Family-dependent magnetism in atomic boron adsorbed armchair graphene nanoribbons†
Non-metallic atom adsorption has been proven to be a stable approach to introduce net magnetism in graphene. Here, we investigated electronic structures and magnetic properties of armchair graphene nanoribbons with chemisorption of atomic boron (B-AGNRs) by performing first principles calculations. The results show that although previous experiments show that adsorption of B can induce a high net magnetism in graphene, the cutting of such magnetic graphene cannot always result in magnetic ribbons. Only the ribbons in the family of width W = 3p + 1 are magnetic with a magnetic moment of 1.0 μB, which is insensitive to the adsorption positions, ribbon widths, and supercell lengths. The ribbons in the two other families of W = 3p and 3p + 2 are nonmagnetic. It is revealed that different from substitutional B-doping, which leads to the Fermi level shifting to the valence band (VB), the B-adsorption raises up the Fermi level, and the coupled pz orbitals of the B and nearby C atoms induce a partially-filled energy band (PFEB) present in each ribbon. The distribution of the PFEB is totally family-dependent. It is very delocalized for W = 3p or 3p + 2 but it is localized for W = 3p + 1 due to the strong quantum confinement and edge effects. Moreover, the localization can be heavily enhanced by decreasing the ribbon width and increasing the supercell length, due to the enhanced quantum confinement and the weakened interaction between adatoms. The heavily localized PFEB locates right at the Fermi level, which is hindered due to the Coulomb repulsion and thus spin-splitting occurs spontaneously, resulting in the magnetic semiconducting characteristics. Our findings provide not only a promising one-dimensional material for developing spin-devices in semiconductor spintronics, but also fundamental insights into the magnetic behavior of the non-metallic atoms adsorbed AGNRs.