Magnetic exchange interaction between π-electron radicals adsorbed on graphites Original Research Article

The nature and the magnitude of the magnetic exchange interaction between organic π radicals adsorbed on quasi-1-D graphites and 2-D graphite clusters are investigated theoretically. The interaction between the π centers of the radicals and the graphite surface determines the common π system of conjugation, and the intermolecular exchange coupling of electrons within a narrow half-filled band of degenerate or quasi-degenerate MOs. The main component of the ferromagnetic exchange interaction is the Coulomb (Hund) exchange and a smaller contribution comes from the indirect exchange. The thermodynamic treatment of a 2-D model system of radicals adsorbed on graphite within the Ising model shows macroscopic spin S and spontaneous magnetization at T≠0 K.