Ising-like model applied to a triangular lattice of 2D spin-crossover nanoparticles: Evidence of a re-entrant phase transition

We consider a 2D spin crossover (SCO) nanoparticles configuration under the influence of an external environment. Each nanoparticle is at the vertex of a triangular lattice leading to hexagonal-shaped systems. Each molecule located in the bulk is then connected to six nearest-neighbours (nn) while those situated at the surface have three or four nn. Adapting the entropic sampling Monte Carlo method, using three parameters: n HS (the total high spin fraction), s (the correlation: the sum of nn interactions the molecules) and n s HS (the high-spin fraction at the surface), we determined the density of macrostates D(nHS, n s HS,s) by scanning the full spin configurations. This information is then used to analyse the thermal behaviour of the system taking into account for the short- (J) and long-range (G) interactions as well for the interactions (L) between the molecules at the surface and the matrix (environment). The present contribution is devoted to the investigations of the required physical conditions which allow this triangular 2D lattice to exhibit a re-entrant phase transition, in particular when the size of the nanoparticles is reduced.