FERROMAGNETIC INTERACTION IN C-60 CHARGE-TRANSFER COMPLEXES

C-60[TDAE] was the first and so far the only C-60 CT complex which exh ibits molecular ferromagnetism with a Curie temperature of about 16 K [1]. Despite extensively investigated a convincing access to the origi n of the low temperature phase of this C-60 CT complex is still missin g. The 3 fold degeneracy of the C-60 HOMO is lifted by a change of the C-60 conformation, and we find a transition from a static low tempera ture Jahn-Teller distortion to a dynamic one at about 140 K. The exces s electron is concentrated in a belt around the equator of the C-60(-) The distorted C-60 molecules have a spin density distribution with an axial symmetry and are aligned along the crystallographic axes. This orientational ordering of the C-60(-) molecules is the necessary precu rsor to a ferromagnetic spin glass type ordering in C-60[TDAE] which w as interpreted in terms of spin polarisation between C-60(-.) and TDAE (+.) by Yamaguchi et al [2].