共查询到20条相似文献,搜索用时 31 毫秒
1.
A. Peñaranda C.E. Auguet L. Ramırez-Piscina 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):155-165
The simulation of the transition sequence of superheated Type I superconducting granules (SSG) in disordered suspensions when
an external magnetic field is slowly increased from zero has been studied. Simulation takes into account diamagnetic interactions
and the presence of surface defects. Results have been obtained for the transition sequence and surface fields distribution
covering a wide range of densities. These results are compared with previous analytical perturbative theory, which provides
qualitative information on transitions and surface magnetic fields during transitions, but with a range of validity apparently
limited to extremely dilute samples. Simulations taking into account the complete diamagnetic interactions between spheres
appear to be a promising tool in interpreting SSG experiments, in applications such as particle detectors, and in some fundamental
calculations of Solid State Physics.
Received 6 April 2001 and Received in final form 15 October 2001 相似文献
2.
A. Saber G. Mattei X. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):393-399
Within the framework of the effective field theory with a probability distribution technique that accounts for the single-site
spin correlations, we examine the critical behavior of the transverse ferromagnetic spin-1 Ising model of an alternating magnetic
superlattice. The critical temperature of the alternating magnetic superlattice has been studied as a function of the interlayer
and intralayer exchange interactions and the strength of the transverse field and the thickness of the finite superlattice.
Received 12 January 2000 and Received in final form 14 September 2000 相似文献
3.
F. Delfino R. Procopio M. Rossi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):31-38
The evaluation of the total force of magnetic origin acting upon a body in a stationary magnetic field is often carried out
using the so-called magnetic energy (or co-energy) method, which is based on the derivation of the magnetic energy (or co-energy) with respect to a virtual rigid displacement
of the considered body. The application of this method is usually justified by resorting to the energy conservation principle,
written in terms both of electrical and of mechanical quantities. In this paper we shall re-examine the whole matter in the
context of classical thermodynamics, in order to obtain a more comprehensive and general proof of the validity of the energy
(or co-energy) approach and to point out its limitations. Two typical configurations will be discussed; in the first one,
the field sources are represented by conducting bodies carrying free currents, whereas in the second one a permanent magnet
creates the driving field. All magnetic materials are assumed to be non-hysteretic and permanent magnets are represented by
means of the well-known linear model in the second quadrant of the (B,H) plane.
Received 25 July 2001 and Received in final form 5 November 2001 相似文献
4.
5.
E. Rastelli A. Tassi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):285-289
Dipolar spin-spin interactions play a crucial role as for the magnetic order in the compounds of the RBa2Cu3O6+x family, (R = Dy, Er, Nd). However, inelastic neutron scattering data observed in ErBa2Cu3O7 can be explained only if exchange interactions in addition to dipolar ones are taken into account.
Received: 12 January 1998 / Received in final form: 26 March 1998 / Accepted: 10 April 1998 相似文献
6.
Yu.A. Fridman D.V. Spirin 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):311-313
The quantum spherical XY model with orthorhombic anisotropy is investigated. It is shown that in contradiction with the results
of reference [#!9!#], the long-range magnetic order is stabilized in two dimensions. Both analytical and numerical results
are presented. The incorrect results of the work [9] are explained to be the result of improper choice of quantization axis.
Received 26 August 2002 / Received in final form 24 October 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: frid@tnu.crimea.ua 相似文献
7.
M. Abou Ghantous A. Khater 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):335-341
We present the solution of the full magnetic problem arising from the absence of magnetic translation symmetry in two dimensions
due to an extended magnetic surface step on the surface boundary of an insulating magnetic substrate. The calculation concerns
in particular the spin fluctuation dynamics of a magnetic atomic step in the surface of a ferromagnetic simple cubic lattice,
the spin order being in the direction normal to surface boundary. Only exchange interactions are considered between the spins
in the model. The theoretical approach determines the evanescent spin fluctuation field in the two dimensional plane normal
to the direction of the step edge. This field arises owing to the absence of magnetic translation symmetry in this plane,
and is completely independent of the form of the surface defect, underlying the general character of the calculation. We show
the existence of optical localised magnon modes propagating along the step, their fields being evanescent in the plane normal
to the step direction.
Received 17 February 1999 相似文献
8.
Yu.L. Sokolov V.P. Yakovlev V.G. Pal'chikov Yu.A. Pchelin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):27-36
The properties of two-dimensional magnetic traps for laser-cooled atoms are analysed using complex functions. The two components
of the magnetic field from a series of parallel, infinitely long, current-carrying wires are represented by a single complex
number. The regions of the field where paramagnetic atoms can be trapped occur where the magnetic field is zero. The locations
of the zeroes of the field are obtained as the solution to a polynomial and the multiplicity m of the solution determines both the 2(m + 1)-pole nature of the trap and the field gradient through the centre. The zeroes of the field can be merged or split by
varying the locations of the currents, their strengths or by applying a uniform magnetic field. The theory is applied to magnetic
traps created from long thin wires or permanent magnets on a substrate. The properties of a number of magnetic trap configurations
used for atom guides are discussed.
Received 28 February 2001 and Received in final form 6 July 2001 相似文献
9.
H. Frahm C. Rödenbeck 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):409-414
We study the phase diagram of coupled spin-1/2 chains with bilinear and (chiral) three-spin exchange interactions in a magnetic
field. The model is soluble on a one-parametric line in the space of coupling constants connecting the limiting cases of a
single and two decoupled Heisenberg chains with nearest neighbour exchange only. We give a complete classification of the
low-energy properties of the integrable system and introduce a numerical method which allows to study the possible phases
of spin ladder systems away from the soluble line in a magnetic field.
Received 17 November 1998 and Received in final form 22
January 1999 相似文献
10.
N. El Khayati R. Cherkaoui El Moursli J. Rodríguez-Carvajal G. André N. Blanchard F. Bourée G. Collin T. Roisnel 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):429-442
We have studied in detail the crystal and magnetic structures of the oxyphosphates MFePO5 (M: divalent transition metal) using neutron powder diffraction as a function of temperature. All of them are isomorphic
to the mixed valence compound α-Fe2PO5 with space-group Pnma. No disorder exists between the two metallic sites. The M2+O6 octahedra share edges between them and faces with Fe3+O6 octahedra building zigzag chains running parallel to the b-axis that are connected by PO4 tetrahedra. The topology of this structure gives rise to a complex pattern of super-exchange interactions responsible of
the observed antiferromagnetic order. The magnetic structures are all collinear with the spin directed along the b-axis except for M = Co. The experimental magnetic moments of Cu+2 and Ni2+ correspond to the expected ionic value, on the contrary the magnetic moment of Fe3+ is reduced, probably due to covalence effects, and that of Co2+ is greater than the spin-only value indicating a non negligible orbital contribution. Using numerical calculations we have
established a magnetic phase diagram adapted for this type of crystal structure and determined the constraints to be satisfied
by the values of the exchange interactions in order to obtain the observed magnetic structure as the ground state.
Received 15 December 2000 and Received in final form 25 June 2001 相似文献
11.
M. Labrune A. Thiaville 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(1):17-28
Micromagnetic simulations have been performed in order to obtain deeper insight into the domain structures within multilayer
films, as they are expected to differ from those of single films. These 2D calculations have been done in the case of multilayers
exhibiting a moderate perpendicular anisotropy, with no indirect exchange coupling between the magnetic layers, where a “weak
stripe" domain structure develops. First, these results are compared quantitatively to the very detailed experimental data
available in the literature on the (Co/Au)N system. More generally, the nucleation of a stripe pattern in multilayers is discussed as a function of the magnetic parameters
and the number of magnetic layers in the stack. Compared to a single film, two main differences appear in the equilibrium
domain period and the magnetization profiles. The physical origin of these effects is discussed.
Received 12 January 2001 and Received in final form 15 May 2001 相似文献
12.
C. Tiusan M. Hehn K. Ounadjela 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):431-434
Magnetostatic ferromagnetic coupling in magnetic tunnel junctions was selectively analyzed. We have shown that in samples
involving polycrystalline magnetic films, beyond the orange-peel coupling, an important class of interaction is related to
the dispersion fields associated to magnetic inhomogeneities. These magnetization fluctuations were described in terms of
magnetic roughness arising from the local anisotropy fluctuations. Therefore, using roughness data extracted from atomic/
magnetic force microscopy analysis, the amplitude and the variation with distance of the magnetostatic interactions were selectively
quantified.
Received 7 December 2001 相似文献
13.
Ll. Serra A. Puente 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):77-81
The magnetic extension of the Thomas-Fermi-Weizs?cker kinetic energy is used within density-functional-theory to numerically
obtain the ground state densities and energies of two-dimensional quantum dots. The results are thoroughly compared with the
microscopic Kohn-Sham ones in order to assess the validity of the semiclassical method. Circular as well as deformed systems
are considered.
Received 26 October 2000 and Received in final form 14 December 2000 相似文献
14.
W. Selke V.L. Pokrovsky B. Büchner T. Kroll 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):83-92
Motivated by recent experiments on cuprates with low-dimensional magnetic interactions, a new class of two-dimensional Ising
models with short-range interactions and mobile defects is introduced and studied. The non-magnetic defects form lines, which,
as temperature increases, first meander and then become unstable. Using Monte Carlo simulations and analytical low- and high-temperature
considerations, the instability of the defect stripes is monitored for various microscopic and thermodynamic quantities in
detail for a minimal model, assuming some of the couplings to be indefinitely strong. The robustness of the findings against
weakening the interactions is discussed as well.
Received 22 August 2002 / Received in final form 4 October 2002 Published online 19 November 2002 相似文献
15.
F. Semadeni A. Amato B. Roessli P. Böni C. Baines T. Masuda K. Uchinokura G. Shirane 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):307-311
The temperature-concentration phase diagram of the Si-doped spin-Peierls compound CuGeO3 is investigated by means of neutron scattering and muon spin rotation spectroscopy in order to determine the microscopic
distribution of the magnetic and lattice dimerised regions as a function of doping. The analysis of the zero-field muon spectra
has confirmed the spatial inhomogeneity of the staggered magnetisation that characterises the antiferromagnetic superlattice
peaks observed with neutrons. In addition, the variation of the macroscopic order parameter with doping can be understood
by considering the evolution of the local magnetic moment as well as of the various regions contributing to the muon signal.
Received 6 September 2000 and Received in final form 29 January 2001 相似文献
16.
17.
L. Pareti M. Solzi F. Albertini A. Paoluzi 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):303-307
We have studied the isothermal entropy change around a first-order structural transformation and in correspondence to the
second-order Curie transition in the ferromagnetic Heusler alloy Ni2.15Mn0.85Ga. The results have been compared with those obtained for the composition Ni2.19Mn0.81Ga, in which the martensitic structural transformation and the magnetic transition occur simultaneously. With a magnetic field
span from 0 to 1.6 T, the magnetic entropy change reaches the value of 20 J/kg K when transitions are co-occurring, while
5 J/kg K is found when the only structural transition occurs.
Received 27 September 2002 / Received in final form 17 February 2003 Published online 11 April 2003
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ID="a"e-mail: solzi@fis.unipr.it 相似文献
18.
A.A. Zvyagin A. Klümper J. Zittartz 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):25-36
The exactly solvable model of supersymmetric t - J chains (STJC) of correlated electrons with next-nearest-neighbour (NNN) interactions is proposed and studied. The model with
interactions between nearest neighbours and NNN interactions in one chain can also be considered as a two-chain model with
zigzag-like coupling between the chains. The NNN interaction (coupling between chains) causes the onset of additional Dirac
seas for low-lying charge and/or spin excitations. These Dirac seas change the low-energy (conformal) behavior of the model.
The filling of those seas depends on the values of the NNN coupling (interactions between chains), external magnetic field
and applied voltage. We identify the new ground state phases which appear due to the NNN as incommensurate ones. The NNN coupling
in the incommensurate phases induces spontaneous magnetization and/or spontaneous filling of the Dirac sea for charge excitations
(“spontaneous charge ordering”). The onset of this order implies a first order quantum phase transition driven by the field
with hysteresis phenomena.
Received 13 September 2000 相似文献
19.
V. Franco X. Batlle A. Labarta 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(1):43-50
Thin films of the giant magnetoresistive granular CoFe-AgCu system prepared by rf sputtering displayed a great variety of
domain-like microstructures with a net out-of-plane component of the magnetization for ferromagnetic volume concentrations
above about 0.25. Therefore, magnetic percolation takes place at ferromagnetic concentrations much lower than the physical
percolation threshold. The out-of-plane structure of the as-deposited samples in magnetic virgin state consisted of a distribution
of both quasi-circular domains and short stripes depending on the ferromagnetic content. Furthermore, these samples present
high metastability and a variety of remanent in-plane and out-of-plane microstructures can be achieved as a function of the
magnetic history. Besides, the evolution of the magnetic microstructure yields strong training effects on magnetotransport
properties, due to the extra contribution of the electron scattering at the domain walls. All in all, the observed behavior
is the result of a subtle correlation between perpendicular anisotropy produced by residual stresses, exchange interparticle
interactions due to CoFe alloyed in the matrix, and dipolar interactions. Thus, as high structural evolution occurs through
annealing, the features of randomly distributed ferromagnetic particles are recovered and, the out-of-plane domain structures
and the training effects disappear.
Received 30 September 1999 相似文献
20.
M.A. Continentino J.C. Fernandes R.B. Guimar aes H.A. Borges A. Sulpice J.-L. Tholence J.L. Siqueira J.B.M. da Cunha C.A. dos Santos 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):613-618
The system Cu2FeO2BO3 is an oxyborate belonging to the family of the ludwigites. In this paper we present AC susceptibility, magnetization measurements
and M?ssbauer spectroscopy on this material which allows for a complete characterization of its complex magnetic behavior.
We find an hierarchy of interactions which clearly defines three regimes with decreasing temperature. These are associated
with, the freezing of the Fe moments, the antiferromagnetic ordering of the Cu sub-lattice and finally the coupling between
both systems.
Received 25 September 1998 相似文献