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We have used the Curie–Weiss mean-field approximation to study the effects of the random single-ion anisotropy and random magnetic field in the phase diagram and thermodynamic properties of the spin-5/2 Blume–Capel model. The phase diagrams have been presented in the temperature T ∕ J versus strength random single-ion anisotropy D ∕ J and strength random magnetic field h ∕ J planes. The magnetization dependence was plotted as a function of temperature and the strength single-ion anisotropy. These diagrams showed that the different phase transition types, first-or second-order between the ferromagnetic and paramagnetic phases, are dependent on the random parameters. Therefore, within these conditions, the model presents tricritical behavior. • Several phase diagrams were obtained for the spin-5/2 Blume–Capel model. • The influence of the random single-ion anisotropy and magnetic field was examined for the system. • First- and second-order phase transition lines were found. • The tricritical behavior was examined. [ABSTRACT FROM AUTHOR]

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]

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]

Purpose: The authors investigate the magnetic properties of a mixed spin-3/2 and spin-2 Blume-Capel model on square and cubic lattices with two different single-ion anisotropies. Design/methodology/approach: To study the critical behavior of a mixed spin-3/2 and spin-2 system, the authors have used a real space renormalization group approximation and specifically the Migdal-Kadanoff technique. The authors give the phase diagrams for two different cases: (1) on the (Δ/|J|, 1/|J|) plane with ΔA = ΔB = Δ, and (2) on the (ΔA/|J|, 1/|J|) and (ΔB/|J|, 1/|J|) planes for selected values of ΔB/|J| and ΔA/|J|, respectively. Findings: The phase diagrams obtained show that the system exhibits both second- and first-order phase transitions as well as tricritical points for some values of the anisotropies. Moreover, using the variation of the free energy and its derivative at low temperatures, the authors have seen the appearance of first-order transitions at very low temperatures. Originality/value: Few investigations of mixed spin-3/2 and spin-2 systems with crystal field have been realized. For this reason, the authors use the renormalization group approach to complete the work done on these systems. In absence of an exact solution, this contributes to the synthesis of the approximation results on mixed spins models. [ABSTRACT FROM AUTHOR]

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]

We have studied the effects of two different random single-ion anisotropies in the phase diagram and on the critical properties of a mixed spin-2 and spin-5/2 Ising ferrimagnetic system. We employed the mean-field theory based on the Bogoliubov inequality for the Gibbs free energy. We have used the Landau expansion of the free energy in the order parameter to describe the phase diagram. We have shown that the phase diagram temperature as function of random single-ion anisotropy displays tricritical behavior. We also investigated the existence and dependence of a compensation temperature on random single-ion anisotropies. The critical and compensation temperatures increase with increasing of the random single-ion anisotropies values. [ABSTRACT FROM AUTHOR]