Non-equilibrium spin accumulation in ferromagnetic single-electron transistors

We study transport in ferromagnetic single-electron transistors. The non-eq uilibrium spin accumulation on the island caused by a finite current throug h the system is described by a generalized theory of the Coulomb blockade. It enhances the tunnel magnetoresistance and has a drastic effect on the ti me-dependent transport properties. A transient decay of the spin accumulati on may reverse the electric current on time scales of the order of the spin -flip relaxation time. This can be used as an experimental signature of the non-equilibrium spin accumulation.