Theoretical study of magnetic interaction between C60 anion radicals

The magnetic interactions between two C60 anions are investigated by using unrestricted B3LYP (UB3LYP) calculations. Among four types of interactions, only one type of SOMO–SOMO interaction shows a week ferromagnetic interaction (Jab = 4.6 cm−1) whilst other interactions show week anti-ferromagnetic interactions. In order to explain a mechanism of the ferromagnetic and the anti-ferromagnetic interactions, a natural orbital (NO) analysis and a spin density analysis are carried out. The results of the analyses suggest that orbital orthogonality between SOMOs of each C60 anions is the origin of the ferromagnetic interaction. On the other hand, a spin polarization effect does not appear in a spin density map in the ferromagnetic coupling state.