Covalent-adsorption induced magnetism in graphene

Magnetism and the mechanism of magnetic coupling in graphene decorated with monovalent and divalent adsorbates were investigated using first-principles calculations based on spin polarized density functional theory. The effects of adsorption concentration and the electronegativity of the adsorbate species on the magnetic and electronic properties were analyzed. For monovalent chemisorptions, the magnetic order originates from the instability of π electrons induced by the adsorption, opening a narrow energy gap and resulting in antiparallel spin directions on adjacent carbon atoms on the graphene sheet. The magnetic order is only possible for the separation between the adsorbing sites less than 10 Å. On the contrary, divalent chemisorptions cause long-range magnetic coupling, which is originated from the exchange interactions between localized nonbonding π electrons (spin-polarized) mediated by the conduction π electrons around the Fermi energy, similar to the s–d interaction in transition metals. We demonstrate that our results are well consistent with recent experimental findings.