  We investigate spin-polarized electron tunnelling through ensembles of
nanometer scale Al grains embedded between two Co-reservoirs at 4.2K, and
observe tunnelling-magnetoresistance (TMR) and effects from spin-precession in
the perpendicular applied magnetic field (the Hanle effect). The spin-coherence
time ($T_2^\star$) measured using the Hanle effect is of order $ns$. The
dephasing is attributed to electron spin-precession in local magnetic fields.
Dephasing process does not destroy $TMR$, which is strongly asymmetric with
bias voltage. The asymmetric TMR is explained by spin relaxation in Al grains
and asymmetric electron dwell times.
