  We report a first-principles electronic-structure calculation on C and BN
hybrid zigzag nanoribbons. We find that half-metallicity can arise in the
hybrid nanoribbons even though stand-alone C or BN nanoribbon possesses a
finite band gap. This unexpected half-metallicity in the hybrid nanos-tructures
stems from a competition between the charge and spin polarizations, as well as
from the pi orbital hybridization between C and BN. Our results point out a
possibility of making spintronic devices solely based on nanoribbons and a new
way of designing metal-free half metals.
