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Abstract: We study the effect of two different single-ion anisotropies in the phase diagram and in the compensation temperature of mixed spin-2 and spin- Ising ferrimagnetic system. We employed the mean-field theory based on the Bogoliubov inequality for Gibbs free energy. We use the Landau expansion of free energy in the order parameter to describe the phase diagram. In the temperature versus single-ion anisotropy plane the phase diagram displays tricritical behavior. The critical and compensation temperatures increase with increasing values of the single-ion anisotropies. [Copyright &y& Elsevier]

Abstract: The phase diagram of an Ising metamagnet in a random magnetic field is studied by using mean-field equations from Bogoliubov''s variational principle. The trimodal probability distribution is applied. The phase diagram in the plane presents continuous and first-order transition lines. The phase transition lines, together with the critical points, were obtained for several random field values. [Copyright &y& Elsevier]

We study the mixed spin-1 and spin-3/2 ferrimagnetic Ising system under the effect of different random crystal-fields within the mean-field theory based on the Bogoliubov inequality for the Gibbs free energy. The phase diagrams are obtained in the plane of critical temperature versus random crystal-field, showing a tricritical behavior with second-order transition lines separating the first-order transition lines by tricritical points. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we used the Cluster Wolff algorithms to simulate the dynamics of the system. We obtained the thermodynamic quantities such as magnetization and susceptibility. Critical temperatures were estimated at the maximum of the susceptibility and with these values we made the phase diagram, versus (the concentration of magnetic bonds) for different values, being the competition parameter. Our results were compared to those obtained by using a new technique in the effective field theory which employs similar probability distribution within the framework of two-site clusters. [Copyright &y& Elsevier]