THE INFLUENCE OF THE LATTICE GEOMETRY ON THE THERMODYNAMICAL PROPERTIES OF 2-DIMENSIONAL SPIN SYSTEMS

Various types of mixed-spin two-dimensional Heisenberg network are inv estigated by means of Monte Carlo simulations. This study aims at inte rpreting quantitatively the thermodynamical properties of two-dimensio nal molecule-based magnets that have been recently synthesized. The pr oposed model requires that: (i) one of the two magnetic centres has a spin large enough to be treated as a classical spin; (ii) the zero-fie ld Hamiltonian is isotropic; (iii) the quantum spins have only classic al spins as neighbours. The quantum Hamiltonian is then replaced by a classical one with effective ferromagnetic interactions. The temperatu re dependence of both the specific heat and the magnetic susceptibilit y are calculated. The effects of the lattice geometry are analysed. We obtain for the specific heat a typical curve which is independent of these effects.