Interplay of spin accumulation and Coulomb blockade in double ferromagnetic junctions

Single-electron tunneling in a double junction in which a nonmagnetic metallic island is separated from two ferromagnetic electrodes by tunnel barriers, is analysed theoretically in the sequential tunneling regime and for an arbitrary intrinsic spin relaxation time on the island. It is shown that nonequilibrium spin polarization of the island results in tunnel magnetoresistance due to rotation of the electrode magnetizations from antiparallel to parallel alignment. It is also shown that discrete charging of the island gives rise to a fine structure in the voltage dependence of the island spin polarization and tunnel magnetoresistance