Transport characteristics of ferromagnetic single-electron transistors

Spin-dependent electronic transport in a single-electron transistor with ferromagnetic external electrodes and ferromagnetic or nonmagnetic central part (island) is analyzed theoretically in the sequential tunneling regime. Nonequilibrium magnetic polarization of the island due to spin accumulation (spin-dependent chemical potential) is taken into account. The accumulation takes place when the spin relaxation time on the island is sufficiently long. The crossover from slow to fast spin relaxation limits is also analyzed. The tunnel magnetoresistance, magnetic polarization of the island, and spin polarization of the flowing current are examined as a function of the bias and gate voltages.