Oscillatory spin-polarized conductance in carbon atom wires

Zero temperature spin-polarized transport in atomic wires consisting of magnetic (Co) and nonmagnetic (C) atoms sandwiched between gold electrodes is investigated using gradient-corrected density functional theory and Landauer's formalism. Our calculation shows a spin valve behavior with the parallel magnetization state between the two Co atoms giving higher conductance than the respective antiparallel magnetization state and a nonmonotonic variation of magnetoconductance with wire length. We term the more conductive parallel magnetization state the on state and the antiparallel magnetization state the off state. The ground state of wires containing up to five carbon atoms has antiparallel (off) spin configurations between the Co. The additional stability of the antiferromagnetic state in wires containing an even number of carbon atoms is ascribed to an enhanced superexchange mechanism facilitated by sigma-pi-conjugation present in the systems.