  We study theoretically the spin-dependent transport in
ferromagnet/normal-metal/ferromagnet double tunnel junctions by special
attention to cotunneling in the Coulomb blockade region. The spin accumulation
caused by cotunneling squeezes the Coulomb blockade region when the
magnetizations in the ferromagnetic electrodes are antiparallel. Outside the
squeezed Coulomb blockade region, we propose a new anomalous region, where the
sequential tunneling in one of the spin bands is suppressed by the Coulomb
blockade and that in the other is not. In this region, the tunnel
magnetoresistance oscillates as a function of bias voltage. The temperature
dependences of the tunnel magnetoresistance and the magnitude of the spin
accumulation are calculated.
