Charge transfer effects in Co-phthalocyanine single molecule magnets on graphene

In this thesis we investigated the electronic and magnetic coupling in hybrid graphene-single molecule magnets systems. This project is the result of a collaboration between the ESRF (European Synchrotron Radiation Facility) and the NANOsciences department of Istitut Néel, CNRS, Grenoble. Graphene samples have been produced using a chemical vapor deposition (CVD) technique that both allows to obtain large graphene areas and to transfer them on dielectric substrates (SiO2/Si++ and SrTiO3) in order to perform field effect measurements. The morphological and electrical characterization of our samples shows that they are formed by a single graphene layer with only a few percent of defected areas and intrinsic hole (graphene/SiO2/Si++) or electron (graphene/SrTiO3) doping. Cobalt phthalocyanine (CoPc) single molecule magnets have been deposited in-situ and at room temperature on graphene substrates and on a highly oriented pyrolytic graphite (HOPG) substrate used as a reference. The evaporation process has been calibrated in order to achieve a coverage of 10% of a monolayer of molecules on the surface. From X-ray absorption spectroscopy measurements (X-ray magnetic circular dichroism and X-ray linear dichroism) we found that CoPc molecules do not interact with HOPG or hole doped graphene, so that the free molecule electronic ground state is retained. Opposite to that, evidence of a charge transfer effect from the substrate is observed in CoPc deposited on electron doped graphene, resulting in an almost complete quenching of the magnetic moment associated to the central cobalt ion. These results are similar to experimental results and theoretical models for CoPc deposited on metals but in addition suggest the possibility of progressively controlling the magnetic moment of CoPc just by changing the density of carriers at the Fermi level in graphene.