Spin-coherent quantum transport in carbon nanotube magnetic tunnel junctions is investigated theoretically. A spin-valve effect is found for metallic, armchair tubes, with a magnetoconductance ratio ranging up to $20\%$. Because of the finite length of the nanotube junctions, transport is dominated by resonant transmission. The magnetic tunnel junctions are found to have distinctly different transport behavior depending on whether or not the length of the tubes is commensurate with a $3N+1$ rule, with $N$ the number of basic carbon repeat units along the nanotube length.

• Received 29 October 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.2682