Bistability effects in solvent-including metallofullerene crystals

Magnetic bistability has been discovered in the low temperature properties of the solvent-including metallofullerene single crystals Ln@C 82 (CS 2 ) 1.5 {Ln = La, Ce}. In these insulating compounds a single paramagnetic spin is localized on the fullerene cage at room temperature. Control of the cooling rate through an observed transition at ∼ 150K results in either quenching or persistence of the fullerene spin and antiferromagnetic interactions at low temperatures. This bistability seems to be a common phenomena in metallofullerenes. This paper presents a low temperature x-ray diffraction investigation of the crystals, however no evidence of a structural phase transition has been found that could have been the origin of the bistability.