Spatiotemporal Investigations on Light-Driven High-Spin–Low-Spin Interface Dynamics in the Thermal Hysteresis Region of a Spin-Crossover Single Crystal

Abstract

We have investigated by optical microscopy the thermal spin transition of a single crystal of the spin-crossover compound [{Fe(NCSe)(py)2}2(m-bpypz)] under various shining intensities, far from the light-induced spin-state trapping region. We found evidence of photoheating on the thermally induced hysteretic response of the crystal, leading to the control of the transition temperature and the hysteresis width as a function of the light intensity. The inspections of the spatiotemporal behaviors of the spin-crossover transition, on heating and cooling, have also evidenced a significant dependence of the propagation speed of the high-spin–low-spin interface on the intensity of light. In particular, for strong shining intensities, a slowing of the interface speed at the transition is obtained, and an unprecedented dynamical two-step-like transition was observed in the thermal hysteresis. These results are analyzed theoretically using a spatiotemporal approach based on reaction–diffusion equations including th...