Size effect of spin-polarized transport in FM/Single-walled carbon nanotube/FM junctions

► For short carbon nanotubes there is a strong size effect of spin-polarized transport in FM/SWCNT/FM junctions. ► The effect of tunnel magnetoresistance (TMR) in zigzag tube is stronger than that in armchair tubes. ► For all zigzag tubes when the size exceeds a limit TMR reaches one maximum 20% and the size effect disappears. ► For zigzag tubes TMR value can be negative at some special sizes and the extremum is at the angle π. ► For all armchair tubes, TMR has two extrema: the maximum at π/2 and the minimum at π.