Magnetic phase transitions in an electroelastic model for magnetically ordered spin-crossover solids

Abstract

Spin-crossover and Prussian blue analog materials are investigated in two dimensions with the three-state Blume-Emery-Griffiths model where each spin interacts with its nearest neighbors and next-nearest neighbors and may be either in high-spin or low-spin state. The interactions through the system are strongly dependent on the instantaneous distance between atoms and are magnetic and elastic in nature. Finite-size effects have been detected at finite temperature on the model. The thermal distortion of the lattice configuration due to lattice unit displacements strengthened the thermal spin transition that occurred. The generated numerical results are obtained by two-step Monte Carlo simulations where used thermodynamic parameters allowed to establish a rich phase diagram. Gradual and first-order transitions with thermally induced hysteresis phenomena have been observed. Near the thermal hysteresis loops, the model exhibits throughout relaxation curves lattice configurations evolving through two-dimensional nucleation and growth processes that are enhanced with suitable values of the model parameters.