  Recent conductance measurements on multi-wall carbon nanotubes (CNTs) reveal
an effective behavior similar to disordered single-wall CNTs. This is due to
the fact that electric current flows essentially through the outermost shell
and is strongly influenced by inhomogeneous electrostatic potential coming from
the inner tubes. Here, we present theoretical studies of spin-dependent
transport through disorder-free double-wall CNTs as well as single-wall CNTs
with Anderson-type disorder. The CNTs are end-contacted to ferromagnetic
electrodes modelled as fcc (111) surfaces. Our results shed additional light on
the giant magnetoresistance effect in CNTs. Some reported results concern
realistically long CNTs, up to several hundred nanometers.
