  Towards spin selective electronics made of three coordinated carbon atoms,
here we computationally propose robust and reversibly bias driven evolution of
pristine undoped graphene nano-ribbons(GNR) into ferromagnetic-semiconductor,
metal or a half metal, irrespective of their edge configurations. The evolution
is a result of a rare ferromagnetic(FM) order emerging among nearest
neighbouring(n-n) sites, in positively biased regions in their in-homogeneous
bias unit-cells, in attempt to cooperatively minimise on-site Coulomb repulsion
and kinetic energy, while maximising localization of electrons at the
positively biased sites. The phenomenon appears to be a general property of
in-homogeneously biased Coulomb correlated bipartite systems. Consequences are
particularly rich in zigzag edged graphene nano-ribbons(ZGNR) due to the
contest of bias driven n-n FM order and the inter-edge antiferromagnetic order
inherent to ZGNRs, leading to systematic closing of gap for one of the spins,
amounting to bias controlled unmissable opening of window for FM-semiconducting
and half-metallic transport.
