共查询到20条相似文献,搜索用时 31 毫秒
1.
K. Hagdorn D. Hohlwein J. Ihringer K. Knorr W. Prandl H. Ritter H. Schmid Th. Zeiske 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):243-254
Ho0.1Ca0.9MnO3 is a canted antiferromagnet with the magnetic space group Pn
'
ma
'. The magnetic structure is a superposition C
x
F
y
A
z of the three types of order allowed in Pn
'
ma
'. In the Ca-rich corner of the system Ho
1-x
Ca
x
MnO
3
the title compound has a strong magnetoelastic distortion , the highest metallic conductivity and a ferromagnetic component F
y close to the maximum in the series. Among the areas ab, bc, ca calculated from the lattice constants only ca shows a strong magnetoelastic effect below T
N
= 106
K. The x-, y-, z-spin components depend differently on the temperature. This gives rise to spin rotation which is particularly strong close
to T
N. MnO
6
octahedra have short bond lengths with a temperature independent average . They are practically regular at room temperature and show a Jahn-Teller distortion of 3.5% in the magnetically ordered state.
Above T
N we find small polaron conductivity. The presence of the Jahn-Teller distortion due to the only small abundance (10%) of Mn
3+
in the t
2g
3
e
g configuration is attributed to delocalised e
g electrons. In the magnetically ordered state the averaged magnetic moment of Mn is reduced appreciably from the paramagnetic
value due to spin disorder.
Received 21 January 1999 相似文献
2.
P. Pellegrini O. Dulieu F. Masnou-Seeuws 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):77-86
This paper proposes a general method to investigate Feshbach resonances in atomic collisions similar to Cs(6
s
) + Cs(6
p
) in the thermal or cold regime. In order to compute the predissociation widths of the C
1
Π
u
(6
s
+ 5
d
) bound vibrational levels of Cs2, coupled both with the (2)
3
Σ
+
u
(6
s
+ 6
p
) continuum and with the (2)
3
Π
u
(6
s
+ 5
d
) vibrational series, a Fourier grid method is implemented, with an optical potential. A convenient way of optimizing the latter
is proposed. A large number of resonances are found and calculations of their cross-sections for stabilization into ground
state molecules show that the rate may be important. This confirms the interpretation of Lintz and Bouchiat [Phys. Rev. Lett.
80, 2570 (1998)] who observed dimer formation in cell experiments. Possible generalization to the cold regime relies on the
possibility to tune the position of a resonance to coincide with the maximum of the collisional energy distribution.
Received 14 February 2002 Published online 28 June 2002 相似文献
3.
H.A. Radovan H.H. Wen P. Ziemann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):533-540
Using a specially designed SQUID magnetometer we measured the temperature dependence of the critical current density in a
ring patterned thin film for magnetic fields parallel to the c-axis. In addition, the temporal relaxation of the remanent state as prepared by field cooling in an external field of 100
Oe at different temperatures is determined. The j
c
(
T
) data show a field-dependent anomalous kink close to Tc pointing to reduced dissipation with increasing temperature allowing to construct a corresponding H-T borderline. A similar behavior is observed for the normalized relaxation rate S
(
T
) as extracted from the temporal behavior of the remanent state, which, at low temperatures, exhibits the expected increase
for increasing T-values, while an anomalous decrease of S
(
T
) is found for temperatures above 85 K. While the low-T regime is attributed to creep of 2D pinned single vortex lines, the high-T behavior is suggested to be dominated by collective motion with a more sluggish dynamics. This change in dynamics is also
reflected by the activation barriers for flux creep U
(
j
), which show a corresponding crossover in μ from 0.06 to 0.99. An additional scaling analysis of the E-j characteristics for according to vortex glass theory reveals quasi-2D collective creep behavior with .
Received: 8 April 1998 / Revised: 15 July 1998 / Accepted: 2 September 1998 相似文献
4.
M. Bokor T. Marek K. Tompa P. Gütlich A. Vértes 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(4):567-571
19
F and
11
B spin-lattice relaxation times were measured in [
Zn
(
ptz
)
6
] (
BF
4
)
2
and in the spin-crossover compound [
Fe
(
ptz
)
6
] (
BF
4
)
2
. For both compounds BF
4
-
anion reorientation is active above 50 K. For [
Zn
(
ptz
)
6
] (
BF
4
)
2
, the anion-reorientation dynamics is different in the temperature regions of 50-90 K, 90-120 K, and above 150 K; between
120 and 150 K it changes rapidly reflecting a structural change. In [
Fe
(
ptz
)
6
] (
BF
4
)
2
the mechanism for the paramagnetic relaxation involving the
19
F nuclei is found to be of the diffusion-limited type according to the theory of Lowe and Tse. The present results prove that
the spin-crossover takes place in a dynamic surrounding and not in a static crystal lattice.
Received 09 February 1999 and Received in final form 14 June 1999 相似文献
5.
H. Lippert V. Stert L. Hesse C.P. Schulz W. Radloff I.V. Hertel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):445-448
The H atom transfer reaction in electronically excited indole(NH
3
)
n
clusters is studied in pump-probe experiments with femtosecond laser pulses. By applying different probe photon energies
we are able to detect the dissociation products (NH
3
)
n - 1
NH
4
for n
= 1-6. Furthermore we show that the analysis of the corresponding ion signals is not distorted by contributions from larger cluster
ions due to evaporation of NH
3
molecules. The formation times of the products are ca. 140ps for n
= 2-4 and about 80ps for n
= 5, 6.
Received 30 April 2002 / Received in final form 29 May 2002 Published online 13 September 2002 相似文献
6.
H. Gayvallet J.-C. Géminard 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):369-375
We have studied the temperature dependent resistivity ρ(
T
) of La2-xSrxCuO4 epitaxial thin films in the doping range 0.045 ⩽
x
⩽ 0.25 in pulsed magnetic fields up to 50 T. The zero-field resistivity ρ(
T
) of these samples in the pseudogap regime, can be scaled onto one single universal curve in a broad temperature range by using
a linear transformation of both temperature and resistivity. The high field data ρ(
T
) reveal a metal to insulator transition (MIT) at low temperatures, well into the overdoped regime. For samples having k
F
l
< 1, with kF the Fermi wave vector and l the mean free path, this low temperature insulating behavior of the resistivity is described by the variable range hopping
conductivity (VRH). For samples with k
F
l
> 1, the divergence follows ρ(
T
) ∼
ln
(1/
T
) or a power law, depending upon the Sr-content. We further found that the residual conductivity at the minimum in ρ(
T
), appearing due to the MIT, follows a linear behavior with respect to the Sr-content. It is argued that the unusual MIT in
compounds with k
F
l
> 1, is most probably associated with the pseudogap and the behavior of charge stripes at low temperatures.
Received 4 January 2002 / Received in final form 7 May 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: liesbet.weckhuysen@fys.kuleuven.ac.be 相似文献
7.
W.J. Zakrzewski 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):217-219
In this talk we introduce a Weierstrass-like system of equations corresponding to CP
N
-1 fields in two dimensions. Then using this representation we introduce a vector in R
N
2-1 and treating this vector as the radius vector of a surface immersed in R
N
2-1 we discuss to what extent the associated metric describes the geometry of the CP
N
-1 maps. We show that for the holomorphic maps - the correspondence is exact; while for the more general fields we have to go
beyond the Weierstrass system and add extra terms.
Received 1st August 2001 / Received in final form 18 October 2001 Published online 2 October 2002
RID="a"
ID="a"Work done in collaboration with M. Grundland e-mail: w.j.zakrzewski@durham.ac.uk 相似文献
8.
D. Ashkenasi S. Kröger H.-D. Kronfeldt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(2):197-205
The isotope shift (IS) and hyperfine structure (hfs) of nine levels (31720 to 38921 cm-1) assigned to the configuration 4
f
12
6
s
7
s in neutral erbium have been determined experimentally using Doppler-reduced saturation absorption spectroscopy in a gas discharge.
We performed a fine structure analysis in the SL-coupling scheme of the single configuration 4
f
12
6
s
7
s, confirming and extending the classification of even parity Er I levels. We discriminated the different hfs contributions
of the 4f12 core and the (6
s
+7
s) outer electrons of the shell in a non-relativistic JJ-coupling approach and in the relativistic effective tensor operator formalism in SL-coupling. The relativistic one-electron parameters of the hfs for 167Er were fitted to the experimental data by a least squares fit procedure: [0pt] a
01
4f
=-147(3) MHz, [0pt] a
10
6s
+
a
10
7s
=-1840(30) MHz, [0pt] b
02
4f
=6560(80) MHz. The level dependencies of the isotope shift were evaluated based on crossed second order (CSO) effects. We obtained
the following results for the CSO parameters for the isotope pairs 170-168Er: d
6s7s
=-740(30) MHz, z
4f
= 0(5) MHz, (
g
3,6s
(
f
, 6
s
)+
g
3, 7s
(
f
, 7
s
))= -24(15) MHz and for 170-166Er: d
6s7s
=-1500(50) MHz, z
4f
=0(10) MHz, (
g
3,6s
(
f
,6
s
)+
g
3,7s
(
f
+7
s
))=-50(29) MHz. The resulting parameters for the hfs are compared with those known for other configurations of the Er atom and ion.
Received 16 May 1999 and Received in final form 31 January 2000 相似文献
9.
H. von Löhneysen A. Neubert T. Pietrus A. Schröder O. Stockert U. Tutsch M. Loewenhaupt A. Rosch P. Wölfle 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):447-455
We report on extensive elastic neutron scattering to determine the wave vector of the magnetic order in CeCu6-xAux 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 (0.625
0.275) for x
=0.2, nearly unchanged for x
=0.3, and (0.59) for x
=0.5, staying roughly the same for x
=1.0. In addition, short-range correlations are observed for 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 is close to 2
k
F, where k
F is a typical Fermi momentum.
Received: 20 February 1998 / Accepted: 17 April 1998 相似文献
10.
S.I. Themelis Y. Komninos C.A. Nicolaides 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):277-293
This paper discusses theory and results on 1P0 doubly excited states (DES) in He and in H- of very high excitation, up to the N
= 25 manifold. Our calculations employed full configuration interaction (CI) with large hydrogenic basis sets and produced correlated
wavefunctions for the four lowest roots at each hydrogenic manifold by excluding open channels and the small contribution
of series belonging to lower thresholds. The suitability of the hydrogenic basis sets for such calculations is justified,
apart from their practicality, by the fact that, by computing from them natural orbitals, the results were shown to be the
same with those of earlier multiconfigurational Hartree-Fock (MCHF) calculations on low-lying DES. In total, 160 states were
computed, most of them for the first time. Their energy spectrum should be of use to possible future photoabsorption experiments.
For certain low-lying DES up to N
= 13, for which previous reliable results are available, comparison of the calculated energies shows good agreement. The correlated
wavefunctions contain systematically chosen single and double excitations from each hydrogenic manifold of interest. From
their analysis, we determined the “goodness" of different quantum numbers and the geometry (average angles and radii) as a
function of excitation. For the Sinano lu-Herrick (
K
,
T
) classification scheme, whose basis is a restricted CI with hydrogenic functions and which has thus far been tested only on
low-lying DES, we established that, whereas T remains a good index as energy increases, K does not. Consequently, a more flexible than K quantum number is needed in order to account for most of the additional correlation. This number, represented by F
=
N
-
K
- 1, where N and K are not good numbers anymore, produces consistently a much higher degree of purity than the (
K
,
T
) scheme does, especially as N increases and as the relative significance of various virtual excitations due to electron correlation increases. Among the
four states of each manifold, in all cases in H- and in most cases in He, the three are of the intrashell type and one is of the intershell type with (
F
,
T
) = (0, 0). The lowest intrashell states and the lowest intershell states exhibit a wide angle geometry tending to 180
°
as N
↦∞.
Received 10 September 2001 and Received in final form 12 November 2001 相似文献
11.
Z. Hu M. Knupfer M. Kielwein U.K. Rößler M.S. Golden J. Fink F.M.F. de Groot T. Ito K. Oka G. Kaindl 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):449-453
A strong anisotropic distribution of the holes in Ni 3
d and O 2
p orbitals is observed in the polarization dependent O 1
s and Ni 2
p
3/2
X-ray absorption spectroscopy of the linear-chain nickelate Y2-xCaxBaNiO5 (x
= 0, 0.05, 0.1, 0.2), which demonstrates the one-dimensional nature of the electronic state in these compounds. The holes introduced
by Ca-doping occupy both O 2
p and Ni 3
d orbitals along the NiO5 chains. By comparing the experimental Ni 2
p
3/2
absorption spectra of Y2-xCaxBaNiO5 to those from charge transfer multiplet calculations we can derive the orbital character of the additional holes to be of
∼60% O2
p and ∼40% Ni 3
d.
Received 7 January 2002 相似文献
12.
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
13.
V. Skumryev F. Ott J. M. D. Coey A. Anane J. -P. Renard L. Pinsard-Gaudart A. Revcolevschi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):401-406
The magnetic properties of (
La
1-x
Sr
x
)
MnO
3
crystals have been studied. The ac susceptibility has been measured at frequencies ranging from 10 Hz to 1 000 Hz. The x
= 0.25 crystal shows a typical ferromagnetic behaviour with a dimensionless SI susceptibility of 6 below T
c
= 350
K limited by the demagnetizing field. Both x
= 0 and x
= 0.06 crystals show very sharp peaks in and at the Néel points, 139 K and 135 K respectively. This is quite unlike the usual behaviour of an antiferromagnet. Magnetization
measurements on an untwinned single crystal of LaMnO
3
show a weak moment of at 4.2 K which is directed along the c axis. The origin of this canted antiferromagnetic structure is discussed in terms of anisotropy and of Dzyaloshinskii-Moriya
interaction. It is concluded that anistropy is insufficient to explain the canted antiferromagnetism.
Received 8 January 1999 相似文献
14.
Y. Luspin D. De Sousa Meneses P. Simon G. Hauret 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):215-221
The elastic properties of Cs3H
(
SeO4
)
2
are investigated by Brillouin spectroscopy in the temperature range 20-220 covering the two transitions III II and II I occurring at and , respectively. Phase I is known to be a protonic conductive one. Discontinuities of elastic constants are generally observed
at both transitions, implying first orderness. In phases II and I, a slight broadening of the Brillouin lines is detected.
The results are discussed in comparison with compounds of the families XHSeO4 (X
=
NH4, Rb and Cs) and CsH2BO4 (B
=
As and P) which also undergo a transition to a superionic phase. In the conductive phase, it appears that the lattice anharmonicity
is weaker in Cs3H
(
SeO4
)
2
than in these other compounds.
Received 16 October 1998 相似文献
15.
16.
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
17.
L.A. Errico M. Rentería A.F. Pasquevich A.G. Bibiloni K. Freitag 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(2):149-156
The time-differential-perturbed γ-γ angular-correlation technique (TDPAC) with ion-implanted 181Hf tracers has been applied to study the hyperfine interactions of 181Ta impurities in the cubic bixbyite structure of Er
2
O
3
and Gd
2
O
3
. The TDPAC experiments were performed in air in the temperature range 300-1073 K (in the case of Er
2
O
3
) and 300-1173 K (in the case of Gd
2
O
3
). Three electrical-quadrupole interactions were found in each oxide in the whole studied temperature range. Two of them were
attributed to the electric-field gradients (EFG) acting on 181Ta probes substitutionally located on the two nonequivalent free-of-defects cation sites of the bixbyite structure. The EFG
results are compared with predictions of the point-charge model and discussed together with previous results obtained with
the probes 111Cd and 181Ta in other isomorphous sesquioxides. The temperature dependence of the hyperfine parameters for both oxides is also discussed
in terms of dilatometric expansion data.
Received 29 December 2000 and Received in final form 8 March 2001 相似文献
18.
19.
T. Koga H. Matsuyama J. Molina Molina J.S. Dehesa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(1):17-23
Electron-pair intracule (relative motion) and extracule (center-of-mass motion) densities are studied in both position and
momentum spaces for the
1
P and
3
P terms of the group 2 atoms Be (atomic number Z
=4), Mg (Z
=12), Ca (Z
=20), Sr (Z
=38), Ba (Z
=56), and Ra (Z
=88). In position space, the
1
P
-
3
P difference in the intracule densities shows that the probability of a small interelectronic distance is larger in the triplet
for all the six atoms, as reported for the lightest Be atom in the literature. The position-space extracule density clarifies
that the triplet electrons are more likely to be at opposite positions with respect to the nucleus than the singlet electrons
for all the atoms. In momentum space, the singlet generally has a larger probability of a small relative momentum between
two electrons as a na?ve manifestation of the Fermi hole in the triplet. The extracule density in momentum space shows that
the
1
P term has a distribution larger in a large center-of-mass momentum region than the
3
P term.
Received: 26 August 1998 / Received in final form: 1 February 1999 相似文献
20.
N. Magneron Y. Luspin G. Hauret E. Philippot 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):7-15
Transverse and pseudo-transverse elastic waves have been studied in several scattering geometries in order to investigate
the temperature dependences of C
E
66
and C
E
14
over the range 300-1100 K, including the transitions near 860 K. These results complete those on C
E
44
we have obtained in a previous work. All these constants display discontinuities at the lock-in transition. In the phase, the results are analysed in term of lowest order couplings between strains (e) and the order parameter (Q). The main features are described by the lowest order biquadratic e2Q2 coupling, in particular for C
E
44
in a large temperature range. However, it appears that a contribution of the next coupling term arises for C
E
66
below K and that the first two lowest order terms have to be taken into account even just below the lock-in transition in the case
of C
E
14
. The temperature dependence of Q has been deduced and it can be well described in the framework of Landau's theory.
Received: 2 October 1997 / Received in final form: 3 December 1997 / Accepted: 29 January 1998 相似文献