Comparison of static and light-induced thermal hystereses of a spin-crossover solid, in a mean-field approach†

We investigate the relationship between the two mean-field models which have been proposed independently for characterizing the static and the light-induced thermal hystereses of spin-transition solids, respectively involving an interaction parameter J and a relaxation self-acceleration parameter α. We unify these two models into a unique - static and dynamic - mean-field description based on Arrhenius thermal activation processes. The model is used to analyse the experimental hysteresis loops, the relaxation curves in the dark, and the light-induced instability in the spin-crossover system [Fe x Co 1- x (btr) 2 (NCS) 2 ]H 2 O. A linear relationship between J and α T is obtained, which is in qualitative agreement with the available theories.