Adding magnetic functionalities to epitaxial graphene by self assembly on or below its surface

We show how to add magnetic functionalities to graphene's set of extraordinary electronic, mechanical or optical properties. We will discuss such two examples: \begin{enumerate} \item \textit{Achieving long range magnetic order on a monolayer of TCNQ adsorbed on graphene /Ru(0001). } \end{enumerate} Cryogenic STM and Spectroscopy and DFT simulations show that isolated TCNQ molecules deposited on gr/Ru(0001) [1-3] acquire charge from the substrate and develop a sizeable magnetic moment, which is revealed by a prominent Kondo resonance. The self-assembled molecular monolayer develops spatially extended spin-split electronic bands with only the majority band filled, thus becoming a 2D organic magnet whose predicted spin alignment in the ground state is visualized by spin-polarized STM at 4.6 K [4]. The long range magnetic order is originated by the charge transfer from graphene to TCNQ (which creates the magnetic moments) \underline {plus} the self-assembly of the molecular adlayer on the graphene layer (which creates spin-polarized intermolecular bands where the added electrons partly delocalize). Examples will be shown where the adsorbed molecules accept charge and develop magnetic moments, but do nor form bands (F4-TCNQ on graphene/Ru(0001)), or where similar bands do form, but they are not populated, because there is no charge transfer to the molecules (TCNQ on gr/Ir(111)). ii) \textit{Introducing a giant spin-orbit interaction on graphene/Ir(111) by intercalation of Pb.} The intercalation of an ordered array of Pb atoms below graphene results in the appearance a series of equally spaced, sharp peaks in the differential conductance, as revealed by STS at 4.6 K. The vicinity of Pb enhances the, usually negligible, spin-orbit interaction of graphene. The spatial variation of the spin-orbit coupling creates a gauge field that acts as an pseudo magnetic field opening a gap, confining electrons and originating pseudo Landau levels [5].\\[4pt] [1] A.L. V\'{a}zquez de Parga et al, Phys. Rev. Lett. \underline {100}, 056807 (2008);\\[0pt] [2] B. Borca et al, Phys. Rev. Lett. \underline {105}, 036804 (2010);\\[0pt] [3] D. Stradi et al, Phys. Rev. Lett. \underline {106}, 186102 (2011);\\[0pt] [4] M. Garnica et al, Nature Physics \underline {9}, 368 (2013);\\[0pt] [5] F. Calleja et al, in preparation.