373 research outputs found
Kinetic Ising model in an oscillating field: Finite-size scaling at the dynamic phase transition
We study hysteresis for a two-dimensional, spin-1/2, nearest-neighbor,
kinetic Ising ferromagnet in an oscillating field, using Monte Carlo
simulations. The period-averaged magnetization is the order parameter for a
proposed dynamic phase transition (DPT). To quantify the nature of this
transition, we present the first finite-size scaling study of the DPT for this
model. Evidence of a diverging correlation length is given, and we provide
estimates of the transition frequency and the critical indices ,
and .Comment: Accepted by Physical Review Letters. 9 page
Kinetic Ising System in an Oscillating External Field: Stochastic Resonance and Residence-Time Distributions
Experimental, analytical, and numerical results suggest that the mechanism by
which a uniaxial single-domain ferromagnet switches after sudden field reversal
depends on the field magnitude and the system size. Here we report new results
on how these distinct decay mechanisms influence hysteresis in a
two-dimensional nearest-neighbor kinetic Ising model. We present theoretical
predictions supported by numerical simulations for the frequency dependence of
the probability distributions for the hysteresis-loop area and the
period-averaged magnetization, and for the residence-time distributions. The
latter suggest evidence of stochastic resonance for small systems in moderately
weak oscillating fields.Comment: Includes updated results for Fig.2 and minor text revisions to the
abstract and text for clarit
Nonequilibrium phase transition in the kinetic Ising model: Is transition point the maximum lossy point ?
The nonequilibrium dynamic phase transition, in the kinetic Ising model in
presence of an oscillating magnetic field, has been studied both by Monte Carlo
simulation (in two dimension) and by solving the meanfield dynamical equation
of motion for the average magnetization. The temperature variations of
hysteretic loss (loop area) and the dynamic correlation have been studied near
the transition point. The transition point has been identified as the
minimum-correlation point. The hysteretic loss becomes maximum above the
transition point. An analytical formulation has been developed to analyse the
simulation results. A general relationship among hysteresis loop area, dynamic
order parameter and dynamic correlation has also been developed.Comment: 8 pages Revtex and 4 Postscript figures; To appear in Phys. Rev.
Spatial stochastic resonance in 1D Ising systems
The 1D Ising model is analytically studied in a spatially periodic and
oscillatory external magnetic field using the transfer-matrix method. For low
enough magnetic field intensities the correlation between the external magnetic
field and the response in magnetization presents a maximum for a given
temperature. The phenomenon can be interpreted as a resonance phenomenon
induced by the stochastic heatbath. This novel "spatial stochastic resonance"
has a different origin from the classical stochastic resonance phenomenon.Comment: REVTex, 5 pages, 3 figure
Hysteresis and the dynamic phase transition in thin ferromagnetic films
Hysteresis and the non-equilibrium dynamic phase transition in thin magnetic
films subject to an oscillatory external field have been studied by Monte Carlo
simulation. The model under investigation is a classical Heisenberg spin system
with a bilinear exchange anisotropy in a planar thin film geometry with
competing surface fields. The film exhibits a non-equilibrium phase transition
between dynamically ordered and dynamically disordered phases characterized by
a critical temperature Tcd, whose location of is determined by the amplitude H0
and frequency w of the applied oscillatory field. In the presence of competing
surface fields the critical temperature of the ferromagnetic-paramagnetic
transition for the film is suppressed from the bulk system value, Tc, to the
interface localization-delocalization temperature Tci. The simulations show
that in general Tcd < Tci for the model film. The profile of the time-dependent
layer magnetization across the film shows that the dynamically ordered and
dynamically disordered phases coexist within the film for T < Tcd. In the
presence of competing surface fields, the dynamically ordered phase is
localized at one surface of the film.Comment: PDF file, 21 pages including 8 figure pages; added references,typos
added; to be published in PR
Magnetic Behavior of a Mixed Ising Ferrimagnetic Model in an Oscillating Magnetic Field
The magnetic behavior of a mixed Ising ferrimagnetic system on a square
lattice, in which the two interpenetrating square sublattices have spins +- 1/2
and spins +-1,0, in the presence of an oscillating magnetic field has been
studied with Monte Carlo techniques. The model includes nearest and
next-nearest neighbor interactions, a crystal field and the oscillating
external field. By studying the hysteretic response of this model to an
oscillating field we found that it qualitatively reproduces the increasing of
the coercive field at the compensation temperature observed in real
ferrimagnets, a crucial feature for magneto-optical applications. This behavior
is basically independent of the frequency of the field and the size of the
system. The magnetic response of the system is related to a dynamical
transition from a paramagnetic to a ferromagnetic phase and to the different
temperature dependence of the relaxation times of both sublattices.Comment: 10 figures. To be published in Phys.Rev
Entropic sampling dynamics of the globally-coupled kinetic Ising model
The entropic sampling dynamics based on the reversible information transfer
to and from the environment is applied to the globally coupled Ising model in
the presence of an oscillating magnetic field. When the driving frequency is
low enough, coherence between the magnetization and the external magnetic field
is observed; such behavior tends to weaken with the system size. The time-scale
matching between the intrinsic time scale, defined in the absence of the
external magnetic field, and the extrinsic time scale, given by the inverse of
the driving frequency, is used to explain the observed coherence behavior.Comment: 8 page
Dynamic Phase Transition, Universality, and Finite-size Scaling in the Two-dimensional Kinetic Ising Model in an Oscillating Field
We study the two-dimensional kinetic Ising model below its equilibrium
critical temperature, subject to a square-wave oscillating external field. We
focus on the multi-droplet regime where the metastable phase decays through
nucleation and growth of many droplets of the stable phase. At a critical
frequency, the system undergoes a genuine non-equilibrium phase transition, in
which the symmetry-broken phase corresponds to an asymmetric stationary limit
cycle for the time-dependent magnetization. We investigate the universal
aspects of this dynamic phase transition at various temperatures and field
amplitudes via large-scale Monte Carlo simulations, employing finite-size
scaling techniques adopted from equilibrium critical phenomena. The critical
exponents, the fixed-point value of the fourth-order cumulant, and the critical
order-parameter distribution all are consistent with the universality class of
the two-dimensional equilibrium Ising model. We also study the cross-over from
the multi-droplet to the strong-field regime, where the transition disappears
Stationary Properties of a Randomly Driven Ising Ferromagnet
We consider the behavior of an Ising ferromagnet obeying the Glauber dynamics
under the influence of a fast switching, random external field. Analytic
results for the stationary state are presented in mean-field approximation,
exhibiting a novel type of first order phase transition related to dynamic
freezing. Monte Carlo simulations performed on a quadratic lattice indicate
that many features of the mean field theory may survive the presence of
fluctuations.Comment: 5 pages in RevTex format, 7 eps/ps figures, send comments to
"mailto:[email protected]", submitted to PR
Microscopic elasticity of complex systems
Lecture Notes for the Erice Summer School 2005 Computer Simulations in
Condensed Matter: from Materials to Chemical Biology. Perspectives in
celebration of the 65th Birthday of Mike Klein organized by Kurt Binder,
Giovanni Ciccotti and Mauro Ferrari
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