We apply the classical Preisach model to reproduce the major and minor thermal hysteresis loops in the high-spin ↔ low-spin transition for [Fe(btr)2(NCS)2]H2O and Fe(bt)2(NCS)2 (bt = 2,2′-bi-thiazoline). For this purpose, we consider that spin transition occurs through spin domains which are characterized by the up and down switching temperatures Tα and Tβ of a square-shaped thermal hysteresis loop. For each compound, we determine a Gaussian Preisach distribution P(Tα,Tβ) which fits the experimental data. © 1998 IEEE.