We propose a method to characterize quasi-periodic chains, based on the transmission probabilities. We consider finite layers which are building up following the Fibonaci, Thue-Morse and Cantor sequences. The spectra show an undoubtedly fractal behavior, with a distinct appearence for each...

The Lieb–Schupp inequality is the inequality between ground state energies of certain antiferromagnetic Heisenberg spin systems. In our paper, the numerical value of energy difference given by Lieb–Schupp inequality has been tested for spin systems in various geometries: chains, ladders and...

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...

Analytical solutions for the time-dependent autocorrelation function of the classical and quantum mechanical spin dimer with arbitrary spin are presented and compared. For large spin quantum numbers or high temperature the classical and the quantum dimer become more and more similar, yet with...

The transition behaviour of a magnetic system consisting of numerous nano-sized clusters with a zero external field was studied. We investigated the transition from superparamagnetism (SP) to ferromagnetic single-domain (SD) state due to the increase of cluster size by Monte Carlo simulation of...

We have extended the application of quantum renormalisation group (QRG) to the anisotropic Heisenberg model with next-nearest neighbour (n-n-n) interaction. The second order correction has to be taken into account to get a self similar renormalised Hamiltonian in the presence of...

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...