Dynamic dipole and quadrupole phase transitions in the kinetic spin-1 model

The dynamic phase transitions have been studied, within a mean-field approach, in the kinetic spin-1 Ising model Hamiltonian with arbitrary bilinear and biquadratic pair interactions in the presence of a time varying (sinusoidal) magnetic field by using the Glauber-type stochastic dynamics. The nature (first- or second-order) of the transition is characterized by investigating the behavior of the thermal variation of the dynamic order parameters. The dynamic phase transitions (DPTs) are obtained and the phase diagrams are constructed in the temperature and magnetic field amplitude plane and found six fundamental types of phase diagrams. Phase diagrams exhibit one or two dynamic tricritical points depending on the biquadratic interaction (K). Besides the disordered (D) and ferromagnetic (F) phases, the FQ + D, F + FQ and F + D coexistence phase regions also exist in the system and the F and F + D phases disappear for high values of K.Comment: 13 pages, 4 figure

Kinetics of a mixed spin-1/2 and spin-3/2 Ising ferrimagnetic model

We present a study, within a mean-field approach, of the kinetics of a mixed ferrimagnetic model on a square lattice in which two interpenetrating square sublattices have spins that can take two values, $\sigma=\pm1/2$, alternated with spins that can take the four values, $S=\pm3/2, \pm1/2$. We use the Glauber-type stochastic dynamics to describe the time evolution of the system with a crystal-field interaction in the presence of a time-dependent oscillating external magnetic field. The nature (continuous and discontinuous) of transition is characterized by studying the thermal behaviors of average order parameters in a period. The dynamic phase transition points are obtained and the phase diagrams are presented in the reduced magnetic field amplitude $(h)$ and reduced temperature $(T)$ plane, and in the reduced temperature and interaction parameter planes, namely in the $(h, T)$ and $(d, T)$ planes, $d$ is the reduced crystal-field interaction. The phase diagrams always exhibit a tricritical point in $(h, T)$ plane, but do not exhibit in the $(d, T)$ plane for low values of $h$. The dynamic multicritical point or dynamic critical end point exist in the $(d, T)$ plane for low values of $h$. Moreover, phase diagrams contain paramagnetic $(p)$, ferromagnetic $(f)$, ferrimagnetic $(i)$ phases, two coexistence or mixed phase regions, $(f+p)$ and $(i+p)$, that strongly depend on interaction parameters.Comment: 13 pages, 6 figures, submitted to Journal of Magnetism and Magnetic Material

The ground-state phase diagrams of the spin-3/2 Ising model

The ground-state spin configurations are obtained for the spin-3/2 Ising model Hamiltonian with bilinear and biquadratic exchange interactions and a single-ion crystal field. The interactions are assumed to be only between nearest-neighbors. The calculated ground-state phase diagrams are presented on diatomic lattices, such as the square, honeycomb and sc lattices, and triangular lattice in the (Delta/z\J\, K/\J\) and (H/z\J\, K/\J\) planes. (C) 2003 Published by Elsevier B.V

Time dependence of the weakly coupled spin-1 Ising system using the Glauber model

We study the time dependence of the one-dimensional weakly coupled spin-l Ising system by means of the modified version of Glauber's one-dimensional spin relaxation model and the system of dynamic equations for the one- and two-points functions is derived. We solve the dynamic equations analytically and find the exact solutions for the relaxation times in the weak coupling limit. We also make a comparison with the relaxation times which were found by a first-order perturbation method. (C) 2002 Elsevier Science B.V. All rights reserved

Relaxation theory of spin-3/2 Ising system near phase transition temperatures

Dynamics of a spin-3/2 Ising system Hamiltonian with bilinear and biquadratic nearest-neighbour exchange interactions is studied by a simple method in which the statistical equilibrium theory is combined with the Onsager's theory of irreversible thermodynamics. First, the equilibrium behaviour of the model in the molecular-field approximation is given briefly in order to obtain the phase transition temperatures, i.e. the first- and second-order and the tricritical points. Then, the Onsager theory is applied to the model and the kinetic or rate equations are obtained. By solving these equations three relaxation times are calculated and their behaviours are examined for temperatures near the phase transition points. Moreover, the z dynamic critical exponent is calculated and compared with the z values obtained for different systems experimentally and theoretically, and they are found to be in good agrement