Due to the predominantly surface character of graphene, it is highly suitable for functionalization with external atoms and/or molecules leading to a plethora of new and interesting phenomena. Here we show ferromagnetic properties of hydrogenfunctionalized epitaxial graphene on SiC. Ferromagnetism in such a material is not directly evident as it is inherently composed of only non-magnetic constituents. Our results nevertheless show strong ferromagnetism, which cannot be explained by simple magnetic impurities. The ferromagnetism is unique to hydrogenated epitaxial graphene on SiC, where interactions with the interfacial buffer layer play a crucial role. We argue that the origin of the observed ferromagnetism is governed by electron correlation effects of the narrow Si-dangling-bond (Si-DB) states in the buffer layer exchangecoupled to localized states in the hydrogenated graphene layer. This forms a quasithree-dimensional ferromagnet with a Curie temperature higher than 300 K.Owing to its capability of ballistic transport over micrometer distances 1 , as well as its very long spin relaxation time and spin relaxation length 2, 3 , graphene represents a close-to-ideal material for spintronic applications 4 . In this context, considerable effort has recently been directed to rendering graphene ferromagnetic via chemical modification. Thus far, ferromagnetic order in graphene has been attained through covalent functionalization, involving the linkage of radical species like the spin-bearing carbon atom of an organic molecule or hydrogen atoms to the graphene layer [5][6][7][8][9][10][11][12][13][14][15][16][17] . Along these lines, functionalization of epitaxial graphene by aryl radicals has been reported to yield disordered magnetism, comprising a mixture of ferromagnetic, superparamagnetic and antiferromagnetic regions 18 .With the aid of combined atomic and magnetic force microscopy, it could be proven that these randomly dispersed regions are constituted by the attached moieties. This lack of a periodic functionalization pattern of the graphene sheet prevents the achievement of long range ferromagnetic order, thus limiting the use of such samples in spintronic devices.Furthermore, room temperature ferromagnetism has been detected in partially hydrogenated epitaxial graphene grown on silicon carbide (SiC), and attributed to hydrogen monomers bonded to the graphene sheet 12 . Despite these accomplishments, however, both the mechanism underlying the ferromagnetic ordering, and the role played by the SiC substrate used for the epitaxial graphene growth, has not yet been clarified. Here, we experimentally demonstrate that spin ordering within hydrogenated epitaxial graphene critically depends on the presence of the underlying buffer layer. In addition, it is shown that the created magnetic 3 areas are distributed over the entire graphene sheet, thus enabling to effectively tune the overall magnetization through the density of attached hydrogen atoms.To explore the ferromagnetism in epitaxial graphene, we use samples ...

Graphene antidot lattices (GALs) offer an attractive approach to band-gap engineering in graphene. Theoretical studies indicate that the size of the opened gap is sensitive to the shape, size, and architecture of the nanoholes introduced into the graphene sheet. We have investigated the temperature-dependent electrical conductivity of GALs comprising 50-nm-diameter nanoholes with a pitch of 80, 100, and 200 nm, respectively. The data reveal the presence of localized states within a transport gap, whose interactions lead to a soft Coulomb gap and associated Efros-Shklovskii variable range hopping (ES-VRH). This conduction type is preserved upon application of magnetic fields up to 1 Tesla, above which a transition to Mott variable range hopping occurs. Such a crossover can alternatively be introduced at zero magnetic fields by increasing either the nanohole spacing or the gate-controlled carrier concentration. Furthermore, at intermediate magnetic fields, the hopping exponent assumes a value of 2/3, as predicted by percolation theory for ES-VRH under this condition.

We investigate the low temperature electrical transport mechanism in graphene antidot lattices. While the antidot diameter is kept constant at 50 nm, the center-to-center spacing between the antidots is varied from 80 to 200 nm in cubic arrangement. Our temperature dependent charge transport data reveal that electrical conduction in the samples is governed by variable range hopping (VRH) between localized states within a band gap. Upon decreasing the nanohole spacing the localization becomes stronger and the transport mechanism changes from 2D Mott VRH to Efros-Shklovskii (ES VRH). Concomitantly, a soft gap emerges due to the stronger localization and the increased Coulomb interactions between the localized states, which are most likely located at the nanohole edges. The Coulomb gap (CG) decreases linearly with increasing charge carrier density. Stronger localization with an increased CG is observed for thermally annealed samples with reduced doping.

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