It has been well established that the spin-1 Blume–Capel (BC) model in a time-dependent oscillating external field and a crystal field interaction exhibits a rich variety of topology in nonequilibrium dynamic phase diagrams. Some interesting dynamic behaviors, quite different from the standard Ising model, have been observed. However, there are some disagreements among these theoretical studies. Here we use the effective-field theory (EFT) and the Monte Carlo method (MC) to show that the dissimilarity among the mean-field theory and EFT results is due to the neglect of thermal fluctuations. The effects of thermal fluctuations on the dynamic phase boundary and the dynamic tricritical point are investigated. The MC method is then carried out to confirm if the reentrant phenomenon obtained by the EFT is correct or not. The dynamic phase diagram of the kinetic BC model given by the MC method is also plotted.
It has been well established that the spin-1 Blume–Capel (BC) model in a time-dependent oscillating external field and a crystal field interaction exhibits a rich variety of topology in nonequilibrium dynamic phase diagrams. Some interesting dynamic behaviors, quite different from the standard Ising model, have been observed. However, there are some disagreements among these theoretical studies. Here we use the effective-field theory (EFT) and the Monte Carlo method (MC) to show that the dissimilarity among the mean-field theory and EFT results is due to the neglect of thermal fluctuations. The effects of thermal fluctuations on the dynamic phase boundary and the dynamic tricritical point are investigated. The MC method is then carried out to confirm if the reentrant phenomenon obtained by the EFT is correct or not. The dynamic phase diagram of the kinetic BC model given by the MC method is also plotted.
The dynamic magnetic behavior of the kinetic metamagnetic spin-5/2 Blume—Capel model is examined, within a mean-field approach, under a time-dependent oscillating magnetic field. To describe the kinetics of the system, Glauber-type stochastic dynamics has been utilized. The mean-field dynamic equations of the model are obtained from the Master equation. Firstly, these dynamic equations are solved to find the phases in the system. Then, the dynamic phase transition temperatures are obtained by investigating the thermal behavior of dynamic sublattice magnetizations. Moreover, from this investigation, the nature of the phase transitions (first- or second-order) is characterized. Finally, the dynamic phase diagrams are plotted in five different planes. It is found that the dynamic phase diagrams contain the paramagnetic (P), antiferromagnetic (AF 5/2 , AF 3/2 , AF 1/2 ) phases and five different mixed phases. The phase diagrams also display many dynamic critical points, such as tricritical point, triple point, quadruple point, double critical end point and separating point.
Within a mean-field approach, the stationary states of the kinetic spin-1 Blume-Capel model in the presence of a time-dependent oscillating external magnetic field is studied. The Glauber-type stochastic dynamics is used to describe the time evolution of the system and obtain the mean-field dynamic equation of motion. The dynamic phase-transition points are calculated and phase diagrams are presented in the temperature and crystal-field interaction plane. According to the values of the magnetic field amplitude, three fundamental types of phase diagrams are found: One exhibits a dynamic tricritical point, while the other two exhibit a dynamic zero-temperature critical point.
The Jx-Jy Blume-Capel model, with and without an external magnetic field, is investigated using the Monte Carlo method. Our aim is to verify the location of the tricritical point, examine the existence of reentrant behavior, and study the magnetocaloric properties of this specifically designed system. In the non-field case, the critical temperature given by the Monte Carlo simulations is lower compared to the conventional antiferromagnetic square lattice. When an external magnetic field is applied, we observed signs of a one-dimensional spontaneous symmetry-breaking phase in the mixed-states regime, which is counterintuitive with secondary specific-heat peak. We take the snapshot of this state and elucidated the underlying mechanisms using mean field theory in the field of spin-1 spinor Bose-Einstein condensate . Regarding reentrant behavior, we confirmed its occurrence as the magnetic field varies, but only when the temperature is kept constant. Temperature-dependent reentrant behavior could not be identified within this system. Finally, we examined the magnetocaloric properties and found no evidence of first-order phase transitions within the region of the considered phase-transition point. Although both inverse and direct magnetocaloric effects are present and related to the mixed state, we identified that the relevant phase transitions are all of the second order.
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.
The dynamical phase transitions of the kinetic Ising model in the presence of a random magnetic field with a bimodal probability distribution is studied by using effective-field theory (EFT) with correlations. We have used a Glauber-type stochastic dynamic to describe the time evolution of the system, where the system strongly depends on the H≡√<H(i)(2)>(c) root mean square deviation of the magnetic field. The EFT dynamic equation is given for the simple cubic lattice (z=6), and the dynamic order parameter is calculated. The system presents ferromagnetic and paramagnetic states for low and high temperatures, respectively. Our results predict first-order transitions at low temperatures and large disorder strengths, which corresponds to the existence of a nonequilibrium tricritical point (TCP) in a phase diagram in the T-H plane. We compare the results with the equilibrium phase diagram, where only the first-order line is different. Our qualitative results are compatible with recent Monte Carlo simulations.