106 research outputs found
Dynamic phase transition features of the cylindrical nanowire driven by a propagating magnetic field
Magnetic response of the spin- cylindrical nanowire to the propagating
magnetic field wave has been investigated by means of Monte Carlo simulation
method based on Metropolis algorithm. The obtained microscopic spin
configurations suggest that the studied system exhibits two types of dynamical
phases depending on the considered values of system parameters: Coherent
propagation of spin bands and spin-frozen or pinned phases, as in the case of
the conventional bulk systems under the influence of a propagating magnetic
field. By benefiting from the temperature dependencies of variances of dynamic
order parameter, internal energy and the derivative of dynamic order parameter
of the system, dynamic phase diagrams are also obtained in related planes for
varying values of the wavelength of the propagating magnetic field. Our
simulation results demonstrate that as the strength of the field amplitude is
increased, the phase transition points tend to shift to the relatively lower
temperature regions. Moreover, it has been observed that dynamic phase boundary
line shrinks inward when the value of wavelength of the external field
decreases.Comment: 7 pages, 4 figure
Dynamic phase transitions in a ferromagnetic thin film system: A Monte Carlo simulation study
Dynamic phase transition properties of ferromagnetic thin film system under
the influence both bias and time dependent magnetic fields have been elucidated
by means of kinetic Monte Carlo simulation with local spin update Metropolis
algorithm. The obtained results after a detailed analysis suggest that bias
field is the conjugate field to dynamic order parameter, and it also appears to
define a phase line between two antiparallel dynamic ordered states depending
on the considered system parameters. Moreover, the data presented in this study
well qualitatively reproduce the recently published experimental findings where
time dependent magnetic behavior of a uniaxial cobalt films is studied in the
neighborhood of dynamic phase transition point.Comment: 15 pages, 5 Figure
Nonequilibrium dynamics of a mixed spin-1/2 and spin-3/2 Ising ferrimagnetic system with a time dependent oscillating magnetic field source
Nonequilibrium phase transition properties of a mixed Ising ferrimagnetic
model consisting of spin-1/2 and spin-3/2 on a square lattice under the
existence of a time dependent oscillating magnetic field have been investigated
by making use of Monte Carlo simulations with single-spin flip Metropolis
algorithm. A complete picture of dynamic phase boundary and magnetization
profiles have been illustrated and the conditions of a dynamic compensation
behavior have been discussed in detail. According to our simulation results,
the considered system does not point out a dynamic compensation behavior, when
it only includes the nearest-neighbor interaction, single-ion anisotropy and an
oscillating magnetic field source. As the next-nearest-neighbor interaction
between the spins-1/2 takes into account and exceeds a characteristic value
which sensitively depends upon values of single-ion anisotropy and only of
amplitude of external magnetic field, a dynamic compensation behavior occurs in
the system. Finally, it is reported that it has not been found any evidence of
dynamically first-order phase transition between dynamically ordered and
disordered phases, which conflicts with the recently published molecular field
investigation, for a wide range of selected system parameters.Comment: 10 pages, 7 figure
Nonequilibrium dynamics of a spin-3/2 Blume Capel model with quenched random crystal field
The relaxation and complex magnetic susceptibility treatments of a spin-3/2
Blume-Capel model with quenched random crystal field on a two dimensional
square lattice are investigated by a method combining the statistical
equilibrium theory and the thermodynamics of linear irreversible processes.
Generalized force and flux are defined in irreversible thermodynamics limit.
The kinetic equation for the magnetization is obtained by using linear response
theory. Temperature and also crystal field dependencies of the relaxation time
are obtained in the vicinity of phase transition points. We found that the
relaxation time exhibits divergent treatment near the order-disorder phase
transition point as well as near the isolated critical point whereas it
displays cusp behavior near the first order phase transition point. In
addition, much effort has been devoted to investigation of complex magnetic
susceptibility response of the system to changing applied field frequencies and
it is observed that the considered disordered magnetic system exhibits unusual
and interesting behaviors. Furthermore, dynamical mean field critical exponents
for the relaxation time and complex magnetic susceptibility are calculated in
order to formulate the critical behavior of the system. Finally, a comparison
of our observations with those of recently published studies is represented and
it is shown that there exists a qualitatively good agreement.Comment: 13 pages, 8 figure
Nonequilibrium Multiple Transitions in the Core-shell Ising Nanoparticles Driven by Randomly Varying Magnetic Fields
The nonequilibrium behaviour of a core-shell nanoparticle has been studied by
Monte- Carlo simulation. The core consists of Ising spins of and
the shell contains Ising spins of . The interactions within the core and
in the shell are considered ferromagnetic but the interfacial interaction
between core and shell is antiferromagnetic. The nanoparticle system is kept in
open boundary conditions and is driven by randomly varying (in time but uniform
over the space) magnetic field. Depending on the width of the randomly varying
field and the temperature of the system, the core, shell and total
magnetization varies in such a manner that the time averages vanish for higher
magnitude of the width of random field, exhibiting a dynamical symmetry
breaking transitions. The susceptibilities get peaked at two different
temperatures indicating nonequilibrium multiple transitions. The phase
boundaries of the nonequilibrium multiple transitions are drawn in the plane
formed by the axes of temperature and the width of the randomly varying field.
Furthermore, the effects of the core and shell thicknesses on the multiple
transitions have been discussed.Comment: 14 pages Latex including 8 captioned figure
Monte Carlo study of the two-dimensional kinetic Blume-Capel model in a quenched random crystal field
We investigate by means of Monte Carlo simulations the dynamic phase
transition of the two-dimensional kinetic Blume-Capel model under a
periodically oscillating magnetic field in the presence of a quenched random
crystal-field coupling. We analyze the universality principles of this dynamic
transition for various values of the crystal-field coupling at the originally
second-order regime of the corresponding equilibrium phase diagram of the
model. A detailed finite-size scaling analysis indicates that the observed
nonequilibrium phase transition belongs to the universality class of the
equilibrium Ising ferromagnet with additional logarithmic corrections in the
scaling behavior of the heat capacity. Our results are in agreement with
earlier works on kinetic Ising models.Comment: 25 pages (APS preprint style), 13 figures, 1 tabl
Ising universality in the two-dimensional Blume-Capel model with quenched random crystal field
Using high-precision Monte-Carlo simulations based on a parallel version of
the Wang-Landau algorithm and finite-size scaling techniques we study the
effect of quenched disorder in the crystal-field coupling of the Blume-Capel
model on the square lattice. We mainly focus on the part of the phase diagram
where the pure model undergoes a continuous transition, known to fall into the
universality class of the pure Ising ferromagnet. A dedicated scaling analysis
reveals concrete evidence in favor of the strong universality hypothesis with
the presence of additional logarithmic corrections in the scaling of the
specific heat. Our results are in agreement with an early real-space
renormalization-group study of the model as well as a very recent numerical
work where quenched randomness was introduced in the energy exchange coupling.
Finally, by properly fine tuning the control parameters of the randomness
distribution we also qualitatively investigate the part of the phase diagram
where the pure model undergoes a first-order phase transition. For this region,
preliminary evidence indicate a smoothening of the transition to second-order
with the presence of strong scaling corrections.Comment: 11 pages, 13 figures, minor correction to references appearing in
Fig. 1, to be published in Phys. Rev.
Nonequilibrium phase transitions and stationary state solutions of a three-dimensional random-field Ising model under a time dependent periodic external field
Nonequilibrium behavior and dynamic phase transition properties of a kinetic
Ising model under the influence of periodically oscillating random-fields have
been analyzed within the framework of effective field theory (EFT) based on a
decoupling approximation (DA). Dynamic equation of motion has been solved for a
simple cubic lattice () by utilizing a Glauber type stochastic process.
Amplitude of the sinusoidally oscillating magnetic field is randomly
distributed on the lattice sites according to bimodal and trimodal distribution
functions. For a bimodal type of amplitude distribution, it is found in the
high frequency regime that the dynamic phase diagrams of the system in
temperature versus field amplitude plane resemble the corresponding phase
diagrams of pure kinetic Ising model. Our numerical results indicate that for a
bimodal distribution, both in the low and high frequency regimes, the dynamic
phase diagrams always exhibit a coexistence region in which the stationary
state (ferro or para) of the system is completely dependent on the initial
conditions whereas for a trimodal distribution, coexistence region disappears
depending on the values of system parameters.Comment: 11 pages, 11 figure
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