Spin-crossover molecular materials

The spin-crossover phenomenon may provide the most spectacular example of molecular bistability. Some transition metal compounds present a crossover between a low-spin and a high-spin state. The transition between these two states may be induced by a variation of temperature, of pressure, or by light irradiation. Up to now, three approaches have been explored with the objective of using spin-crossover compounds as active elements of memory devices. These approaches are the thermal addressing of compounds showing a wide hysteresis loop around room temperature, the light-induced excited spin-state trapping, and the ligand-driven light-induced spin change. Other types of transition between two spin states, based on other mechanisms, have recently been discovered. The understanding of these mechanisms offers many opportunities to theoreticians.