spectrum of a polyaniline CSA-doped in presence of m-cresol has been measured over the wide wavenumber range
of 15- 9 000 cm
-1 (0.002-1.1 eV) at room temperature. Experimental data compare well with similar experiments performed by another group. The
conductivity spectrum of this conducting polymer has been deduced from the reflectivity spectrum by means of two methods,
Kramers-Kronig transformation and best fit of an “extended Drude” model to the reflectivity spectrum. Whereas the deviation
from Drude behavior was interpreted in terms of Anderson localization or by inhomogeneous disorder by other groups, it is
shown here that a different model developed for conducting oxides that also exhibit non-Drude behavior, applies very well
to this example of conducting polymer.
Received 11 February 1999 and Received in final form 26 April 1999 相似文献
8.
N.V. Baranov E. Bauer R. Hauser A. Galatanu Y. Aoki H. Sato 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):67-72
Electrical resistivity and calorimetric measurements on Dy
3
Coshow that below the Néel temperature (T
N
=44 K) the non-collinear antiferromagnetic structure exhibits field-induced magnetic phase transitions of a first-order type
along all principal axes, accompanied by a strongly anisotropic giant magnetoresistance and by a change of the Sommerfeld
coefficient of the specific heat. Quantum tunnelling of the magnetization appears to be possible for T
< 0.6 K.
Received 15 July 1999 and Received in final form 6 December 1999 相似文献
9.
F. Gervais N. Petit C. Popon P. Buvat 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):47-52
The reflectivity spectrum of a polyaniline CSA-doped in presence of m-cresol has been measured over the wide wavenumber range
25-15,000 cm-1 (0.003-1.9 eV) for three different doping levels. Since spectra cannot be fitted correctly with the conventional Drude model,
several extensions are tested. A model derived from the factorized form of the dielectric response and including the effect
of Anderson localization in disordered metals, is proposed and found to yield good fit to data with a satisfactory physical
meaning. Data are reduced to a small number of parameters potentially useful for further comparison with other conducting
polymers or even other non-Drude conducting media like oxides.
Received 6 February 2002 / Received in final form 12 August 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: gervais@delphi.phys.univ-tours.fr
RID="b"
ID="b"UMR 6157 CNRS/CEA 相似文献
10.
G. Chaboussant M.-H. Julien Y. Fagot-Revurat M. Hanson L.P. Lévy C. Berthier M. Horvatic O. Piovesana 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):167-181
In a magnetic field, spin-ladders undergo two zero-temperature phase transitions at the critical fields Hc1 and Hc2. An experimental review of static and dynamical properties of spin-ladders close to these critical points is presented. The
scaling functions, universal to all quantum critical points in one-dimension, are extracted from (a) the thermodynamic quantities
(magnetization) and (b) the dynamical functions (NMR relaxation). A simple mapping of strongly coupled spin ladders in a magnetic
field on the exactly solvable XXZ model enables to make detailed fits and gives an overall understanding of a broad class of quantum magnets in their gapless
phase (between Hc1 and Hc2). In this phase, the low temperature divergence of the NMR relaxation demonstrates its Luttinger liquid nature as well as
the novel quantum critical regime at higher temperature. The general behavior close these quantum critical points can be tied
to known models of quantum magnetism.
Received: 13 March 1998 / Received in final form and Accepted: 21 July 1998 相似文献
11.
A. La Magna R. Pucci 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):421-429
In this paper we have introduced a variational approach to investigate the ground state of a model which includes both the
Holstein electron-phonon interaction and the extended Hubbard electron-electron interaction. We have considered a variational
state for the phonon subsystem which generalizes the previous used forms. This state allows to take into account the possibility
of extended phonon mediated correlations. The effective electron Hamiltonian, which we have obtained, includes first and second
neighbor electron-electron interaction terms. We have treated exactly, through a Lanczos method, this effective model in the
one-dimensional case. We have applied our method to two Bechgaard salts and in these cases we have estimated the correlation
parameters. We have shown that the introduction of electron-phonon interaction allows an estimate of the on site U and nearest-neighbor V Coulomb repulsion, which are in agreement with the experimental optical spectra of the above mentioned two compounds.
Received: 30 October 1997 / Revised: 28 January 1998 / Accepted: 10 April 1998 相似文献
12.
R. Clérac M. Fourmigué J. Gaultier Y. Barrans P.A. Albouy C. Coulon 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):445-459
The physical properties of paramagnetic Mo(V) organometallic radical cation salts, , are investigated through the study of two series of solid solutions incorporating two kinds of anions ( or ). The combination of EPR and X-ray diffraction is used to specify the nature of the structural phase transitions which occur
in the paramagnetic phase and to determine the corresponding (
T
,
x
) phase diagrams. Finally, antiferromagnetic resonance is studied to probe the low temperature antiferromagnetic ground state.
In the last part of the paper, the observed complex phase diagram is analyzed by considering a compressible model with at
least two independent modes of compression. We conclude that the larger compressibilities are associated with the smaller
anions.
Received 5 August 1998 相似文献
13.
K.W. Krämer H.U. Güdel P. Fischer F. Fauth M.T. Fernandez-Diaz T. Hauß 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):39-47
ErCl3 crystallizes in the AlCl3-type layer structure. The crystal structure was refined in the paramagnetic state by powder neutron diffraction. The monoclinic
lattice parameters at 1.5 K are a
= 6.8040(3)?, b
= 11.7456(5)?, c
= 6.3187(3)? and . The space group is C2/m. Short-range, predominantly in-plane, magnetic ordering occurs above 350 mK up to several Kelvin.
Below mK a three-dimensional antiferromagnetic order with a propagation vector of sets in. The magnetic structure of ErCl3 was determined by powder and single-crystal neutron diffraction at temperatures down to 45 mK. The Er3+ ions are located on two-dimensional honeycomb layers in the a–b plane. There are two antiferromagnetically coupled triangular sublattices which form right- and left-handed helices along the c-axis. The magnetic moments are oriented in the a–b plane and amount to 3.3(1) at saturation. From the temperature dependence of the integrated neutron magnetic peak intensity a critical exponent (2) was derived for the magnetic phase transition.
Received 1 December 1999 and Received in final form 21 July 2000 相似文献
14.
The spin-1/2 Heisenberg chain: thermodynamics, quantum criticality and spin-Peierls exponents 总被引:1,自引:0,他引:1
A. Klümper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):677-685
We present numerical and analytical results for the thermodynamical properties of the spin-1/2 Heisenberg chain at arbitrary
external magnetic field. Special emphasis is placed on logarithmic corrections in the susceptibility and specific heat at
very low temperatures (T/J=10-24) and small fields. A longstanding controversy about the specific heat is resolved. At zero temperature the spin-Peierls exponent
is calculated in dependence on the external magnetic field. This describes the energy response of the system to commensurate
and incommensurate modulations of the lattice. The exponent for the spin gap in the incommensurate phase is given.
Received: 12 February 1998 / Received in final form: 15 March 1998 / Accepted: 17 March 1998 相似文献
15.
I. Kirschner R. Laiho A.C. Bódi A.D. Caplin E. Lähderanta G. Zsolt 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):389-399
Using a new starting material of Ba2Cu3O5 and a three step heat treatment, single phase Tl2Ca1Ba2Cu2O8 high- superconducting samples have been prepared, possessing the onset- and critical temperatures K and K. The morphology dependent value of is 17 Oe, 8 Oe and 5 Oe at 77 K in the case of bulk, crushed and powdered materials, respectively. The a.c. susceptibility,
r.f. susceptibility and microwave absorption properties show a significant dependence on the particle size with a sharp change
in the interval between 750 μm and 1200 μm. These experiments provide characteristic parameters for intergrain material (treated
as 3D Josephson network) as mm, Oe and A/cm2 at 77 K. The data are controlled by modulated microwave absorption measurements. The results obtained can be explained well
both by the finite size junction model and cavity mode absorption model. The Josephson network is determined unambiguously
by metallic S-N-S weak links.
Received 10 October 1998 相似文献
16.
Drift mobility of charge carriers in p-terphenyl, p-quaterphenyl and tetracene polycrystalline thin films was measured using the classical time-of-flight method. The measurements were carried out both in the atmosphere and in vacuum of the order of 10 - 3 Torr. The mobility measured in the atmosphere is of the order of 10 -4cm2V-1s-1 and turns out to be about 1 order of magnitude higher than that measured in vacuum. It is suggested that the hopping transport of charge dominates in the structures investigated. The increase in the mobility for the measurements in the atmosphere probably results from the additional localized states due to water and other atmosphere molecules. 相似文献
17.
N. Guskos V. Likodimos S. Glenis J. Typek H. Fuks M. Wabia D.G. Paschalidis D. Tossidis C.L. Lin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):277-282
The magnetic properties of the rare earth molecular compounds with hydrazone ligands containing Nd3+, Gd3+, and Yb3+ have been investigated by electron paramagnetic resonance (EPR) and magnetization measurements. For the Gd-compound, partially
resolved fine structure due to Gd3+ and exchange narrowing effects at low temperatures are observed in the EPR spectra, suggesting, consistent with the EPR and
dc magnetic susceptibility, weak antiferromagnetic exchange interactions. Paramagnetic behavior sustained down to low temperatures
is derived for Yb3+ ions, whereas substantial ferromagnetic exchange coupling is inferred for the lighter Nd3+ ions, indicating significant variations of the exchange integrals along the lanthanide series.
Received 29 April 2002 Published online 31 July 2002 相似文献
18.
D. Dantchev J. Rudnick 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):251-268
We study the behavior of systems in which the interaction contains a long-range component that does not dominate the critical
behavior. Such a component is exemplified by the van der Waals force between molecules in a simple liquid-vapor system. In
the context of the mean spherical model with periodic boundary conditions we are able to identify, for temperatures close
above T
c, finite-size contributions due to the subleading term in the interaction that are dominant in this region decaying algebraically as a function of L. This mechanism goes beyond the standard formulation of the finite-size scaling but is to be expected in real physical systems.
We also discuss other ways in which critical point behavior is modified that are of relevance for analysis of Monte Carlo
simulations of such systems.
Received 21 November 2000 and Received in final form 28 February 2001 相似文献
19.
H. Chamati D.M. Dantchev 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):89-99
The finite size behavior of the susceptibility, Binder cumulant and some even moments of the magnetization of a fully finite
O(n) cubic system of size L are analyzed and the corresponding scaling functions are derived within a field-theoretic ɛ-expansion scheme under periodic
boundary conditions. We suppose a van der Waals type long-range interaction falling apart with the distance r as r
- (d + σ), where 2 < σ < 4, which does not change the short-range critical exponents of the system. Despite that the system belongs
to the short-range universality class it is shown that above the bulk critical temperature T
c the finite-size corrections decay in a power-in-L, and not in an exponential-in-L law, which is normally believed to be a characteristic feature for such systems.
Received 8 August 2001 相似文献
20.
EPR study of Dy
3 +
ions in DyBa
2
Cu
3
O
6 + x 总被引:1,自引:0,他引:1
V. Likodimos N. Guskos J. Typek M. Wabia 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):143-147
Concentrated polycrystalline DyBa2Cu3O6+x compounds are studied by X-band EPR spectroscopy. A broad resonance line due to the highly anisotropic EPR spectrum of Dy3+ ions is identified on several specimens at low temperatures. Powder simulation of the EPR spectra complies with the ground
Kramers doublet predicted by crystal field analysis of Dy3+ ions. Calculations of the second and fourth moments of the resonance lines due to the dipole-dipole interactions of Dy3+ indicate the presence of substantial exchange narrowing of the dipolar-broadened EPR linewidth.
Received 3 June 2001 相似文献