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We reveal the interplay between on-site ( U ) and intersite ( V ) Coulomb interactions in the extended two-site Hubbard model. Due to its atomic-like form quantum correlations intrinsic to Mott-molecular-dimers are exactly computed. Our results for physical quantities such as double occupancy and specific heat are consistent with those obtained for the one-band Hubbard model, suggesting that a two-site dimer model is able to capture the essential thermodynamic properties of strongly interacting electron systems. It is noted that intersite Coulomb interactions promote the formation of doublons, which compete with the spin-singlet state induced by the on-site Coulomb repulsion. Our results are expected to be relevant for understanding electronic and thermodynamical properties of interacting electrons in systems with strongly coupled magnetic atoms. [ABSTRACT FROM AUTHOR]

In the present work, we will study the effect of dimensionality (i.e 2 + 1 and 3 + 1) has on the different types of coupling in a two-band superconducting system, specifically for the Josephson, bi-quadratic and weak type couplings. This study will be oriented to a ZFC (Zero-Field-Cooling) process and we will see the effect that the variation of temperature for three special cases of the external field (fixed, H < H 1 , H = H 1 and H > H 1) has on the order parameter ψ , phase ψ , magnetization M and free energy G (T) in these superconductors of multibands and a comparison between the behavior of these electronic and thermodynamic variables. This analysis will be carried out using the solution of time-dependent two bands Ginzburg-Landau equations (2B-TDGL). • Dimensionality (2 + 1 and 3 + 1), the type of couplings (Josephson, bi-quadratic and weak), and the temperature of the sample. • Two bands Ginzburg-Landau equations for a two-band system (2B-TDGL). [ABSTRACT FROM AUTHOR]

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]

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]

We have considered a generalized version of a model consisting of self-propelled particles, where the speed is treated as an independent stochastic variable described by a Gamma-distribution, and the motion direction is adjusted in according to two behavioral rules: repulsion and orientation. We used the finite-size scaling theory to estimate the static critical exponents β , γ and ν as a function of the density ρ . We have obtained different values of the critical exponents for different values of the density ρ . [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]

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: By using the differential operator technique and the effective field theory (EFT) scheme, the critical behavior of amorphous classical XY ferromagnet in a random field is studied. The phase diagram in the and planes on a simple cubic lattice for a cluster with two spins is obtained. Calculation is carried out within the EFT approximation. Tricritical points, reentrant phenomena and influence of the random field and amorphization on the transition temperature are discussed. [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]

In this paper we have studied the stabilization of the long-range order in ( z ; x ) -plane of two isotropic Heisenberg ferromagnetic monolayers coupled by a short-range exchange interaction ( J ⊥ ), by a long range dipole-dipole interactions and a magnetic field. We have applied a magnetic field along of the z -direction to study the thermodynamic properties above the critical temperature. The dispersion relation ω and the magnetization are given as function of dipolar anisotropy parameter defined as E d = ( g μ ) 2 S / a 3 J ∥ and for other Hamiltonian parameters, and they are calculated by the double-time Zubarev-Tyablikov Green's functions in the random-phase approximation (RPA). The results show that the system is unstable for values of E d ≥ 0.012 with external magnetic field ranging between H / J ∥ = 0 and 1 0 − 3 . The instability appears for E d larger then E d c = 0.0158 with H / J ∥ = 1 0 − 5 , E d c = 0.02885 with H / J ∥ = 1 0 − 4 , and E d c = 0.115 with H / J ∥ = 1 0 − 3 , i.e., a small magnetic field is sufficient to maintain the magnetic order in a greater range of the dipolar interaction. [ABSTRACT FROM AUTHOR]

We have studied the effects of the random single-ion anisotropy and random magnetic field in the phase diagram and in the thermodynamic properties of the spin-3/2 Blume–Capel model via Curie–Weiss mean-field approximation. The phase diagrams were built in the planes temperature versus single-ion anisotropy, temperature versus magnetic field, temperature versus random parameters and the dependencies of magnetization were plotted versus temperature and single-ion anisotropy. These diagrams show that, in the space ( D / J − T / J ) , the type (first- or second-order) of the phase transition between the ferromagnetic and paramagnetic phases is dependent on the random parameters. Therefore, within these conditions the model presents tricritical behavior. For large values, and a certain critical value of the random parameters, the phase transition is only of second-order, but it is of first-order within the ordered phase, between the phase with m = 1 / 2 and m = 3 / 2 , which ends in a terminal critical point. [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]

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]