Macroscopic methods: Magnetic, optical, and calorimetric techniques

The recent effervescent impetus in the spin transition research field is associated with the prodigious multidisciplinary effort that is carried out by different research groups all over the world. Indeed, more and more groups are working in this exciting research field. Nevertheless, this renewed interest also reflects the evolution of the characterization techniques that have been used since the earliest studies of these molecular-based switchable materials. Indeed, we have passed from traditional characterization methods such as UV–vis and Mössbauer spectroscopy or torque magnetometers to the most advanced techniques that are even capable to monitor a spin transition in a single molecule (e.g., X-ray diffraction, X-ray photoelectron spectroscopy, scanning tunneling microscopy, etc.). In this study, we will focus on the basis and the evolution of three critical macroscopic tools, i.e. the optical, magnetic, and calorimetric characterization methods.