A two-sublattice model for light-induced hysteresis in spin-crossover solids: symmetry breaking and kinetic effects

The recently developed macroscopic model of light-induced equilibrium of sp in-crossover solids is extended to the case of two equivalent sublattices c oupled 'antiferromagnetically' To do this, we use an Ising-like model invol ving two coupling parameters of opposite signs for the intra- and inter-sub lattice interactions, previously introduced to describe the two-step static spin transition, and we have adapted the macroscopic master equation descr ibing the time evolution of the system accordingly. We mostly report on the quasi-static solutions of the system, under constan t light irradiation and for slow temperature variations. Light-induced ther mal hysteresis loops are obtained and have typical two-step shapes for suit able sets of parameter values. The model predicts, in analogy with the stat ic transition, a possible light-induced symmetry breaking between the struc turally equivalent sublattices. Kinetic effects are briefly described.