Low-temperature bistability in the magnetic properties of solvent-including lanthanide metallofullerene crystals

Single crystals of the endohedral La@C-82(CS2)(1.5) have been investigated by ESR, SQUID, and optical absorption measurements. We find that the crysta l is a localized paramagnet at room temperature with evidence of strong ant iferromagnetic interactions (theta similar to-130 K). ESR spectroscopy reve als evidence of a phase transition at 150 K, that we assign to be an orient ational ordering transition of the fullerene molecules. Furthermore, at low temperatures we find a magnetic bistability that can be controlled by the cooling rate. Investigations of Ce@C-82(CS2)(1.5) reveal evidence of simila r bistability and hence we postulate that it is a common phenomena in these endohedrals.