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Inducing and Optimizing Magnetism in Graphene Nanomesh

Using first-principles calculations, we explore the electronic and magnetic properties of graphene nanomesh (GNM), a regular network of large vacancies, produced either by lithography or nanoimprint. When removing an equal number of A and B sites of the graphene bipartite lattice, the nanomesh made mostly of zigzag (armchair) type edges exhibit antiferromagnetic (spin unpolarized) states. In contrast, in situation of sublattice symmetry breaking, stable ferri(o)magnetic states are obtained. For hydrogen-passivated nanomesh, the formation energy is dramatically decreased, and ground state is found to strongly depend on the vacancies shape and size. For triangular shaped holes, the obtained net magnetic moments increase with the number difference of removed A and B sites in agreement with Lieb's theorem for even A+B. For odd A+B triangular meshes and all cases of non-triangular nanomeshes including the one with even A+B, Lieb's theorem does not hold anymore which can be partially attributed to introduction of armchair edges. In addition, large triangular shaped GNM could be as robust as non-triangular GNMs, providing possible solution to overcome one of crucial challenges for the sp-magnetism. Finally, significant exchange splitting values as large as $\sim 0.5$ eV can be obtained for highly asymmetric structures evidencing the potential of GNM for room temperature carbon based spintronics. These results demonstrate that a turn from 0-dimensional graphene nanoflakes throughout 1-dimensional graphene nanoribbons with zigzag edges to GNM breaks localization of unpaired electrons and provides deviation from the rules based on Lieb's theorem. Such delocalization of the electrons leads the switch of the ground state of system from antiferromagnetic narrow gap insulator discussed for graphene nanoribons to ferromagnetic or nonmagnetic metal.