  A type of line defect (LD) composed of alternate squares and octagons (4-8)
as the basic unit is currently an experimentally available topological defect
in graphene lattice, which brings some interesting modification to magnetic and
electronic properties of graphene. The transitional metal (TM) adsorb on
graphene with line-defect (4-8), and they show interesting and attractive
structural, magnetic and electronic properties. For different TMs such as Fe,
Co, Mn, Ni and V, the complex systems show different magnetic and electronic
properties. The TM atoms can spontaneously adsorb at quadrangular sites,
forming an atomic chain along LD on graphene. The most stable configuration is
hollow site of regular tangle. The TMs (TM = Co, Fe, Mn, Ni, V) tend to form
extended metal lines, showing ferromagnetic (FM) ground state. For Co, Fe, and
V atom, the system are half-metal. The spin-{\alpha} electron is insulating,
while spin-\b{eta} electron is conductive. For Mn and Ni atom, Mn-LD and Ni-LD
present spin-polarized metal; For Fe atom, the Fe-LD shows semimetal with Dirac
cones. For Fe and V atom, both Fe-LD and V-LD show spin-polarized half-metallic
properties. And its spin-{\alpha} electron is conducting, while spin-\b{eta}
electron is insulating. Different TMs adsorbing on graphene nanoribbon forming
same stable configurations of metal lines, show different electronic
properties. The adsorption of TMs introduces magnetism and spin-polarization.
These metal lines have potential application in spintronic devices, and work as
quasi-one-dimensional metallic wire, which may form building blocks for
atomic-scale electrons with well-controlled contacts at atomic level.
