LATTICE STRUCTURE OF THE FULLERENE FERROMAGNET TDAE-C-60

IN the brief time since the development of techniques for the purification of condensed phases of C60 (refs 1, 2), compounds of C60 have been synthesized that exhibit the important solid-state properties of superconductivity 3,4 and ferromagnetism 5. The fact that the C60 molecule participates in these two disparate effects is in itself striking; furthermore, the C60-based material has the highest T(c) of any molecular organic ferromagnet 6. An understanding of the physical origin of this ferromagnetism is sure to require a knowledge of the crystal structure. Here we report on an X-ray diffraction study of the ferromagnet TDAE-C60, where TDAE is tetrakis(dimethylamino)ethylene, C2N4(CH3)8. We find that the composition is stoichiometric with 1:1 ratio of TDAE to C60. The structure has a c-centred monoclinic unit cell suggestive of an anisotropic, low-dimensional band structure. Any theory for the ferromagnetic behaviour will have to take this anisotropy into account.