RESUMO
A comprehensive experimental and theoretical study of both thermal-induced spin transition (TIST) as a function of pressure and pressure-induced spin transition (PIST) at room temperature for the two-dimensional Hofmann-like SCO polymer [Fe(Fpz)2Pt(CN)4] is reported. The TIST studies at different fixed pressures have been carried out by magnetic susceptibility measurements, while PIST studies have been performed by means of powder X-ray diffraction, Raman, and visible spectroscopies. A combination of the theory of elastic interactions and numerical Monte Carlo simulations has been used for the analysis of the cooperative interactions in TIST and PIST studies. A complete (T, P) phase diagram for the compound [Fe(Fpz)2Pt(CN)4] has been constructed. The critical temperature of the spin transition follows a lineal dependence with pressure, meanwhile the hysteresis width shows a nonmonotonic behavior contrary to theoretical predictions. The analysis shows the exceptional role of the total entropy and phonon contribution in setting the temperature of the spin transition and the width of the hysteresis. The anomalous behavior of the thermal hysteresis width under pressure in [Fe(Fpz)2Pt(CN)4] is a direct consequence of a local distortion of the octahedral geometry of the Fe(II) centers for pressures higher than 0.4 GPa. Interestingly, there is not a coexistence of the high- and low-spin (HS and LS, respectively) phases in TIST experiments, while in PIST experiments, the coexistence of the HS and LS phases in the metastable region of the phase transition induced by pressure is observed for a first time in a first-order gradual spin transition with hysteresis.
RESUMO
The qualitative analysis of the spin-crossover molecular solid with distortion effect is presented. A spin-crossover solid with effect of distortion is studied in the framework of the Ising-like model with two-order parameters under statistical approach, where the effect of elastic strain on inter-ion interaction is considered. These considerations lead to examination of the relation between the primary and secondary order parameters during temperature and pressure changes.
RESUMO
The thermal transition accompanied by the variation of the molecular volume in nanoparticles of spin-crossover materials has been studied on the basis of microscopic Ising-like model solved using Monte Carlo methods. For considered model, we examined the spin-crossover phenomenon with applied hydrostatic pressure and thus was shown the possibility to shift transition temperature toward its room value. The obtained results of numerical simulations are in agreement with the experimental ones.