Spin effects in single-electron tunneling in magnetic junctions

Spin-dependent single-electron tunneling in ferromagnetic double junctions is analyzed theoretically in the limit of sequential tunneling. It is shown that spin accumulation on the central electrode gives rise to tunnel magnetoresistance due to rotation of the external electrode magnetizations from antiparallel to parallel alignment, even when the central electrode is nonmagnetic. The influence of discrete energy spectrum of the central electrode on spin accumulation, spin fluctuations and tunnel magnetoresistance is also analyzed.