|Intercalation of a Co deposit between graphene and its substrate upon annealing. Magnetic contrast is prominently for magnetization perpendicular to the surface for 8 atomic layer Co films, as seen by spin-polarized low-energy electron microscopy.|
Strong motivations withstand the quest for carbon materials exploiting the spin of electron. First, the low spin-orbit and hyperfine interactions in carbon make the sp2 hybridized, highly conductive allotropes graphene and nanotubes, promising for efficient spin-transport. Second, the engineering of permanent magnetic moments in a naturally non ferromagnetic material such as graphene preludes a new class of low-cost, light and flexible magnetic materials. Hybrid materials combining graphene and metals give new degrees of freedom for achieving novel properties and functionalities. Net magnetic moments were obtained in Fe-contacted graphene, and large spin-splitting of the π-bands were reported for graphene in contact with a high atomic mass metal. Not yet exploited for magnetism or spintronics is the optical transmittance of graphene, which is suitable for optical switching or imaging of magnetization of a ferromagnet. Tuning the metallic films properties via an interface with graphene was little explored so far. This requires thin films whose interfaces are a prominent fraction.
Nanometer-thick Co deposits were intercalated at moderate temperature at the interface between graphene and its metallic substrate, Ir(111), yielding smooth Co films. Structural, electronic and magnetic characterizations by scanning tunneling microscopy diffraction, Auger electron spectroscopy, Raman spectroscopy, density functional theory, and spin-polarized low-energy electron microscopy, are provided. By comparing graphene-caped and -uncaped Co/Ir(111), it is found that the graphene/Co interface strongly favors perpendicular magnetization, presumably due to the interaction between graphene and Co. The magnetization is maintained perpendicular to the sample surface over a large range of thickness, until as much as 13 atomic layers, a larger thickness than in most metal capped Co films. Intercalation offers an efficient means for close-to-room temperature preparation of a new class of epitaxial hybrid materials, air-protected graphene/ferromagnetic stacks with tunable magnetic properties.