Nanostructural magnetism of polymeric fullerene crystals

Abstract

The nature of magnetism in all-carbon crystals composed of polymeric layers of covalently bound fullerene (C60) molecules is considered. The results of quantum-chemical calculations performed using the unrestricted Hartree-Fock approximation and the semiempirical AM1 method are presented. It is shown that the exchange integrals J of both a free C60 molecule and a monomer unit of the polymer are too large ensure the required magnetic susceptibility of the fullerene crystal. However, the J value exhibits an approximately n-fold decrease for an oligomer molecule consisting of n C60 units. Therefore, in the case of large n, the exchange integral can be reduced to a low level sufficient to provide for a significant magnetic susceptibility. A nanosize (scaly) model of the observed magnetism is proposed that is consistent with recent experimental data, which are indicative of a nanostructural character of magnetic fullerene samples.