Ferromagnetic versus molecular ordering in C-60 charge transfer complexes

[TDAE] C-60 (TDAE, tetrakis( dimethylamino) ethylene) was the first and is so far the only C-60 charge transfer complex, which exhibits molecular ferromagnetism with a Curie temperature of about 16 K. Though extensively studied a convincing access to the origin of the low-temperature phase is still missing. Three mechanisms for the ferromagnetism will be compared: the classical Heisenberg ferromagnet, configuration interaction and spin polarization. The role of molecular ordering and of the Jahn-Teller distortion of C-60 will be discussed.