Intrinsic effects of the boundary condition on switching processes in effective long-range interactions originating from local structural change

We investigated domain growth in switching processes between the low-spin and high-spin phases in thermally induced hysteresis loops of spin-crossover (SC) solids. Elastic interactions among the molecules with different volumes induce effective long-range interactions, and thus the boundary condition plays a significant role in the dynamics. In contrast to SC systems with periodic boundary conditions, where uniform configurations are maintained during the switching process, we found that domain structures appear with open boundary conditions. Unlike Ising-type models with short-range interactions, domains always grow from the corners of the system. The present clustering mechanism is universal for materials with the volume change in the unit molecule, and it provides an insight into the switching dynamics of their nanoscale systems.