Dynamically fluctuating electric dipole moments in fullerene-based magnets

We report here the direct evidence of the existence of a permanent electric dipole moment in both crystal phases of a fullerene-based magnet - the ferromagnetic α -phase and the antiferromagnetic α⠀2-phase of tetra-kis-(dimethylamino)-ethylene-C 60 (TDAE-C 60) - as determined by dielectric measurements. We propose that the permanent electric dipole originates from the pairing of a TDAE molecule with surrounding C 60 molecules. The two polymorphs exhibit clear differences in their dielectric responses at room temperature and during the freezing process with dynamically fluctuating electric dipole moments, although no difference in their roomerature structures has been previously observed. This result implies that two polymorphs have different local environment around the molecules. In particular, the ferromagnetism of the α -phase is founded on the homogeneous molecule displacement and orientational ordering. The formation of the different phases with respect to the different rotational states in the Jahn-Teller distorted C 60 s is also discussed.