  The spin-dependent electronic structures of aluminum-(Al) doped zigzag
silicene nanoribbons (ZSiNRs) are investigated by first-principles
calculations. When ZSiNRs are substitutionally doped by a single Al atom on
different sites in every three primitive cells, they become half-metallic in
some cases, a property that can be used in spintronic devices. More
interestingly, spin-down electrons can be transported at the Fermi energy when
the Al atom is placed on the sub-edge site. In contrast, spin-up electrons can
be transported at the Fermi energy when the ZSiNRs are doped on sites near
their center. The magnetic moment on edge is considerably suppressed if the Al
atom is doped on edge or near-edge sites. Similar results are obtained for a
phosphorus-(P) and boron-(B) doped ZSiNR. When two or more Si atoms are
replaced by Al atoms, in general the half-metallic behavior is replaced by a
metallic, spin gapless semiconducting or semiconducting one. When a line of six
Si atoms, along the ribbon's width, are replaced by Al atoms, the spin
resolution of the band structure is suppressed and the system becomes
nonmagnetic.
