  Fe-based devices are widely used in spintronics because of high
spin-polarization and magnetism. In this work, free-standing Fe atomic chains
were proposed to be used as the thinnest wires to generate spin-polarized
currents due to the spin-polarized energy bands. By ab initio calculations, the
zigzag structure was found more stable than the wide-angle zigzag structure and
has higher ratio of spin-up and spin-down currents. By our theoretical
prediction, Fe atomic chains have sufficiently long thermal lifetime only at
T<=150 K, while C atomic chains are very stable even at T=1000 K. This result
means that the spintronic devices based on Fe chains could only work at low
temperature. A system constructed by a short Fe chain sandwiched between two
graphene electrodes was proposed as a spin-polarized current generator, while a
C chain does not have such property. The present work may be instructive and
meaningful to further practical applications based on recent technical
development on the preparation of metal atomic chains [Proc. Natl. Acad. Sci.
U.S.A. 107, 9055 (2010)].
