After the discovery of the phenomena of light-induced excited spin state trapping (LIESST), the functional properties of metal complexes have been studied intensively. Among them, cooperative phenomena involving low spin-high spin (spin-crossover) transition and magnetic ordering have attracted interests, and it has become necessary to formulate a unified description of both phenomena. In this ...

We develop a transfer matrix method to compute exactly the spin-spin correlation functions < s0sn > of Bethe lattice spin models in the external magnetic field h and for any temperature T . We first compute < s0sn > for the most general spin S Ising model, which contains all possible single-ion and nearest-neighbor pair interactions. This general spin S Ising model includes the spin-1/2 simple ...

We show here for the one-dimensional spin-1/2 axial-next-to-nearest-neighbor Ising model in an external magnetic field that the linear density of Yang-Lee zeros may diverge with critical exponent σ=-2/3 at the Yang-Lee edge singularity. The necessary condition for this unusual behavior is the triple degeneracy of the transfer-matrix eigenvalues. If this condition is absent we have the usual val...