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1.
M.I. Marqués J.A. Gonzalo 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):317-321
The Monte Carlo (MC) approach is used to check the validity of the scaling relationship for the effective critical exponents in thin Ising films. We investigate this relationship not just in the critical region
but throughout the crossover to the expected two-dimensional behavior. Our results indicate that this scaling relationship
is very well-fulfilled throughout the entire crossover temperature region, as predicted by a previous renormalization group
analysis. The two-dimensional universality class of Ising films is confirmed by means of data collapsing plots for plates with increasing L, up to L=100. The evolution of the maximum value of the effective critical exponents with film thickness is discussed.
Received 22 April 1999 相似文献
2.
D. Görlitz J. Kötzler 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):37-43
Between 4.2 K and the Curie temperatures of the cubic Heisenberg ferromagnets EuS and EuO, their homogeneous dynamic susceptibilities
have been investigated by means of a broad-band reflectometer operating from 0.1 GHz to 40 GHz. For internal magnetic fields
larger than the anisotropy fields H
A
(
T
) of both materials, their static susceptibilities exhibit a -divergence, which reveals quantitatively the dominance of dipolar-anisotropic spin-wave fluctuations. displays a Lorentzian shape the damping frequency of which obeys scaling in terms of .The scaling function agrees quantitatively with work by Frey and Schwabl [#!FS88!#] for dipolar Heisenberg ferromagnets at
temperatures above Tc. Building upon their approach, the resonance frequency of the Lorentzian can be related to a memory effect in the damping
determined by the large value of the relaxation rate of the longitudinal magnetization fluctuations . For EuS, this relation is substantiated directly by inelastic neutron scattering. All these features reveal the hitherto
uncovered importance of the dipolar anisotropic fluctuations below Tc of ferromagnets.
Received: 4 March 1998 / Accepted: 12 May 1998 相似文献
3.
M. Stenger S. Baumhoff J.-Y. Prieur J. Joffrin J.-P. Contour 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):177-182
We present measurements of the attenuation and phase velocity of surface acoustic waves in thin YBa2Cu3O films as a function of temperature, in magnetic fields up to 3.6 T applied parallel to the c-axis of the films. We have observed anomalies in both, the attenuation and the phase velocity in the vicinity of the superconducting
critical temperature which do not depend on the magnetic field. Possible origins of these anomalies, observed, to our knowledge,
for the first time in YBa2Cu3O thin films, are discussed and compared to bulk acoustic wave experiments. We present a kind of feedback technique for surface
acoustic waves which improves the sensitivity of this type of measurement. The actual sensitivity limits are mentioned.
Received: 7 August 1997 / Revised: 7 November 1997 / Accepted: 17 November 1997 相似文献
4.
X.S. Chen V. Dohm D. Stauffer 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):699-704
Using field theory and Monte Carlo (MC) simulation we investigate the finite-size effects of the magnetization M for the three-dimensional Ising model in a finite cubic geometry with periodic boundary conditions. The field theory with
infinite cutoff gives a scaling form of the equation of state where is the reduced temperature, h is the external field and L is the size of system. Below and at the theory predicts a nonmonotonic dependence of f(x,y) with respect to at fixed and a crossover from nonmonotonic to monotonic behaviour when y is further increased. These results are confirmed by MC simulation. The scaling function f(x,y) obtained from the field theory is in good quantitative agreement with the finite-size MC data. Good agreement is also found
for the bulk value at .
Received 20 July 1999 and Received in final form 11 November 1999 相似文献
5.
G. Chaboussant M.-H. Julien Y. Fagot-Revurat M. Hanson L.P. Lévy C. Berthier M. Horvatic O. Piovesana 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):167-181
In a magnetic field, spin-ladders undergo two zero-temperature phase transitions at the critical fields Hc1 and Hc2. An experimental review of static and dynamical properties of spin-ladders close to these critical points is presented. The
scaling functions, universal to all quantum critical points in one-dimension, are extracted from (a) the thermodynamic quantities
(magnetization) and (b) the dynamical functions (NMR relaxation). A simple mapping of strongly coupled spin ladders in a magnetic
field on the exactly solvable XXZ model enables to make detailed fits and gives an overall understanding of a broad class of quantum magnets in their gapless
phase (between Hc1 and Hc2). In this phase, the low temperature divergence of the NMR relaxation demonstrates its Luttinger liquid nature as well as
the novel quantum critical regime at higher temperature. The general behavior close these quantum critical points can be tied
to known models of quantum magnetism.
Received: 13 March 1998 / Received in final form and Accepted: 21 July 1998 相似文献
6.
Universal non-monotonic smectic fluctuations of liquid crystal films in a magnetic field 总被引:1,自引:0,他引:1
I.N. de Oliveira M.L. Lyra 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):189-194
Free-standing liquid crystal films with positive diamagnetic susceptibility can have the smectic ordering enhanced by an external
field applied perpendicular to the plane layers. Within a quadratic functional integral approach, we investigate the interplay
between the smectic order induced by an external field H and that due to the surface tension γ between the film and the surrounding gas. We find that the average smectic fluctuation
is a non-monotonic function of film thickness, with a characteristic thickness scale ξ
H delimiting the predominance of surface tension and magnetic field effects. This characteristic thickness obeys simple asymptotic
power-law relations as a function of the ordering terms which allows us to represent the average smectic fluctuations in a
universal scaling form.
Received 7 January 2003 Published online 1st April 2003
RID="a"
ID="a"e-mail: marcelo@ising.fis.ufal.br 相似文献
7.
X.S. Chen V. Dohm 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):687-703
We reexamine the range of validity of finite-size scaling in the lattice model and the field theory below four dimensions. We show that general renormalization-group arguments based on the renormalizability of
the theory do not rule out the possibility of a violation of finite-size scaling due to a finite lattice constant and a finite
cutoff. For a confined geometry of linear size L with periodic boundary conditions we analyze the approach towards bulk critical behavior as at fixed for where is the bulk correlation length. We show that for this analysis ordinary renormalized perturbation theory is sufficient. On
the basis of one-loop results and of exact results in the spherical limit we find that finite-size scaling is violated for
both the lattice model and the field theory in the region . The non-scaling effects in the field theory and in the lattice model differ significantly from each other.
Received 5 February 1999 相似文献
8.
W. Dahle W. Göpel U. Gradmann K. Salewski 《Applied Physics A: Materials Science & Processing》1977,13(3):239-244
Ferromagnetic resonance (FMR) and torsion magnetometry were carried out on 60 Ni/40 Fe (111) oligatomic thin films (2.4≦D
M≦9.4 atomic layers) at temperatures between 123 K and 373 K. A comparative discussion of the results is given. Anisotropies
of the films, determined by both methods, agree roughly. Approximately, they show a 1/D
M-dependence on the film thickness, as expected from an interpretation as surface anisotropy. FMR is shown to be a useful experimental
tool for the investigation of oligatomic ferromagnetic films. Informations may be taken from the resonance field, line width,
line shape and total absorbed microwave power. The magnetic moment must be taken from magnetometry. 相似文献
9.
J. Corno M. Galtier D. Renard J.P. Renard F. Trigui 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):223-231
We report here on resistance and magnetoresistance (MR) studies of ultrathin Co/Au(111) single sandwiches and bilayers with
perpendicular magnetization. Resistance of the films was measured in situ in ultrahigh vacuum, during depositions and as a function of a perpendicular applied magnetic field. A large MR variation
with the thickness of Au coverage was observed and compared to calculations. The coercive field of the Co films shows a drastic
variation with the Au coverage thickness, which reflects the theoretical anisotropy variation. It was measured as a function
of temperature. For the first time, the effect of interlayer interaction on the resistivity of a Co bilayer during the growth
of Co top layer, is evidenced and compared to calculations. Finally, hysteresis loops of strongly antiferromagnetically coupled
bilayers are investigated.
Received 3 November 1998 and Received in final form 18 January 1999 相似文献
10.
T. Schneider J. Hofer M. Willemin J.M. Singer H. Keller 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):413-416
Anisotropic Ginzburg-Landau superconductors of extreme type-II are considered in an approximation where magnetic field fluctuations
are neglected. A formulation of the scaling properties is presented for the singular part of the free energy density in the
presence of a magnetic field. From the existence of a magnetization, a diamagnetic susceptibility and superconductivity we
determine the limiting behavior of the scaling function in the vicinity of the zero field transition temperature, where critical
fluctuations dominate. Our predictions for the temperature and field dependence of magnetization, magnetic torque and melting
line etc., uncover the universal critical properties and provide an extension of hitherto used mean-field treatments. The results are
consistent with experimental data.
Received: 24 April 1998 / Accepted: 5 May 1998 相似文献
11.
H. Beckmann G. Bergmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):495-502
Sandwiches made from Fe and Cs films are investigated as a function of the magnetic field and the Cs thickness. Conduction
electrons which cross from the Fe to the Cs are marked by a drift velocity component perpendicular to the electric field.
The anomalous Hall effect in the Fe provides this “non-diagonal” kick to the electrons that cross from the Fe into the Cs.
The ballistic propagation of the conduction electrons can be monitored as a function of the Cs film thickness. The free propagation
into the Cs is measured in terms of the non-diagonal conductance Lxy which we denote as the “induced anomalous Hall conductance”L
xy
0. For a normal (non-magnetic) metal in contact with Fe, Lxy increases with the thickness of the normal metal until the film thickness exceeds (half) the mean free path of the conduction
electrons. For Cs on top of Fe the induced anomalous Hall conductance increases up to a Cs coverage of about 100 A, then,
in contrast to other non-magnetic metals, L
xy
0 decreases for larger Cs coverage and approaches zero. This behavior cannot be explained with the free electron model. The
strange behavior of the induced AHC in Cs films adds an even more challenging mystery to the already poorly understood properties
of thin Cs films. These results defy explanation in the free electron model.
Received 29 April 1999 and Received in final form 10 July 1999 相似文献
12.
F. Pérez-Willard A. Faißt J. Wosnitza H.. v. Löhneysen U. Schotte H. Tanaka 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):247-251
We report on the magnetic phase diagram of the distorted triangular-lattice antiferromagnet RbCuCl3 for a magnetic field applied parallel to the basal plane (). High-resolution measurements of the specific heat and of the magnetocaloric effect have been performed in magnetic fields
up to 14 T. The high-field specific-heat data reveal the existence of an intermediate phase between the paramagnetic and the
frustrated antiferromagnetic phase.
Received 18 October 1999 相似文献
13.
B. Dubrulle 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):757-771
We develop a new approach to scale symmetry, which takes into account the possible finite cut-offs of the fields or the parameters.
This new symmetry, called finite size scale symmetry: i) includes the traditional self-similarity as a limiting case, when
the cut-offs are set to infinity (infinite size-system); ii) is consistent with the traditional finite size scaling approach
already used in critical phenomena; iii) enables the computation of some of the universal functions appearing in the finite
size scaling formulation; iv) allows scale transformations leaving the cut-offs invariant, like in the traditional renormalization
approach; v) can be formulated to allow for positive or negative fields and parameters; vi) leads to new predictions about
the shape of some distributions in critical phenomena or turbulence which are in very good agreement with the experimental
or numerical findings.
Received 26 January 1999 and Received in final form 25 October 1999 相似文献
14.
D. Hinzke U. Nowak D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):435-438
We simulated the field-dependent magnetization m(H,T) and the uniform susceptibility of classical Heisenberg antiferromagnets in the chain and square-lattice geometry using Monte Carlo methods. The results
confirm the singular behavior of at small T,H: and , where D=3 is the number of spin components, J
0=zJ, and z is the number of nearest neighbors. A good agreement is achieved in a wide range of temperatures T and magnetic fields H with the first-order 1/D expansion results (D.A. Garanin, J. Stat. Phys. 83, 907 (1996)).
Received 20 March 2000 相似文献
15.
F. Schinagl H. Iro R. Folk 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):113-123
Within mean field approximation we investigate the phase diagrams of magnetic fluids in presence of a magnetic field. In a
finite field the magnetic phase transition is absent, but instead a line of first order liquid-liquid transitions ending in
a critical point occurs for a magnetic interaction, which is sufficiently strong. Varying the magnetic field these critical
points extend from the tricritical point at H=0 to a critical endpoint. For a fluid with Ising spins we calculate the critical lines and several tricritical exponents
analytically. For Heisenberg fluids we obtain the phase diagrams from a numerical solution of the mean field equations of
state.
Received 20 March 1998 相似文献
16.
C. Ferdeghini V. Ferrando V. Braccini M.R. Cimberle D. Marré P. Manfrinetti A. Palenzona M. Putti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):147-151
The anisotropy of MgB2 is still under debate: its value, strongly dependent on the kind of sample and on the measuring method, ranges between 1.2
and 13. In this work we present our results on MgB2 c-oriented superconducting thin film. To evaluate the anisotropy, we followed two different approaches. Firstly, magnetoresistivity
was measured as a function of temperature at selected magnetic fields applied both parallel and perpendicular to the c-axis; secondly, we measured magnetoresistivity at selected temperatures and magnetic fields, varying the angle θ between the magnetic field and the c-axis. The anisotropy estimated from the ratio between the upper critical fields parallel and perpendicular to the c-axis and the one obtained in the framework of the scaling approach within the anisotropic Ginzburg-Landau theory are different
but show a similar trend in the temperature dependence. Some differences in the upper critical field and in its anisotropy
of our film with respect to single crystals are emphasized: some of these aspects can be accounted for by an analysis of upper
critical fields within a two-band model in presence of disorder and/or crystallographic strain.
Received 12 July 2002 / Received in final form 17 September 2002 Published online 29 November 2002 相似文献
17.
T. Emig T. Nattermann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):525-546
The simultaneous effect of both disorder and crystal-lattice pinning on the equilibrium behavior of oriented elastic objects
is studied using scaling arguments and a functional renormalization group technique. Our analysis applies to elastic manifolds,
e.g., interfaces, as well as to periodic elastic media, e.g., charge-density waves or flux-line lattices. The competition between both pinning mechanisms leads to a continuous, disorder
driven roughening transition between a flat state where the mean relative displacement saturates on large scales and a rough
state with diverging relative displacement. The transition can be approached by changing the impurity concentration or, indirectly,
by tuning the temperature since the pinning strengths of the random and crystal potential have in general a different temperature
dependence. For D dimensional elastic manifolds interacting with either random-field or random-bond disorder a transition exists for 2<D<4, and the critical exponents are obtained to lowest order in . At the transition, the manifolds show a superuniversal logarithmic roughness. Dipolar interactions render lattice effects
relevant also in the physical case of D=2. For periodic elastic media, a roughening transition exists only if the ratio p of the periodicities of the medium and the crystal lattice exceeds the critical value . For p<p
c
the medium is always flat. Critical exponents are calculated in a double expansion in and and fulfill the scaling relations of random field models.
Received 28 August 1998 相似文献
18.
W. Westerburg F. Martin P.J.M. van Bentum J.A.A.J. Perenboom G. Jakob 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):509-513
We measured the temperature dependence of the linear high field Hall resistivity of ( K) and ( K) thin films in the temperature range from 4 K up to 360 K in magnetic fields up to 20 T. At low temperatures we find a
charge-carrier density of 1.3 and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In this temperature
range electron-magnon scattering contributes to the longitudinal resistivity. At the ferromagnetic transition temperature
a dramatic drop in the number of charge-carriers n down to 0.6 holes per unit cell, accompanied by an increase in unit cell volume, is observed. Corrections of the Hall data
due to a non saturated magnetic state will lead a more pronounced charge-carrier density collapse.
Received 22 July 1999 and Received in final form 7 October 1999 相似文献
19.
The critical behaviour of thin films containing quenched random impurities and inhomogeneities is investigated by the renormalization-group method to the one-loop order within the framework of the n-component φ4-model. The finite-size crossover in impure films has been considered on the basis of the fundamental relationship between the effective dimensionality Deff and the characteristic lengths of the system. The fixed points, their stability properties and the critical exponents are obtained and analyzed, using an
-expansion near the effective spatial dimensionality Deff of the fluctuation modes in D-dimensional hyperslabs with two types of quenched impurities: point-like impurities with short-range random correlations and extended (linear) impurities with infinite-range random correlations along the small-size spatial direction. The difference between the critical properties of infinite systems and films is demonstrated and investigated. A new critical exponent, describing the scaling properties of the thickness of films with extended impurities has been derived and calculated. A special attention is paid to the critical behaviour of real impure films (D=3). 相似文献
20.
T. Kerle J. Klein K. Binder 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):401-410
The capillary broadening of a 2-phase interface is investigated both experimentally and theoretically. When a binary mixture
in a thin film with thickness D segregates into two coexisting phases the interface between the two phases may form parallel to the substrate due to preferential
surface attraction of one of the components. We show that the interfacial profile (of intrinsic width w0) is broadened due to capillary waves, which lead to fluctuations, of correlation length of the local interface positions in the directions parallel to the confining walls. We postulate that acts as an upper cutoff for the spectrum of capillary waves on the interface, so that the effective mean square interfacial
width w varies as . In the limit of large D this yields or respectively for the case of short- or long-range forces between walls and the interface. We used the Nuclear Reaction Analysis
depth profiling technique, to investigate this broadening effect directly in two binary polymer mixtures. Our results reveal
that the interfacial width indeed increases with film thickness D, though the observed interfacial width is lower than the predicted w. This is probably due to surface tension effects imposed by the confining surfaces which are not taken into account in our
model.
Received: 19 February 1998 / Received in final form: 2 September 1998 / Accepted: 8 September 1998 相似文献