共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
S. Haffner M. Dressel D. Groult C. Schlenker 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):167-175
The potassium doped monophosphate tungsten bronzes KxP4W8O32 are two-dimensional metals which show a metal-to-metal transition at a critical temperature which depends on the doping level.
The metal-to-metal transition is accompanied by the formation of a commensurate charge density wave with wave vector (π/b,0) which is independent of the doping level. Undoped P4W8O32, on the other hand, has two metal-to-metal transitions which are connected to the formation of incommensurate charge density
waves. We measured the infrared reflectivity of the series KxP4W8O32 (x
= 0 - 1.57) in the spectral range from 100 to 10 000 cm-1 for room temperature and well below the critical temperature. Polarization-dependent infrared spectra find a two-dimensional
behavior in the normal and the charge density wave state and show signatures of hybridization between one- and two-dimensional
conduction bands. In undoped P4W8O32 the essentials of the charge density wave state can be understood from the nesting vectors of the calculated Fermi surface
and two gaps are observed in the infrared spectra. The gap sizes are a factor of about 2.5 bigger than the predictions from
mean-field theory in the weak-coupling limit which suggests medium- or strong electron-phonon coupling. For potassium doped
KxP4W8O32 one gap is observed in the charge density wave state. The energetics of the charge density formation may be dominated by
the energy required for the lattice modulation.
Received 27 April 2001 and Received in final form 21 September 2001 相似文献
3.
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
4.
F. Maury I. Mirebeau M. Nicolas-Francillon F. Bourée 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):459-466
The magnetic structure of tetragonal insulating YBa2Cu3-xLixOy has been studied as a function of x and y. The Néel temperature and the mean ordered magnetic moment on the Cu2 sites were determined by neutron powder diffraction
measurements. The decrease of these two parameters as compared to YBa2Cu3O6 is much stronger for lithium than for zinc substitution. The difference is quantitatively explained by the presence of holes
created in the CuO2 planes. These holes arise from the substitution of plane Cu2+ by Li+. We suggest an explanation why such holes are not seen for the same substitution of plane Cu2+ by Li+ in orthorhombic superconducting YBa2Cu3-xLixO
7 - δ
.
Received 31 October 2001 and Received in final form 6 March 2002 Published online 25 June 2002 相似文献
5.
M. Gómez Berisso P. Pedrazzini J.G. Sereni O. Trovarelli C. Geibel F. Steglich 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):343-349
We present electrical resistivity and specific heat measurements of alloys on the Rh rich side of the phase diagram of the
Ce(Rh1-xPdx)2Si2 system. We compare these results with those obtained at intermediate and low Rh concentrations. The analysis of the concentration
and temperature dependence of the entropy and of the scaling behaviour of C
el
(
T
) and ρ(
T
) clearly confirm a separation of the magnetic phase diagram into two regions: the region x
≤0.3, showing a concentration independent characteristic temperature for the 4
f-electrons with T
0
≈ 45
K, while for x
> 0.3, T0 decreases to T
0
(
x
= 1) ≈ 15
K. At low Pd-content, TN decreases very rapidly from T
N
= 36
K in pure CeRh2Si2 to T
N
= 18
K at x
= 0.1. With higher Pd concentration TN stabilizes at T
N
≈ 15
K whereas the magnitude of the anomalies in C
el
(
T
) and in the susceptibility around TN are further reduced and disappear at x
≈ 0.3. This differs from the behavior found on the Pd-rich side, where TN decreases continuously to zero with increasing Rh content. The pronounced differences observed between both phase boundaries
and the drastic effect of doping on the Rh rich side suggest an itinerant character in CeRh2 Si2, in contrast with the localized character of CePd2Si2. Further evidence for the itinerant character of CeRh2Si2 is given by the ρ(
T
) dependence observed for x
≤0.3, which scales with ρ(
T
) of the prototype itinerant compound YCo2.
Received 31 December 2001 / Received in final form 6 July 2002 Published online 19 December 2002
RID="a"
ID="a"e-mail: berisso@cab.cnea.gov.ar 相似文献
6.
P. Estrela A. de Visser T. Naka F.R. de Boer L.C.J. Pereira 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):449-454
The effect of hydrostatic pressure ( p
? 1.8 GPa) on the non-Fermi liquid state of U2Pt2In is investigated by electrical resistivity measurements in the temperature interval 0.3-300 K. The experiments were carried
out on single-crystals with the current along (
I
||
c
) and perpendicular (
I
||
a
) to the tetragonal axis. The pressure effect is strongly current-direction dependent. For I
||
a we observe a rapid recovery of the Fermi-liquid T2-term with pressure. A comparison of the data with the magnetotransport theory of Rosch provides evidence for the location
of U2Pt2In at an antiferromagnetic quantum critical point. For I
||
c the resistivity increases under pressure, indicating the enhancement of an additional scattering mechanism.
Received 2 March 2001 and Received in final form 29 June 2001 相似文献
7.
E. Quintero E. Moreno M. Morocoima P. Grima P. Bocaranda M.A. Macías 《Journal of Physics and Chemistry of Solids》2010,71(7):993-735
Magnetic susceptibility χ measurements in the range from 2 to 300 K were carried out on samples of the Cu2FeSnSe4 and Cu2MnSnSe4 compounds. It was found that Cu2FeSnSe4 was antiferromagnetic showing ideal Curie-Weiss behavior with a Néel temperature TN of about 19 K and Curie-Weiss temperature θ=−200 K, while for Cu2MnSnSe4 the behavior was spin-glass with a freezing temperature Tf of about 22 K and Curie-Weiss temperature θ=−25 K. The spin-glass order parameter q(T), determined from the susceptibility data, was found to be in agreement with the prediction of conventional spin-glass theory. 相似文献
8.
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
9.
V.I. Anisimov I.A. Nekrasov D.E. Kondakov T.M. Rice M. Sigrist 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):191-201
The electronic structures of the metallic and insulating phases of the alloy series Ca2-xSrxRuO4 ( 0 ?
x
? 2) are calculated using LDA, LDA+U and Dynamical Mean-Field Approximation methods. In the end members the groundstate respectively
is an orbitally non-degenerate antiferromagnetic insulator (x
= 0) and a good metal (x
= 2). For x
> 0.5 the observed Curie-Weiss paramagnetic metallic state which possesses a local moment with the unexpected spin S
= 1/2, is explained by the coexistence of localized and itinerant Ru-4d-orbitals. For 0.2 <
x
< 0.5 we propose a state with partial orbital and spin ordering. An effective model for the localized orbital and spin degrees
of freedom is discussed. The metal-insulator transition at x
= 0.2 is attributed to a switch in the orbital occupation associated with a structural change of the crystal.
Received 27 July 2001 相似文献
10.
N.A. Babushkina L.M. Belova E.A. Chistotina O.Yu. Gorbenko A.R. Kaul B. Güttler K.I. Kugel 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):409-415
The effect of
16
O
→
18
O isotope substitution on electrical resistivity, magnetoresistance, and ac magnetic susceptibility was studied for La0.35Pr0.35Ca0.3MnO3 epitaxial thin films deposited onto LaAlO3 and SrTiO3 substrates. For the films on LaAlO3, the isotope substitution resulted in the reversible transition from a metal-like to insulating state. The applied magnetic
field ( H
≥ 2
T) transformed the sample with 18O back to the metallic state. The films on SrTiO3 remained metallic at low temperatures for both 16O and 18O, but the shift of the resistivity peak corresponding to onset of metallic state exceeded 63 K after
16
O
→
18
O substitution. The temperature dependence of both resistivity and magnetic susceptibility was characterized by hysteresis,
especially pronounced in the case of the films on LaAlO3. Such a behavior gives certain indications of the phase separation characteristic of interplay between ferromagnetism and
charge ordering.
Received 11 February 2000 and Received in final form 13 September 2000 相似文献
11.
W. Boujelben A. Cheikh-Rouhou J.C. Joubert 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):419-423
Deficiency effects in the A site upon the structural, magnetic and electrical properties in the lacunar perovskite manganite
oxides Pr0.7Sr0.3-x
xMnO3 ( 0 ?
x
? 0.3) and Pr0.7-x
xSr0.3MnO3 ( 0 ?
x
? 0.23) have been investigated. This study focuses on the different parameters which govern the magnetic and electrical properties
in such samples. The powder X-ray diffraction patterns for all samples could be indexed either with a rhombohedral perovskite
structure and R
c space group for x
? 0.2 in strontium deficient samples and for x
? 0.1 for praseodymium deficient ones. For other values of x the samples could be indexed in the orthorhombic structure with Pbnm space group. Magnetic and electrical investigations
show that praseodymium and strontium vacancies do not have similar effects on the lacunar compounds. Magnetization measurements
versus temperature show that all our samples exhibit a magnetic transition when the temperature decreases. All the praseodymium
deficient samples exhibit a paramagnetic-ferromagnetic transition when the temperature decreases while the strontium deficient
ones exhibit this transition only for low x values. The magnetic transition temperature shifts to lower values as the strontium deficiency increases (from 265 K for
x
= 0 to 90 K for x
= 0.3) and to higher values with the praseodymium deficiency increase (from 265 K for x
= 0 to 315 for x
= 0.23). Resistivity measurements as a function of temperature show a semiconducting-metallic transition for all x values in the praseodymium lacunar samples and only for low x values ( 0 ?
x
? 0.1) in the strontium lacunar ones when the temperature decreases.
Received 12 April 2000 and Received in final form 8 January 2001 相似文献
12.
P. Roussel P. Foury-Leylekian B. Domengès D. Groult P. Labbé J.-P. Pouget 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):497-508
A new variety of P
4
W
10
O
38
, m
= 5 member of the monophosphate tungsten-bronze family with pentagonal tunnels (MPTB
p), , has been isolated and studied by X-ray diffraction measurements. The structure has been solved by direct methods from single
crystal X-ray data. The monoclinic unit cell corresponds to a regular stacking of WO
3
-type slabs which are all five-WO
6
-octahedra thick and connected through PO
4
tetrahedra. This structure is comparable to that previously described for the MPTB
p'series with m
= 4 (P
4
W
8
O
32
) and m
= 6 (P
4
W
12
O
44
). An X-ray diffuse scattering investigation has revealed that this member is subjected to charge density wave instabilities
(CDW) located on chains running along the directions. Two CDW transitions have been observed at and , bearing some resemblance with those exhibited by the m
= 4 member. The corresponding modulation wave vectors can be accounted for by a hidden nesting mechanism which connects the crossing
points of differently oriented quasi-planar Fermi surfaces, as found for the low m (4 and 6) members of the MPTB's.
Received 12 March 1999 and received in final form 20 May 1999 相似文献
13.
A.M. Balagurov V.Yu. Pomjakushin D.V. Sheptyakov V.L. Aksenov N.A. Babushkina L.M. Belova O.Yu. Gorbenko A.R. Kaul 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):215-223
The atomic structure of (
La
1 - y
Pr
y
)
0.7
Ca
0.3
MnO
3
compound with 0.5≤
y
≤1 has been systematically studied by neutron powder diffraction in the temperature range from 15 to 293 K. For composition
with y
= 0.75, the structural analysis was performed on two samples, one containing the natural mixture of oxygen isotopes and the other
one 75% enriched by
18
O. The room temperature structural characteristics of the series, including cell volume, average Mn-O bond distance, and average
Mn-O-Mn bond angle, are the linear functions of the <
r
A
>. Temperature dependencies of these parameters are quite smooth, except for the point T
=
T
FM
, where a jump like changes occur. The isotope enriched samples have been found identical in crystal and magnetic structure
down to the temperature of transition of the sample with
16
O into the metallic ferromagnetic phase. It confirms that different transport and magnetic properties of the samples with
16
O and
18
O at low temperature are driven by the different oxygen atoms dynamics solely. Temperature dependencies of the CO and AFM diffraction
peak intensities and of the peak widths for compositions close to the metal-insulator boundary ( y
≈ 0.75) indicate the macroscopically phase separated AFM-dielectric + FM-metallic state below T
FM
.
Received 28 April 2000 相似文献
14.
F. Reynaud A.M. Ghorayeb Y. Ksari N. Menguy A. Stepanov C. Delmas 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):83-90
In this work, results of X-band ESR spectroscopy, ac-magnetic susceptibility and X-ray powder diffraction measurements on
Li1-xNi
1+x
O2 (x
= 0.02 and x
= 0.07) are presented and discussed. While the susceptibility of the compound with x
= 0.02 is shown to follow a Curie-Weiss law, with a Weiss temperature of the order of 30 K, the compound with x
= 0.07 is found to order ferromagnetically below K. However, an additional anomaly is observed in the magnetic properties of this latter compound at around 240 K. We attribute this anomaly to the presence of macroscopic Ni-rich regions which order ferrimagnetically below this temperature.
This phenomenon is different from the bulk ferromagnetism that occurs at much lower temperatures, and allows us to discard
earlier suggestions proposed in the literature in which the 240 K anomaly has been considered as denoting an intrinsic phenomenon.
Received 14 May 1999 and Received in final form 5 August 1999 相似文献
15.
Y. Piskunov D. Jérome P. Auban-Senzier P. Wzietek C. Bourbonnais U. Ammerhal G. Dhalenne A. Revcolevschi 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):443-456
63Cu-NMR measurements have been performed on two-leg hole-doped spin ladders Sr14-xCaxCu24O41 single crystals 0 ?
x
? 12 at several pressures up to the pressure domain where the stabilization of a superconducting ground state can be achieved.
The data reveal a marked decrease of the spin gap derived from Knight shift measurements upon Ca substitution and also under
pressure and confirm the onset of low lying spin excitations around P
c
as previously reported. The spin gap in Sr
2
Ca
12
Cu
24
O
41
is strongly reduced above 20 kbar. However, the data of an experiment performed at P
= 36 kbar where superconductivity has been detected at 6.7 K by an inductive technique have shown that a significant amount of
spin excitations remains gapped at 80 K when superconductivity sets in. The standard relaxation model with two and three-magnon
modes explains fairly well the activated relaxation data in the intermediate temperature regime corresponding to gapped spin
excitations using the spin gap data derived from Knight shift experiments. The data of Gaussian relaxation rates of heavily
doped samples support the limitation of the coherence length at low temperature by the average distance between doped holes.
We discuss the interplay between superconductivity and the spin gap and suggest that these new results support the exciting
prospect of superconductivity induced by the interladder tunneling of preformed pairs as long as the pressure remains lower
than the pressure corresponding to the maximum of the superconducting critical temperature.
Received 8 March 2001 and Received in final form 27 July 2001 相似文献
16.
A. Vecchione M. Gombos S. Pace L. Marchese G. Cerrato C. Tedesco P.W. Stephens C. Noce 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):51-55
We report the preparation and the structural and morphological characterization of the perovskite compound NdSr2RuCu2Oy. The crystal structure of this material has been determined by a combined high-resolution electron microscopy, selected area
electron diffraction and high-resolution X-ray powder diffraction study. The morphology of the samples has been monitored
by a scanning electron microscope equipped with an energy dispersive spectrometer attachment by which the microanalysis of
the crystallites has been also performed. Finally, dc magnetic susceptibility measurements show that this compound behaves
like an enhanced paramagnetic metal with evidence of neither magnetic order and neither superconducting one.
Received 15 November 2001 相似文献
17.
P. Zieliński W. Schranz D. Havlik A.V. Kityk 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):155-165
A four-state pseudospin model is constructed for the isomorphous phase transition hcp-2↦hcp-1 in pure C70 and in C70-rich mixed crystal C
70(1 - x)
C60x. With the specific anisotropic pseudospin interactions adapted to the C70 crystal the model is equivalent to a two-state Ising model in a temperature-dependent field. Replica symmetric state of the
model is shown to approach the critical point when the width of distribution of random fields and/or of random bonds increases.
The temperature of the phase transition and the phase equilibrium temperature then are practically constant, whereas the experiment
shows their strong decrease with x. The main effect of dilution resides in an x-dependence of the model parameters. Dilatometric data on the hexagonal C
70(1 - x)
C60x are used to fit these parameters. A metastable disordered phase subsisting below the phase transition is discovered in a
range of the model parameters and is shown to be responsible for the macroscopic behaviour of the system. A good agreement
with experimental data is obtained for the spontaneous strain and for the x-dependence of the hysteresis.
Received 20 April 2001 and Received in final form 26 September 2001 相似文献
18.
N. Bouarissa 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):139-143
Pseudopotential investigation of energy band gaps and charge distribution in quasi-binary (GaSb)1-x(InAs)x crystals has been reported. To the best of our knowledge, there had been no reported theoretical work on these materials.
In agreement with experiment, the quasi-binary crystals of interest showed a significant narrowing of the optical band gap
compared to the conventional GaxIn1-xAsySb1-y quaternary alloys (with x
= 1 -
y). Moreover, the absorption at the optical gaps indicated that (GaSb)1-x(InAs)x is a direct Γ to Γ band-gap semiconductor within a whole range of the x composition. The information derived from the present study predicts that the band gaps cross very important technological
spectral regions and could be useful for thermophotovoltaic applications.
Received 30 August 2002 Published online 1st April 2003
RID="a"
ID="a"Present address: Physics Department, University of M'sila, 28000 M'sila, Algeria e-mail: N_Bouarissa@yahoo.fr 相似文献
19.
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
20.
F.S. da Rocha G.L.F. Fraga D.E. Brand?o C.M. Granada C.M. da Silva A.A. Gomes 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):307-311
The magnetic moment of the Mn impurities was obtained from magnetization measurements of Y
(
Ni
1 - x
Mn
x
)
2
B
2
C as a function of the concentration x less than 0.15. Using the coherent potential approximation and starting from 3
d density of states, obtained from the first principles calculations, the magnetic moments are obtained within a two sublattice
model. For adequately estimated values of the Coulomb interactions U, the position of the energy level of Mn and adopting values for the intersublattice hybridization term, a qualitative agreement
with the observed experimental data is obtained.
Received 23 April 2001 and Received in final form 29 October 2001 相似文献