Magnetism of an Ru adlayer on graphite

Using a tight-binding Hubbard model within the unrestricted Hartree-Fock approximation we study the ground state electronic and magnetic structure of an Ru monolayer epitaxially adsorbed on graphite. Pfandzelter et al. (R. Pfandzelter, G. Steierl and C, Rau, Phys. Rev. Lett., 74 (1995) 3467; G. Steierl, R. Pfandzelter and C. Rau, J. Appl. Phys., 76 (1994) 6431) have recently studied this system experimentally and they observed ferromagnetism at temperatures below 250 K. By comparison with an isolated Ru monolayer which has the same structure as the adlayer we discuss the role of the graphite substrate.