共查询到20条相似文献,搜索用时 359 毫秒
1.
M. Zazo L. Torres J. Iñiguez J. M. Muñoz C. de Francisco 《Applied Physics A: Materials Science & Processing》1993,57(3):239-242
The time dependence of the field-cooled susceptibility in polycrystalline samples of YBa2Cu3O7 has been studied in the temperature range 77–95 K. Field-cooled and zero-field-cooled susceptibility measurements and its variation with the ac magnetic field are also reported. Measurements have been carried out by means of an inductive technique. Our fully automatic system allows us to measure the first data points of field-cooled susceptibility versus time from the beginning of the magnetic relaxation just after removing the field. 相似文献
2.
A. Paolone P. Roy A. Pimenov A. Loidl A.A. Mukhin A.M. Balbashov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):245-250
The optical conductivity of La0.85Sr0.15MnO3 single crystals was studied by means of submillimeter and infrared spectroscopy for frequencies cm-1 and temperatures 10 K <
T
<300 K. The submillimeter conductivity follows the temperature dependence of the dc-data. The phonon spectrum of La0.85Sr0.15MnO3 changes considerably below K revealing a structural phase transition induced by charge or orbital order. At T
=10 K a number of phonon modes can be identified in addition to the room-temperature spectrum. The optical conductivity () in the mid-infrared reveals the characteristics of small polaron absorption. Below the magnetic ordering temperature the
polaron binding energy is highly reduced, but the onset of charge order interrupts the formation of free charge carriers with
a Drude-like behavior. The frequency and temperature dependence of in this regime qualitatively resembles the small polaron predictions by Millis et al. (Phys. Rev. B 54, 5405 (1996)).
Received 5 November 1999 相似文献
3.
Transition to Fulde-Ferrel-Larkin-Ovchinnikov phases near the tricritical point: an analytical study
R. Combescot C. Mora 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):397-406
We explore analytically the nature of the transition to the Fulde-Ferrel-Larkin-Ovchinnikov superfluid phases in the vicinity
of the tricritical point, where these phases begin to appear. We make use of an expansion of the free energy up to an overall
sixth order, both in order parameter amplitude and in wavevector. We first explore the minimization of this free energy within
a subspace, made of arbitrary superpositions of plane waves with wavevectors of different orientations but same modulus. We
show that the standard second order FFLO phase transition is unstable and that a first order transition occurs at higher temperature.
Within this subspace we prove that it is favorable to have a real order parameter and that, among these states, those with
the smallest number of plane waves are preferred. This leads to an order parameter with a cos(
.
) dependence, in agreement with preceding work. Finally we show that the order parameter at the transition is only very slightly
modified by higher harmonics contributions when the constraint of working within the above subspace is released.
Received 20 February 2002 / Received in final form 4 June 2002 Published online 13 August 2002 相似文献
4.
Y.N. Ovchinnikov V.Z. Kresin 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):203-209
The pair-breaking effect and its impact on the properties of borocarbides is studied. The pair-breaking effect caused by localized
magnetic moments drastically affects the superconducting properties. Interaction between the magnetic moments and the resulting
ordering trend lead to a behavior entirely different from the conventional picture. The main focus is on the behavior of the
upper () and lower () critical fields. In addition, the temperature dependence of several quantities (penetration depth, coherence length, etc.)
has been calculated. The theory has been applied to the borocarbide LuNi2B2C and is in very good agreement with the recent experimental data.
Received 29 June 1999 相似文献
5.
B. Andraka R. Pietri S.G. Thomas G.R. Stewart E.-W. Scheidt T. Schreiner 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):55-59
A comprehensive study of the relationship between the electronic specific heat coefficient () and the temperature square coefficient (A) of the electrical resistivity for a single, cubic, heavy fermion alloy system, UPt5-xAux is presented. In this alloy system, whose low temperature properties are consistent with the Fermi-liquid behavior, varies by more than a factor of 10 while the corresponding A coefficient changes by a factor larger than 200. A tracks changes in fairly well, but , postulated to have a universal value for heavy fermions, is not constant and varies from about 10-6 (x = 0, 0.5) to 10-5
cm (mol K/mJ)2 (x
> 1.1), thus from a value typical of transition metals to that characteristic of other heavy fermion compounds. We have found a
correlation between and magnetic characteristics such as the paramagnetic Curie-Weiss temperature and the low temperature magnetic susceptibility
divided by .
Received 29 January 1999 相似文献
6.
The frequency dependence of the ac susceptibility for an aluminosilicate glass containing 14.3 at% cobalt has been measured over six decades in frequency. A very strong frequency dependence of χ(T) is observed both around and below the freezing temperature in contrast to the transition metal spin glasses. Possible reasons for these differences are discussed. 相似文献
7.
A. Volmer M. Schwartz 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):211-218
In pure anisotropic or layered superconductors thermal fluctuations induce a van der Waals attraction between flux lines.
This attraction together with the entropic repulsion has interesting consequences for the low field phase diagram; in particular,
a first order transition from the Meissner phase to the mixed state is induced. We introduce a new variational approach that
allows for the calculation of the effective free energy of the flux line lattice on the scale of the mean flux line distance
a, which is based on an expansion of the free energy around the regular triangular Abrikosov lattice. Using this technique,
the low field phase diagram of these materials may be explored. The results of this technique are compared with a recent functional
RG treatment of the same system.
Received: 25 June 1996 / Revised: 18 August 1998 / Accepted: 21 August 1998 相似文献
8.
9.
Scaling of vortex transport properties and nonlinear ac response of high-temperature superconductors
Y. Wang H.D. Chen D.L. Yin K.X. Chen G. Lu W.P. Bai C.Y. Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):221-225
The macroscopic behavior of high-temperature superconductors is described by a nonlinear response function in combinations
with Maxwell equations. This function is compatible with the suggested different model pinning barriers U(J). A comparison of this function to the scaling behavior of the isothermal current-voltage characteristics measured in twinned
YBa2Cu3O (YBCO) samples shows fair agreement. We also compare the amplitude dependence of ac susceptibility derived from this function
with several experimental results of high-temperature superconductors and find a general power law in the out-of-phase peak shift.
Received 4 August 1999 and Received in final form 30 November 1999 相似文献
10.
11.
P.K. Nayak 《Solid State Communications》2006,138(8):377-381
The temperature and AC field amplitude variations of AC susceptibility have been measured on pure and 5 wt% Ag doped (La1−xYx)2Ba2CaCu5Oz superconductors. The AC susceptibility as a function of field have been analyzed using Kim's critical state model. The temperature dependence of intergranular critical current density and the effective volume fractions of the grains have been estimated. The Ag doped samples show relatively large critical current density due to the improved intergranular coupling. The exponent of temperature variation of critical current density suggests that the weak links form superconductor-normal metal-superconductor (SNS) type of junctions for all the samples. 相似文献
12.
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
13.
A. Schenck N.K. Sato G. Solt D. Andreica F.N. Gygax M. Pinkpank A. Amato 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):245-256
We report on transverse field (TF) Muon Spin Rotation (μSR) measurements on a single crystal of the hexagonal heavy fermion
superconductor UNi2Al3 between 5 K and 300 K. From the measured muon Knight shift (KS) in the easy (
a
,
b
)-plane and along the c-axis we extracted the local magnetic susceptibility tensor [0pt] , which arises from the nearest U-neighbors. By comparison with the bulk susceptibility [0pt] it is found that [0pt] and [0pt] agree well above 150 K but deviate considerably in the basal plane below 150 K, due to the disturbance introduced by the
. We succeed in reproducing both [0pt] and [0pt] on the basis of a crystalline electric field (CEF)-approach assuming U to be in the tetravalent state. The disturbance introduced by the affects the CEF-Hamiltonian in an expected manner, suggesting strongly that a CEF-picture implying a rather local 5
f-electron wave function is indeed valid. Reanalyzing older data on UPd2Al3 we arrive at the same conclusion. A necessary condition for extracting the local susceptibility was the knowledge of the
-site, this information was derived from the analysis of the TF-relaxation rates. At low temperatures we found about 30% of
the implanted at the d-site and none at this site above 200 K. The majority fraction was found to be in a tunneling state over six m (or k)-sites around the b-site. No long range diffusion was seen up to room temperature.
Received 20 April 1999 相似文献
14.
S. Garcia L. Ghivelder S. Soriano I. Felner 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(3):307-313
The magnetic properties of the superconducting ruthenate-cuprate RuSr2Eu
1.4Ce0.6Cu2O10-δ (Ru-1222) have been studied by a
scaling analysis of the dc magnetization and ac susceptibility measurements.
Non-linear M(H) curves reveal the presence of nano-size clusters with a
net magnetic moment of ∼102 μB at 180 K, near the
deviation from a Curie-Weiss behavior. On cooling, no scaling was observed
down to 90 K, discarding the possibility of magnetic phase separation of
collinear ferromagnetic particles. We explain this result in terms of a
variable number of contributing particles, with a temperature dependent net
magnetic moment. For 70 K ≤T≤ 90 K the scaling plots evidence the
emergence of a system of non-interacting particles, which couple on further
cooling. The observed cluster-glass features are preserved down to the
lowest measured temperature (10 K); no signature of long-range order was
detected. The frequency shift of the peak in the real part of the ac
susceptibility does not follow the Vogel-Fulcher type dependence, as
previously reported. The puzzling temperature dependence of the coercive
field, HC(T), is correlated with the changes in the scaling factors. 相似文献
15.
Ph. Brune A.P. Kampf 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):241-245
We apply a diagrammatic expansion method around the atomic limit () for the U-t-t
' Hubbard model at half filling and finite temperature by means of a continued fraction representation of the one-particle
Green's function. From the analysis of the spectral function we find an energy dispersion relation with a modulation of the energy gap in the insulating phase. This anisotropy is compared with experimental ARPES results on insulating
cuprates.
Received 18 May 2000 and Received in final form 9 August 2000 相似文献
16.
C. Stockinger G. Heine W. Markowitsch W. Lang R. Adam R. Sobolewski R. Rössler J.D. Pedarnig D. Bäuerle 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):227-231
() thin films were photodoped with white light at various temperatures from 70 K to 290 K. Before and after the excitation,
the magnetoconductivity was measured in a magnetic field B
= 0.5 T, and the experimental results were fitted to the Aslamazov-Larkin theory of superconducting order-parameter fluctuations
to determine the superconducting coherence lengths, and . We observed that the photodoping process enhanced and and that the amount increased with the photodoping temperature increase. On the other hand, the superconducting anisotropy
/ decreased with increasing temperature. The photodoping effect enhances superconducting properties of partially oxygen-deficient
samples and is considerably increased by high doping temperatures.
Received 15 December 1999 and Received in final form 24 May 2000 相似文献
17.
YanFei Zhang ChunLei Wang JiChao Li MingLei Zhao JiaLiang Zhang 《Physica B: Condensed Matter》2008,403(17):2822-2827
Dielectric susceptibility and domain evolution of the relaxor ferroelectrics have been simulated using the Monte Carlo method upon the Potts-Ising model. The grain size effect and the applied ac field frequency effect on the dielectric susceptibility were theoretically investigated. We found that the dielectric susceptibility increases and the Tm (the temperature at which the dielectric susceptibility reaches the maximum) shifts to lower temperature with increasing average grain size or decreasing frequency. In addition, we obtained the value of the relaxation parameter γ estimated from the linear fit of the modified Curie-Weiss law; its changing trend with increasing average grain size or increasing frequency was well consistent with the experimental observation. From the results of the domain pattern evolution process, we observed the differences between relaxor ferroelectrics and normal ferroelectrics subjected to an applied ac field. 相似文献
18.
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
19.
Niharika Mohapatra Kartik K. Iyer B.A. Chalke E.V. Sampathkumaran 《Solid State Communications》2009,149(39-40):1641-1645
We have investigated the magnetic behavior of nano crystals, synthesized by high-energy ball-milling, for a well-known geometrically frustrated spin-chain system, Ca3CoRhO6, and compared its magnetic characteristics with those of the bulk form by measuring ac and dc magnetization. The features attributable to the onset of ‘partially disordered antiferromagnetism’ (characterizing the bulk form) are not seen in the magnetization data of the nano particles; the magnetic moment at high fields in the very low temperature range in the magnetically ordered state gets relatively enhanced in the nano particles. It appears that the ferromagnetic intrachain interaction, judged by the sign of the paramagnetic Curie temperature, is preserved in the nano particles. These trends are opposite to those seen in the nano particles of Ca3Co2O6. However, the complex spin-dynamics as evidenced by large frequency dependence of ac susceptibility is retained in the nano particles as well. Thus, there are some similarities and dissimilarities between the properties of the nano particles and those of the bulk. We believe that these findings will be useful to understand correlation lengths deciding various properties of geometrical frustration and/or spin-chain phenomena. 相似文献
20.
S. Paschen E. Felder H.R. Ott 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):169-176
We present measurements of the specific heat, the electrical resistivity, the Hall effect, and the magnetic susceptibility
of CeAuAl3, a new heavy-electron compound that crystallizes in an ordered derivative of the tetragonal BaAl4-type structure. For comparison we have also done some of these measurements on the isostructural non-magnetic reference compound
LaAuAl3, which appears to be a simple metal. Below K, CeAuAl3 orders antiferromagnetically and below 1K, we encounter Fermi liquid behaviour with considerably enhanced effective masses,
i.e., a quadratic temperature dependence of the resistivity with a large prefactor and a sizable linear-in-T contribution to the specific heat. This linear-in-T contribution increases by more than a factor 50 from its value at to its value at . Consequently CeAuAl3 develops a heavy-electron ground state, coexisting with antiferromagnetic order. The small energy scales involved in the
problem make CeAuAl3 a good candidate for tuning it, by varying external parameters, towards a quantum critical point. At high temperatures we
observe local moment behaviour. From the temperature dependence of the magnetic susceptibility and the specific heat we have
derived the crystalline-electric-field-split level scheme of the J
=5/2 multiplet. Distinct features in the electrical resistivity provide additional evidence for this level splitting.
Received: 6 November 1997 / Accepted: 17 November 1997 相似文献