Ising-like model for the two step spin-crossover of binuclear molecules

We present a two-sublattice Ising-type model, involving one intramolecular interaction treated rigorously and intermolecular interactions treated in the mean-field approach, in order to describe the two-step transition exhibited by a bi-nuclear spin-crossover complex. Spontaneous symmetry breakings can be obtained according to the relative values of the interactions parameters. The phase diagram is given and the experimental data of [Fe(bt) (NCS)2]2bpym are treated in the present model. (orig.)