  We predict intrinsic half-metallicity in armchair boron nitride nanoribbons
(ABNNRs) via edge fluorination. The stability, electronic and magnetic
properties of bare and edge fluorinated ABNNRs have been systematically
analyzed by means of first-principles calculations within the local
spin-density approximation (LSDA). The ribbons whose only edge-B atoms
passivated with F atoms (i.e., edge-N atoms are un-passivated), regardless of
width, are found half-metallic with a half-metal gap of 0.3 eV. A 100 \% spin
polarized charge transport across the Fermi level is expected for such ribbons
as the spin polarized states are $\sim$0.4 eV more stable than the spin
un-polarized states and only single-spin conducting channels are present across
the Fermi level owing to the gigantic spin splitting. The existence of
half-metallicity is attributed to the localization of electronic charge at bare
edge-N atoms as revealed from the analysis of Bloch states and projected
density of states (PDOS).The sufficiently large half-metal gap (0.3 eV) with
huge difference in the energies ($\sim$ 0.4 eV) of spin polarized and spin
compensated states projects these half-metallic ABNNRs as potential candidate
for spintronics applications.
