  Pressure-induced phase transitions of spin-crossover materials were simulated
by a Monte Carlo simulation in the constant pressure ensemble for the first
time. Here, as the origin of the cooperative interaction, we adopt elastic
interaction among the distortions of the lattice due to the difference of the
molecular sizes in different spin states, i.e., the high spin (HS) state and
the low spin (LS) state. We studied how the temperature dependence of the
ordering process changes with the pressure, and we obtained a standard sequence
of temperature dependences that has been found in changing other parameters
such as strength of the ligand field (S. Miyashita et al., Prog. Theor. Phys.
\textbf{114}, 719 (2005)). Various effects of pressure on the spin-crossover
ordering process are examined from a unified point of view.
