We study the phase diagram and multicritical behavior of the semi-infinite quantum spin 1/2 anisotropic Heisenberg and classical O(n) models. We use correlated effective field theory. The multicritical point Δc and the crossover exponent φ are obtained as a function of the value n and...

The various types of magnetizations of a four-sublattice mixed-spin Heisenberg ferrimagnetic system are investigated with the help of the double-time temperature-dependent Green’s function technique. One obtains the first-order phase transitions from ferrimagnetic states to ferrimagnetic or...

The phase diagram of the Heisenberg ferromagnetic model in the presence of a magnetic random field (we have used bimodal distribution) of spin S=1/2 (quantum case) and S=∞ (classical case) on a simple cubic lattice is studied within the framework of the effective-field theory in finite cluster...

The dependence of the critical temperature Tc(ℓ,Δ) on film thickness ℓ and ratio of surface (Js) to bulk (Jb) exchange interaction strengths Δ≡(Js/Jb)−1 in quantum spin 12 Heisenberg model is studied by using the variational principle within the framework of the mean field...

The power series coherent anomaly method is applied to study the critical properties of a classical Heisenberg model. The values of true critical temperature Tc∗ are obtained. Using these results the estimation of critical exponent γ for the zero-field static susceptibility has been made. The...

We focus on the transition from quantum to classical behavior in thermodynamic functions and time correlation functions of a system consisting of three identical quantum spins s that interact via isotropic Heisenberg exchange. The partition function and the zero-field magnetic susceptibility are...

We investigate quantum teleportation using the entangled channel consisting of a two-qubit Heisenberg XYZ model with a nonuniform magnetic field in the presence of phase decoherence. It is shown that the initial state of the channel plays an important role in the fully entangled fraction and the...

The Handscomb Monte Carlo method is a powerful tool for the investigation of the critical properties of quantum spin models. The sample space in this technique is constructed over the space of ordered Mayer's diagrams and it is the diagrammatic series of the partition function that is calculated...

A special Heisenberg model is considered for which the exchange integral takes on the same value J not only for geometrically equivalent neighbours, but also for such j-neighbours which constitute an orbit of a “hidden” symmetry group of scaling transformations. The dispersion law for...

Boundary contributions of the magnetizations of several isotropic magnets, which are generalized antiferromagnetic Heisenberg models in open chains, are evaluated. The boundary magnetization approaches zero logarithmically as the external field goes to zero, in each of the models, namely the...