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...

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...

By using the differential operator technique and the effective field theory scheme we study the tricritical behavior of Heisenberg classical model of spin-12 in a random field. The phase diagram in the T–h plane on a square and simple cubic lattice for a cluster with two spins is obtained when...

We study kink states of quantum, ferromagnetic, easy axis spin 12 chains at zero temperature. These are produced by applying opposite magnetic fields on the two end sites of the chain. For sufficiently strong anisotropy and boundary field, we obtain estimates on the wave function of the lowest...

A semi-classical theory is employed to investigate the spin wave spectra and the localization profile of linear quasiperiodic binary superlattices, where one of their components is a ferromagnetic material, the other one being an antiferromagnet. The calculations are carried out for the...

We discuss some recent determinations of the equation of state for the XY and the Heisenberg universality class.

We present an exact diagonalization study of the half-filled Hubbard model on bipartite quasi-one-dimensional lattices. In particular, we emphasize the dependence of the ferrimagnetic ground state properties, and its associated magnetic excitations, on the Coulomb repulsion U.

A one-dimensional spin-12 antiferromagnetic Heisenberg model with multiple decorations is introduced. The low-lying properties of the decorated quantum spin chain are discussed. In the continuum and semiclassical limit of the present model, the non-linear sigma model with a topological term is...