  The dramatic changes in electronic and magnetic properties are investigated
using the first-principles calculations for (Cl, Br, I, At)-adsorbed graphene
nanoribbons. The rich and unique features are clearly revealed in the
adatom-dominated band structures, p-type doping, spin arrangement/magnetic
moment, spatial charge distribution, and orbital- and spin-projected density of
states. Halogen adsorptions can create the non-magnetic, ferromagnetic or
anti-ferromagnetic metals, being mainly determined by concentrations and edge
structures. The number of holes per unit cell increases with the adatom
concentrations. Furthermore, magnetism becomes nonmagnetic when the adatom
concentration is beyond 60 % adsorption. There are many low-lying
spin-dependent van Hove singularities. The diversified properties are
attributed to the significant X-C bonds, the strong X-X bonds, and the adatom-
and edge-carbon-induced spin states.
