Spin crossover compounds show a first order phase transition that can be accompanied by a thermal hysteresis. In this paper we present the analogies between this class of substances and magnetic systems with a domain structure. We show the possibilities of study the thermal hysteresis of spin crossover solids using Preisach-type models and of the First Order Reversal Curves (FORC) method. Experimental FORC diagrams were obtained for pure and diluted spin transition system [FexZn1-x(btr)2(NCS) 2]H2O, where x governs, through cooperative interactions, the width of the thermal hysteresis loops. A parametrical identification of the distributions corresponding to inter-domains interactions domain size was performed also using an Ising like model.