The magnetic response of magnetic insulators is determined by the coupling between the magnetic moments, which is usually temperature independent. A theoretical work dating from the 1980s showed that the eventual temperature dependence originates from the thermal expansion of the lattice, while the contribution of the lattice vibrations could be considered negligible. In contrast, Martin Klanjšek and Denis Arčon from the Condensed Matter Physics department at the Jožef Stefan Institute, together with German colleagues who synthesized the sample, showed that the magnetic coupling in caesium superoxide is strongly temperature dependent, precisely as a result of the librations of the magnetic superoxide molecules. This first confirmation of the dynamic modulation of the magnetic coupling, a prototypical phenomenon relevant for a range of other molecular magnets, is described in the recently published article in Physical Review Letters.