Abstract
This paper presents our work on the investigation of the surface structure and the electronic and magnetic properties of the graphene layer on the lattice-matched surface of a ferromagnetic material, Ni(111). Scanning tunneling microscopy imaging shows that perfectly ordered epitaxial graphene layers can be prepared by elevated temperature decomposition of hydrocarbons, with domains larger than the terraces of the underlying Ni(111). In some exceptional cases, graphene films do not show rotational alignment with the metal surface, leading to moiré structures with small periodicities. We discuss the crystallographic structure of graphene with respect to the Ni(111) surface relying both on experimental results and on recent theoretical studies. X-ray absorption spectroscopy investigations of empty valence-band states demonstrate the existence of interface states, which originate from the strong hybridization between the graphene π and Ni 3d valence-band states with the partial charge transfer of the spin-polarized electrons to the graphene π* unoccupied states. The latter leads to the appearance of an induced magnetic moment of carbon atoms in the graphene layer, which is unambiguously confirmed by both x-ray magnetic circular dichroism and spin-resolved photoemission. Further angle-resolved photoemission investigations indicate a strong interaction between graphene and Ni(111), showing considerable modification of the valence-band states of Ni and graphene due to strong hybridization. A detailed analysis of the Fermi surface of the graphene/Ni(111) system shows very good agreement between experimental and calculated two-dimensional maps of the electronic states around the Fermi level, supporting the idea of spin-filtering. We analyze our spectroscopic results relying on the currently available band structure calculations for the graphene/Ni(111) system and discuss the perspectives of the realization of graphene/ferromagnet-based devices.
Highlights
Graphene is a two-dimensional sheet of carbon atoms arranged in a honeycomb lattice with two atoms in the unit cell [1, 2, 3]
The strong hybridization between graphene π and Ni 3d valence band states at the graphene/Ni(111) interface leads to the partial charge transfer of the spin-polarized electrons from Ni onto C with the appearance of an induced effective magnetic moment of carbon atoms [29] which can be detected in an experiment which is sensitive to the magnetic state of particular element, like x-ray magnetic circular dichroism (XMCD)
STM investigation shows that perfectly ordered epitaxial graphene layers can be prepared by elevated temperature decomposition of hydrocarbons, with domains larger than the terraces of the underlying Ni(111)
Summary
Graphene is a two-dimensional sheet of carbon atoms arranged in a honeycomb lattice with two atoms in the unit cell [1, 2, 3]. The spin-filtering effect originates form the unique overlapping of the electronic structures of the graphene monolayer and close-packed surfaces of ferromagnetic Ni and Co. As discussed earlier, graphene is a semimetal with electronic density in the vicinity of EF at corners (K points) of the hexagonal Brillouin zone of graphene (Fig. 2). If the Fermi surface projections of ferromagnetic metals, f cc Ni or Co, on the (111) close-packed plane are considered, in both cases graphene has only minority electron density around the K points of the surface Brillouin zone. Detailed analysis of the Fermi surface of the graphene/Ni(111) system indicates very good agreement between experimental and calculated 2D pictures of electronic states in the valence band
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