共查询到20条相似文献,搜索用时 15 毫秒
1.
B. Schmidt V. Yushankhai L. Siurakshina P. Thalmeier 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):43-47
A pronounced Curie-like upturn of the magnetic susceptibility χ(
T
) of the quasi one-dimensional spin chain compound Ba2V3O9 has been found recently [#!kaul:02!#]. Frequently this is taken as a signature for a staggered field mechanism due to the
presence of g-factor anisotropy and Dzyaloshinskii-Moriya interaction. We calculate this contribution within a realistic structure of vanadium
3
d- and oxygen 2
p-orbitals and conclude that this mechanism is far too small to explain experimental results. We propose that the Curie term
is rather due to a segmentation of spin chains caused by broken magnetic bonds which leads to uncompensated S
= ? spins of segments with odd numbers of spins. Using the finite-temperature Lanczos method we calculate their effective moment
and show that ∼ 1% of broken magnetic bonds is sufficient to reproduce the anomalous low-T behavior of χ(
T
) in Ba2V3O9.
Received 19 December 2002 / Received in final form 29 January 2003 Published online 14 March 2003 相似文献
2.
We show that non-frustrated and frustrated ladders in a magnetic field can be systematically mapped onto an XXZ Heisenberg model in a longitudinal magnetic field in the limit where the rung coupling is the dominant one. This mapping
is valid in the critical region where the magnetization goes from zero to saturation. It allows one to relate the properties
of the critical phase (H
c
1, H
c
2, the critical exponents) to the exchange integrals and provide quantitative estimates of the frustration needed to create
a plateau at half the saturation value for different models of frustration.
Received: 7 May 1998 / Revised and Accepted: 10 July 1998 相似文献
3.
4.
B. Canals D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):439-447
Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the checkerboard lattice are
studied for the exactly solvable infinite-component spin-vector model, D↦∞. In contrast to conventional two-dimensional magnets with continuous symmetry showing extended short-range order at distances
smaller than the correlation length, r
ξ
c∝ exp(T
*/T), correlations in the checkerboard-lattice model decay already at the scale of the lattice spacing due to the strong degeneracy
of the ground state characterized by a macroscopic number of strongly fluctuating local degrees of freedom. At low temperatures,
spin CFs decay as <
>∝ 1/r
2 in the range a
0≪r≪ξ
c∝T
-1/2, where a0 is the lattice spacing. Analytical results for the principal thermodynamic quantities in our model are very similar with
MC simulations, exact and analytical results for the classical Heisenberg model (D = 3) on the pyrochlore lattice. This shows that the ground state of the infinite-component spin vector model on the checkerboard
lattice is a classical spin liquid.
Received 16 November 2001 and Received in final form 12 February 2002 相似文献
5.
Unconventional antiferromagnetic correlations of the doped Haldane gapsystem Y 2 BaNi 1 - x Zn x O 5
V. Villar R. Mélin C. Paulsen J. Souletie E. Janod C. Payen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):39-51
We make a new proposal to describe the very low temperature susceptibility of the doped Haldane gap compound Y2BaNi1-xZnxO5. We propose a new mean field model relevant for this compound. The ground state of this mean field model is unconventional
because antiferromagnetism coexists with random dimers. We present new susceptibility experiments at very low temperature.
We obtain a Curie-Weiss susceptibility χ(
T
) ∼
C
/(Θ +
T
) as expected for antiferromagnetic correlations but we do not obtain a direct signature of antiferromagnetic long range order.
We explain how to obtain the “impurity” susceptibility
(
T
) by subtracting the Haldane gap contribution to the total susceptibility. In the temperature range [1 K, 300 K] the experimental
data are well fitted by T
(
T
) =
C
imp
1 +
T
imp
/
T
. In the temperature range [100 mK, 1 K] the experimental data are well fitted by T
(
T
) =
A
ln(
T
/
T
c
), where T
c
increases with x. This fit suggests the existence of a finite Néel temperature which is however too small to be probed directly in our experiments.
We also obtain a maximum in the temperature dependence of the ac-susceptibility
(
T
) which suggests the existence of antiferromagnetic correlations at very low temperature.
Received 17 July 2001 相似文献
6.
H. Schwenk S. Bareiter C. Hinkel B. Lüthi Z. Kakol A. Koslowski J.M. Honig 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):491-494
We present the temperature dependence of elastic modes of Fe3-xZnxO4 with x
= 0, x
= 0.02 and x
= 0.032. The c44 shear modes show a pronounced softening which can be normalized to a common behavior for all these substances. We can explain
the softening with a bilinear coupling of the elastic strain to an order parameter linked to charge ordering processes. The
other elastic modes (c11, c12 and the bulk modulus) do not show any softening. We present a symmetry analysis for the charge ordering model.
Received 27 April 1999 相似文献
7.
J. Schnack H.-J. Schmidt J. Richter J. Schulenburg 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):475-481
For many spin systems with constant isotropic antiferromagnetic next-neighbour Heisenberg coupling the minimal energies E
min(S) form a rotational band, i.e. depend approximately quadratically on the total spin quantum number S, a property which is also known as Landé interval rule. However, we find that for certain coupling topologies, including
recently synthesised icosidodecahedral structures this rule is violated for high total spins. Instead the minimal energies
are a linear function of total spin. This anomaly results in a corresponding jump of the magnetisation curve which otherwise
would be a regular staircase.
Received 27 August 2001 and Received in final form 18 October 2001 相似文献
8.
V.A. Pashchenko A. Sulpice F. Mila P. Millet A. Stepanov P. Wyder 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):473-476
We report on the magnetic susceptibility and electron spin resonance measurements on polycrystalline samples of the vanadium
oxide VOSb2O4, a quasi-one-dimensional S
= 1/2 Heisenberg system. The susceptibility vanishes at zero temperature, but there is no cusp at the onset of the susceptibility
drop, and the ESR linewidth exhibits an increase characteristic of a phase transition at a much lower temperature. We show
that this behaviour is consistent with the formation of a pseudo-gap in a spin-Peierls system in the adiabatic limit.
Received 7 February 2001 and Received in final form 24 April 2001 相似文献
9.
M. Mambrini F. Mila 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):651-659
Extensive calculations in the short-range RVB (Resonating valence bond) subspace on both the trimerized and the regular (non-trimerized)
Heisenberg model on the kagomé lattice show that short-range dimer singlets capture the specific low-energy features of both models. In the trimerized case
the singlet spectrum splits into bands in which the average number of dimers lying on one type of bonds is fixed. These results
are in good agreement with the mean field solution of an effective model recently introduced. For the regular model one gets
a continuous, gapless spectrum, in qualitative agreement with exact diagonalization results.
Received 7 March 2000 相似文献
10.
P. Horsch F. Mack 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):367-370
The present understanding of the electronic and magnetic properties of -NaV2O5 is based on the hypothesis of strong charge disproportionation into V4+ and V5+, which is assumed to lead to a spin-1/2 Heisenberg chain system. A recent structure analysis shows, however, that the V-ions
are in a mixed valence state and indistiguishable. We propose an explanation for the insulating state, which is not based
on charge modulation, and show that strong correlations together with the Heitler-London character of the relevant intermediate
states naturally lead to antiferromagnetic Heisenberg chains. The interchain coupling is weak and frustrated, and its effect
on the uniform susceptibility is found to be small.
Received: 28 January 1998 / Accepted: 17 March 1998 相似文献
11.
F. Pérez-Willard A. Faißt J. Wosnitza H.. v. Löhneysen U. Schotte H. Tanaka 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):247-251
We report on the magnetic phase diagram of the distorted triangular-lattice antiferromagnet RbCuCl3 for a magnetic field applied parallel to the basal plane (). High-resolution measurements of the specific heat and of the magnetocaloric effect have been performed in magnetic fields
up to 14 T. The high-field specific-heat data reveal the existence of an intermediate phase between the paramagnetic and the
frustrated antiferromagnetic phase.
Received 18 October 1999 相似文献
12.
M.E. Gouvêa A.S.T. Pires 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):147-153
We use the self-consistent harmonic approximation (SCHA) to study the two-dimensional classical Heisenberg anisotropic (easy-plane)
ferromagnetic model including nearest- and next-nearest neighbor exchange interactions. For temperatures much lower than the
Kosterlitz-Thouless phase transition temperature T
KT, spin waves must be the most relevant excitations in the system and the SCHA must account for its behavior. However, for
temperatures near T
KT, we should expect vortex pairs to be quite important. The effect of these vortex excitations on the phase transition temperature
is included in our theory as a renormalization of the exchange interactions. Then, combining the SCHA theory to the renormalization
effect due to vortex pairs, we calculate the dependence of T
KT as a function of the easy-plane anisotropies and exchange interactions.
Received 3 April 2001 and Received in final form 20 September 2001 相似文献
13.
J.V. Alvarez Claudius Gros 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):641-648
We present an efficient way to compute diagonal and off-diagonal n-point correlation functions for quantum spin-systems within the loop algorithm. We show that the general rules for the evaluation
of these correlation functions take an especially simple form within the framework of directed loops. These rules state that
contributing loops have to close coherently. As an application we evaluate the specific heat for the case of spin chains and
ladders.
Recieved 10 January 2000 and Received in final form 9 February 2000 相似文献
14.
D. Hupfeld W. Schweika J. Strempfer W.A. Caliebe U. Köbler K. Mattenberger G.J. McIntyre F. Yakhou Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):273-289
We report on an investigation of the magnetic properties of Gd
x
Eu
1 - x
S mixed crystals with compositions in the range of 0.6 <
x
< 1. For the two samples Gd
0.8
Eu
0.2
S and Gd
0.73
Eu
0.27
S a long-range antiferromagnetic order was observed at low temperatures. Element-specific measurements exhibited a different
temperature dependence of the reduced sublattice magnetisation of the two magnetic species. A model calculation and Monte
Carlo simulations revealed that the different temperature dependence is due to frustration effects. These frustration effects
lead to a breakdown of the long-range order for higher europium contents. For the Gd
0.67
Eu
0.33
S-sample we were able to observe a short-range antiferromagnetic order with correlation lengths of a few 10? with X-ray resonance exchange scattering.
Received 25 April 2001 and Received in final form 3 December 2001 相似文献
15.
M. Affronte J.C. Lasjaunias A. Cornia 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):633-639
The effects of the internal guest substitution within hexa-iron molecular rings (Na:Fe6 and Li:Fe6) have been investigated
by means of low temperature specific heat (LTSH) measurements. By changing Na to Li as central metal ion, the Schottky anomaly
shifts towards lower temperatures. The data analysis is supported by the study of the LTSH of the non-magnetic Na:Ga6 compound
which has the same core structure as the iron rings. For the non-magnetic Na:Ga6, significant deviations from the simple Debye law were found and the use of conventional C
vs.
T fitting curves is critically discussed. The singlet-triplet energy gap ( K) and its zero-field splitting ( K) evaluated from the magnetic contribution of the Li:Fe6 LTSH are compared to values estimated by high field torque magnetometry.
Received 25 November 1999 相似文献
16.
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
17.
N. Shannon 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):527-540
Above 40 K, the magnetic susceptibility of the heavy Fermion spinel LiV2O4 has many features in common with those of geometrically frustrated magnetic insulators, while its room temperature resistivity
comfortably exceeds the Mott-Regel limit. This suggests that local magnetic moments, and the underlying geometry of the pyrochlore
lattice, play an important role in determining its magnetic properties. We extend a recently introduced tetragonal mean field
theory for insulating pyrochlore antiferromagnets to the case where individual tetrahedra contain spins of different lengths,
and use this as a starting point to discuss three different scenarios for magnetic and electronic transitions in LiV2O4.
Received 12 March 2002 and Received in final form 3 May 2002 Published online 25 June 2002 相似文献
18.
L.F. Lemmens F. Brosens J.T. Devreese 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):195-202
A full analysis of domain structure using a micromagnetic model is developed in order to get a clear insight into the behaviour
of transverse initial susceptibility as a function of dc applied field for thin films and bilayers exhibiting both in-plane
and perpendicular anisotropy. The numerical simulations are in good agreement with available experimental results in case
of single layers with the so-called stripe domain pattern while some predictions are done for bilayers. As the main result,
it is shown that in low field, the transverse initial susceptible cannot be interpreted without the knowledge of the static
domain pattern while, above saturation, it is only affected by the in-plane anisotropy.
Received 10 October 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: ml@lpmtm.univ-paris13.fr
RID="b"
ID="b"UMR CNRS 8634 相似文献
19.
A general theory of critical sound propagation, including phonon-spin-energy coupling, is studied in anisotropic magnets above
their transition temperature. The Kawasaki weak singularity in the ultrasonic attenuation is found as a nonasymptotic effect.
A new nonasymptotic regime similar to the one in the binary mixture is also determined. The role of coupling constants and
the bare relaxation times in establishing the dominance region of particular terms, is discussed.
Received: 9 December 1997 / Accepted: 24 February 1998 相似文献
20.
J.R.L. de Almeida 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):289-295
A high dimensionality calculation (Weiss like) has been carried out for antiferromagnetism (AFM) in structures with many sublattices.
By allowing quenched disorder in the exchange interactions our results clearly exhibit the interplay between the effects of
lattice frustration and disorder on the system's properties. For given number of sublattices present, there are several possible
phases (ordering of the spins) and as many metastable states in the ergodic phases. It is found that the glassy behavior,
and metastability, for multi-sublattices systems is substantially enhanced as compared with simple structures, exhibiting
structure dependent de Almeida-Thouless lines. Strongly disordered systems have the long-range AFM ordering, ergodic metastable
states and glassy phases intermingled in a non-trivial way. Also, even small fluctuations in the exchange parameters do induce
sizeable glassy behavior in structures with many sublattices. Spin glass behavior in apparently non-disordered systems as
certain pyrochlores may be accounted for within the present context.
Received 9 April 1999 and Received in final form 8 June 1999 相似文献