  Coherent spin-dependent electronic transport is investigated in a molecular
junction made of polymeric chain attached to ferromagnetic electrodes (Ni and
Co, respectively). Molecular system is described by a simple Huckel model,
while the coupling to the electrodes is treated through the use of a broad-band
theory. The current flowing through the device is calculated within
non-equilibrium Green's function approach. It is shown that tunnel
magnetoresistance of molecular junction can be quite large (over 100 %)and
strongly depends on: (i) the lenght of the polymeric chain and (ii) the
strength of the molecule-to-electrodes coupling.
