  We report ab initio calculations of spin-dependent transport in single atomic
carbon chains bridging two zigzag graphene nanoribbon electrodes. Our
calculations show that carbon atomic chains coupled to graphene electrodes are
perfect spin-filters with almost 100 % spin polarization. Moreover, carbon
atomic chains can also show a very large bias-dependent magnetoresistance up to
1000000 % as perfect spin-valves. These two spin-related properties are
independent on the length of carbon chains. Our report, the spin-filter and
spin-valve are conserved in a single device simultaneously, opens a new way to
the application of all-carbon composite spintronics.
