Spin-polarized electron transport through nanometer-scale Al grains

We investigate spin-polarized electron tunneling through ensembles of nanometer-scale Al grains embedded between two Co reservoirs at 4.2 K, and observe tunneling-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 the Al grains and asymmetric electron dwell times.