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1.
D. Barba S. Jandl A.A. Martin C.T. Lin M. Cardona T. Wolf 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):277-281
Infrared reflectance, and transmission measurements as well as Raman scattering have been used to study the RE1+xBa2-xCu3O6 (RE = Nd, Sm) and YBa2Cu3O6 absorption bands in the 1100-1500 cm-1 infrared range as a function of temperature and beam polarization. In addition to two-phonon absorption between 1100 and
1170 cm-1, we observe excitations around 1400 cm-1, occurring in oxygen rich enclosures within the samples, and assign them to an excitation involving two-phonons plus the
270 cm-1 local mode related to Cu-O broken chains. Thus, the previously reported possible magnetic origin of the 1436 cm-1 sharp absorption band in YBa2Cu3O6 is contested.
Received 14 February 2001 and Received in final form 12 April 2001 相似文献
2.
M. Gaudry J. Lermé E. Cottancin M. Pellarin B. Prével M. Treilleux P. Mélinon J.-L. Rousset M. Broyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):201-204
Optical properties of mixed clusters (AuxAg
1 - x
)
n
and (NixAg
1 - x
)
n
, produced by laser vaporization and embedded in an alumina matrix, are reported. The size effects are investigated for different
concentrations (x
= 0.25, 0.5 and 0.75) in the diameter range 2-4 nm. For alloyed clusters (AuxAg
1 - x
)
n
of a given size an almost linear evolution of the surface plasmon frequency ω
s
with the concentration is observed (between those of pure gold and pure silver clusters). Moreover the blue-shift and the
damping of the resonance with decreasing size is all the more important as the gold concentration in the particles increases.
Such results are in agreement with theoretical calculations carried out in the frame of the time-dependent local-density-approximation
(TDLDA) including an inner skin of ineffective screening and the porosity of the matrix. The optical response of (NixAg
1 - x
)
n
clusters exhibits a surface plasmon resonance in the same spectral range as the one observed for pure silver clusters, but
considerably damped and broadened. For a given mean cluster size 3.0 nm, a blue-shift of the resonance is observed when increasing
the nickel concentration (between x
= 0.25 and x
= 0.75). The results are in good qualitative agreement with classical predictions in the dipolar approximation, assuming a core-shell
geometry.
Received 21 November 2000 相似文献
3.
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
4.
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
5.
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
6.
C.J. Calzado J.-P. Malrieu 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):375-381
Accurate ab initio calculations on embedded Cu4O12 square clusters, fragments of the La2CuO4 lattice, confirm a value of the nearest neighbor antiferromagnetic coupling (J
= 124 meV) previously obtained from ab initio calculations on bicentric clusters and in good agreement with experiment. These calculations predict non negligible antiferromagnetic
second-neighbor interaction (J'
= 6.5 meV) and four-spin cyclic exchange (K
= 14 meV), which may affect the thermodynamic and spectroscopic properties of these materials. The dependence of the magnetic
coupling on local lattice distortions has also been investigated. Among them the best candidate to induce a spin-phonon effect
seems to be the movement of the Cu atoms, changing the Cu-Cu distance, for which the variation of the nearest neighbor magnetic
coupling with the Cu-O distance is Δ
J
/Δ
d
Cu - O
∼ 1700 cm-1?-1.
Received 20 November 2000 相似文献
7.
N. Petit V. Garnier V. Ta Phuoc R. Caillard A.-M. Frelin A. Ruyter I. Laffez J.-C. Soret A. Maignan F. Gervais 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):423-429
The reflectivity spectra of an oriented ceramic of Bi-2223 has been investigated by polarized infrared reflectivity spectroscopy
in the energy range 0.005-2.2 eV. It is shown that the data for the polarization parallel to the c axis cannot be fitted with a one-component Drude or extended-Drude model. The conductivity spectrum is then obtained from
the best fit of a “double-damping Drude” model to reflectivity spectra, itself derived from the factorized form of the dielectric
function, and by a Kramers-Kronig inversion as well. The data and their analysis give a new insight of the 2D character of
the system.
Received 26 April 2001 and Received in final form 28 August 2001 相似文献
8.
R. Beuc H. Skenderovi T. Ban D. Vea G. Pichler W. Meyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):209-214
We measured a very distinct satellite band at 875.2 nm between two resonance lines of cesium. Spectral simulation using Spies
and Meyer [#!ref1!#] ab initio potential curves and an appropriate transition dipole moment function was compared with experimental profile. Implications
of the investigated satellite band at 875.2 nm in the field of ultracold cesium atom collisions are discussed with a special
emphasize to new possibilities of the photoassociation of two ground state atoms leading to the formation of ultracold intermediate
long-range molecules.
Received 07 March 2001 and Received in final form 14 May 2001 相似文献
9.
D. Vignolles A. Audouard L. Brossard S. Pesotskii R. Lyubovskii M. Nardone E. Haanappel R. Lyubovskaya 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):53-61
Interlayer magnetoresistance and magnetisation of the quasi-two dimensional organic metal (BEDT-TTF)8Hg4Cl12(C6H5Br)2 have been investigated in pulsed magnetic fields extending up to 60 T and 33 T, respectively. About fifteen fundamental frequencies,
composed of linear combinations of only three basic frequencies, are observed in the oscillatory spectra of the magnetoresistance.
The dependencies of the oscillation amplitude on the temperature and on the magnitude and orientation of the magnetic field
are analyzed in the framework of the conventional two-dimensional Lifshitz-Kosevitch (LK) model. This model is implemented
by damping factors which accounts for the magnetic breakthrough occurring between electron and hole orbits yielding conventional
Shubnikov-de Haas closed orbits (model of Falicov and Stachowiak) and quantum interferometers. In particular, a quantum interferometer
enclosing an area equal to the first Brillouin zone area is evidenced. The LK model consistently accounts for the temperature
and magnetic field dependence of the oscillation amplitude of this interferometer. On the contrary, although this model formally
accounts for almost all of the observed oscillatory components, it fails to give consistent quantitative data in most other
cases.
Received 4 September 2002 / Received in final form 14 November 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: audouard@insa-tlse.fr
RID="b"
ID="b"UMR 5830: Unité Mixte de Recherche CNRS - Université Paul Sabatier - INSA de Toulouse
RID="c"
ID="c"UMS 5642: Unité Mixte de Service CNRS - Université Paul Sabatier - INSA de Toulouse 相似文献
10.
We present the magnetic and thermal properties of a series of compounds RE2Al3Si2 for RE=Dy, Ho, Er, and REAlSi for RE=Pr, Ce. The 2–3–2 family crystallizes with themonoclinic Y2Al3Si2-type structure while the 1–1–1 family crystallizes in the body-centered tetragonal α-ThSi2-type structure. The measurements were done on single crystals, grown using high-temperature flux technique and molten Al as a solvent . Susceptibility and heat capacity data were taken from 1.8 to 200 K, from the heat capacity data, the isothermal magnetic entropy change was obtained. Our results indicate signal oscillations in magnetocaloric properties for those compounds, in particular, Dy2Al3Si2 that shows an anomaly that can be associated with a spin reorientation. Similar results are known for some Dy discilicides and dialluminades. 相似文献
11.
A. Maignan C. Martin M. Hervieu B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):41-45
The substitution of manganese for cobalt in the perovskite La
0.8
Sr
0.2
CoO
3
has been studied. A significant increase of the magnetoresistance (MR) is obtained, reaching 60% at 5 K under 7 T for . This behavior originates from a spectacular increase of the resistivity correlated to a significant decrease of ferromagnetism
by Mn doping. This enhancement of magnetoresistance can be interpreted by the growth of ferromagnetic clusters in the insulating
matrix, by applying a magnetic field.
Received 7 May 1999 相似文献
12.
T. Nzeyimana E.A. Naji X. Urbain A. Le Padellec 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):315-325
Total cross-sections have been measured for the associative ionisation of C
+
+
O
-
, N
+
+
O
-
and O
+
+
O
-
by means of a merged-beam set-up operating with keV beams. These original measurements might be relevant to the understanding
of some astrophysical objects or laboratory-made plasmas (flames and etching plasmas). The magnitude of these cross-sections
is particularly large whatever the associating system, as these are in the range of 1×10
-14
cm2 at thermal energies. Their behaviour as a function of energy significantly differs from one system to another, and is characterised
by the Wigner law at low energy, and a rapid fall-off at higher energy due to competition with non-associative ionisation
processes.
Received 10 December 2001 and Received in final form 12 March 2002 相似文献
13.
A. Sherman M. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):203-214
Using the method which retains the rotation symmetry of spin components in the paramagnetic state and has no preset magnetic
ordering, spectral and magnetic properties of the two-dimensional t-J model in the normal state are investigated for the ranges of hole concentrations 0 ⩽ x ⩽ 0.16 and temperatures 0.01t ⩽ T ⩽ 0.2t. The used hopping t and exchange J parameters of the model correspond to hole-doped cuprates. The obtained solutions are homogeneous which indicates that stripes
and other types of phase separation are not connected with the strong electron correlations described by the model. A series
of nearly equidistant maxima in the hole spectral function calculated for low T and x is connected with hole vibrations in the region of the perturbed short-range antiferromagnetic order. The hole spectrum has
a pseudogap in the vicinity of (0,π) and (π, 0). For x ≈ 0.05 the shape of the hole Fermi surface is transformed from four small ellipses around (±π/2,±π/2) to two large rhombuses
centered at (0, 0) and (π,π). The calculated temperature and concentration dependencies of the spin correlation length and
the magnetic susceptibility are close to those observed in cuprate perovskites. These results offer explanations for the observed
scaling of the static uniform susceptibility and for the changes in the spin-lattice relaxation and spin-echo decay rates
in terms of the temperature and doping variations in the spin excitation spectrum of the model.
Received 14 November 2002 Published online 1st April 2003
RID="a"
ID="a"e-mail: alexei@fi.tartu.ee 相似文献
14.
E. Arrigoni G.C. Strinati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):433-448
We study the zero-temperature spin fluctuations of a two-dimensional itinerant-electron system with an incommensurate magnetic
ground state described by a single-band Hubbard Hamiltonian. We introduce the (broken-symmetry) magnetic phase at the mean-field
(Hartree-Fock) level through a spiral spin configuration with characteristic wave vector Q different in general from the antiferromagnetic wave vector Q
AF, and consider spin fluctuations over and above it within the electronic random-phase (RPA) approximation. We obtain a closed system of equations for the generalized wave vector and frequency dependent susceptibilities, which are equivalent to the
ones reported recently by Brenig. We obtain, in addition, analytic results for the spin-wave dispersion relation in the strong-coupling
limit of the Hubbard Hamiltonian and find that at finite doping the spin-wave dispersion relation has a hybrid form between that associated with the (localized) Heisenberg model and that associated with the (long-range) RKKY exchange interaction.
We also find an instability of the spin-wave spectrum in a finite region about the center of the Brillouin zone, which signals
a physical instability toward a different spin- or, possibly, charge-ordered phase, as, for example, the stripe structures
observed in the high-T
c materials. We expect, however, on physical grounds that for wave vectors external to this region the spin-wave spectrum that
we have determined should survive consideration of more sophisticated mean-field solutions.
Received 15 September 2000 相似文献
15.
V. Ghanbarian M. R. Mohammadizadeh 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(3):309-318
Electric-field gradient (EFG) and asymmetry parameter (η) at all
oxygen and copper sites of nonsuperconducting PrBa2Cu3O7
(Pr123) compound were calculated using the full-potential
(linearized)-augmented-plane-wave plus local orbitals method. Exchange and
correlation effects were treated by LSDA+U for Cu(3d) and Pr(4f) electrons.
The effects of changing screened Coulomb parameters UPr, UCu1, and
UCu2 on the results were individually studied. The calculated EFG of O2
site is close to the EFG of O3 site at variance with the experimental
result. It was shown that by increasing superconducting holes in O2 and O3
sites the EFG at these sites increase and vice versa. The most famous
theories which have been proposed to explain the suppression of
superconductivity in perfect (without any mis-substitution or other defects)
Pr123 compound are not consistent with the experimental EFG at O2 and O3
sites. By replacing one Pr atom at the Ba site on unit cell of Pr123
(PrBa), it was shown that PrBa mis-substitution reduces the
superconducting holes in both O2 and O3 sites and could be responsible for
the suppuration of superconductivity in Pr123 samples. It is very probable
that the unusual behaviors of experimental EFG at O2 and O3 sites of Pr123
are related to oxygen defects which are produced with PrBa
mis-substitution. 相似文献
16.
E. Muñoz-Sandoval J. Dorantes-Dávila G.M. Pastor 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(1):89-96
The electronic and magnetic properties of clusters are investigated in the framework of the Hubbard model by treating electron
correlations effects in a saddle-point slave-boson approximation. The size dependent single-particle spectrum is calculated
using a third moment real-space expansion of the local density of states. Results for the magnetic moments, magnetic order,
average number of double occupations and hopping renormalizations are given as a function of the local coordination number
z, for different representative values of the Coulomb interaction strength U/t and band filling n. Several transitions between paramagnetic, ferromagnetic and antiferromagnetic behaviors are obtained as a function of z. The environment dependence of the magnetic behavior and of the degree of electron delocalization is analyzed. Advantages
and limitations of the present approach are discussed.
Received: 8 January 1998 / Revised: 22 June 1998 / Accepted: 6 August 1998 相似文献
17.
P. Lehnen W. Kleemann Th. Woike R. Pankrath 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):633-637
The linear birefringence (LB) of Sr
0.61-x
Ba
0.39
Nb
2
O
6
:Ce
3+
x (SBN61:Ce) has been measured as a function of temperature within the range of . Large tails have been observed above the ferroelectric phase transition temperatures T
c
= 350, 328, 320 and 291 K for the concentrations x
= 0, 0.0066, 0.0113 and 0.0207, respectively. Within an Ornstein-Zernike analysis the critical exponents , and are determined. It suggests that pure SBN61 belongs to the 3D Ising universality class. Doping with Ce
3+
ions, which seem to act as random fields, enhances the relaxor properties. The critical exponents and of SBN61:Ce shift against those of the three-dimensional random-field Ising model.
Received 1 October 1999 相似文献
18.
M. Takigawa M. Ichioka K. Machida 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):303-311
Thermal conductivity κ
xx(T) under a field is investigated in d
x2 - y2-wave superconductors and isotropic s-wave superconductors by the linear response theory, using a microscopic wave function of the vortex lattice states. To study
the origin of the different field dependence of κxx(T) between higher and lower temperature regions, we analyze the spatially-resolved thermal conductivity around a vortex at
each temperature, which is related to the spectrum of the local density of states. We also discuss the electric conductivity
in the same formulation for a comparison.
Received 8 December 2001 and Received in final form 20 March 2002 Published online 6 June 2002 相似文献
19.
J.P. Zagorodny Y. Gaididei F.G. Mertens A.R. Bishop 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):471-487
We investigate the dynamics of out-of-plane (OP) vortices, in a 2-dimensional (2D) classical Heisenberg magnet with a weak
anisotropy in the coupling of z-components of spins (easy plane anisotropy), on square lattices, under the influence of a rotating in-plane (IP) magnetic
field. Switching of the z-component of magnetization of the vortex is studied in computer simulations as a function of the magnetic field's amplitude
and frequency. The effects of the size and the anisotropy of the system on the switching process are shown. An approximate
dynamical equivalence of the system, in the bulk limit, to another system with both IP and OP static fields in the rotating reference frame is demonstrated, and qualitatively the same switching and critical behavior is obtained
in computer simulations for both systems. We briefly discuss the interplay between finite size effects (image vortices) and
the applied field in the dynamics of OP vortices. In the framework of a discrete reduced model of the vortex core we propose a mechanism for switching the vortex polarization, which can account qualitatively
for all our results. A coupling between the IP movement (trajectories) of the vortex center and the OP core structure oscillations,
due to the discreteness of the underlying lattice, is shown. A connection between this coupling and our reduced model is made
clear, through an analogy with a generalized Thiele equation.
Received 6 June 2002 / Received in final form 4 November 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: juan.zagorodny@uni-bayreuth.de 相似文献
20.
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