Spin-Polarized Electron Transport through Nanometer-Scale Al Grains

Abstract

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 the Hanle effect. The spin-coherence time ($T_2^\star$), measured from the Hanle effect, is $\sim ns$. Fast dephasing is attributed to electron spin-precession in the local fringing fields. Dephasing does not destroy $TMR$, in contrast to spin-relaxation. $TMR$ is strongly asymmetric with bias voltage, which we explain by spin-relaxation. The voltage dependence of $TMR$ is not simple and it is explained by a rapid decrease of the spin-relaxation time with bias voltage. This suggests that spin-relaxation in Al grains is concurrent with electronic relaxation, analogous to that in bulk.