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We used the Curie–Weiss mean-field approximation to study the effects of random single-ion anisotropy and random magnetic field in the phase diagram as well as in the thermodynamic properties of the spin-7/2 Blume–Capel model. The phase diagrams are presented in the planes temperature versus single-ion anisotropy and temperature versus magnetic field, temperature versus random parameters. The dependencies of magnetization are studied as a function of temperature and single-ion anisotropy. • Phase diagrams of the system with a random anisotropies and random field were obtained. • To investigate the system, Curie–Weiss mean-field approximation were used. • First- and second-order phase transition lines for different anisotropies were found. • Tricritical behavior for some values of anisotropy and magnetic field were observed. [ABSTRACT FROM AUTHOR]

In this work, we have performed Monte Carlo simulations to study a mixed spin-1 and spin-3/2 Ising ferrimagnetic system on a square lattice with two different random single-ion anisotropies. This lattice is divided in two interpenetrating sublattices with spins S A = 1 in the sublattice A and S B = 3 ∕ 2 in the sublattice B . The exchange interaction between the spins on the sublattices is antiferromagnetic ( J < 0 ). We used two random single-ion anisotropies, D i A and D j B , on the sublattices A and B , respectively. We have determined the phase diagram of the model in the critical temperature T c versus strength of the random single-ion anisotropy D plane and we shown that it exhibits only second-order phase transition lines. We also shown that this system displays compensation temperatures for some cases of the random single-ion distribution. [ABSTRACT FROM AUTHOR]

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]

Abstract We have studied the effects of the random transverse single-ion anisotropy in the phase diagram and in the thermodynamic properties of the spin − 1 Blume–Capel quantum model, which has been used the approach the mean-field theory based on the Bogoliubov inequality for the Gibbs free energy. The phase diagrams were obtained in the temperature τ = k B T ∕ z J versus single-ion anisotropy δ x = D x ∕ z J plane for several values of δ y = D y ∕ z J , p and q. The results show that there is a tricritical behavior only in the range of δ y given by − 0. 048 ≤ δ y < 0. 5. This behavior is shown again by the curves of the magnetization m as a function of temperature τ with corresponding values of δ y , p and q. Highlights • Several phase diagrams were obtained for the spin-1 Blume–Capel quantum model. • The influence of the random single-ion anisotropies was examined for the system. • First- and second-order phase transition lines were found. • The tricritical behavior was examined. [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]