Magnetic exchange interaction between pi-electron radicals adsorbed on graphites

The nature and the magnitude of the magnetic exchange interaction between o rganic pi radicals adsorbed on quasi-1-D graphites and 2-D graphite cluster s are investigated theoretically. The interaction between the pi centers of the radicals and the graphite surface determines the common re system of c onjugation, and the intermolecular exchange coupling of electrons within a narrow half-filled band of degenerate or quasi-degenerate MOs. The main com ponent of the ferromagnetic exchange interaction is the Coulomb (Hund) exch ange and a smaller contribution comes from the indirect exchange. The therm odynamic treatment of a 2-D model system of radicals adsorbed on graphite w ithin the Ising model shows macroscopic spin S and spontaneous magnetizatio n at T not equal 0 K. (C) 2000 Elsevier Science B.V. All rights reserved.