A Monte Carlo simulation for intermolecular interaction of 2D spin-crossover compounds using the Ising-like model

Spin-crossover (SCO) complexes show the SCO phenomenon: a remarkable bistability between diamagnetic low spin (LS) and paramagnetic high spin (HS) states depending on several parameters such as temperature, light, magnetic field, pressure, etc. In recent years, owing to the marked transformation of magnetic properties, colors, and molecular structures of transition metal complexes following the SCO phenomenon, SCO complexes have been attracting much attention for technological applications, e.g., high-density information storage, display devices, and micro-sensors. The purpose of this study is to clarify the influence of intermolecular interaction on the phase transition. To evaluate the model and clarify intermolecular interaction on phase transition, we perform Monte Carlo simulation of 2D SCO complexes using Ising like model and calculate differences of magnetic susceptibility curves due to particle size and shape of SCO complex.
In small system, a smooth transition without hysteresis appears. As the particle size increases, the transition temperature shifts towards the higher temperature region and the hysteresis width becomes wider. These size dependencies reproduce that reported experimentally.