Dynamic phase transition features of the cylindrical nanowire driven by a propagating magnetic field

Magnetic response of the spin-$1/2$ 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 $\sigma=1/2$ and the shell contains Ising spins of $S=1$. 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 ($q=6$) 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