Single- and double-island ferromagnetic single-electron transistors

Electronic transport in a ferromagnetic single-electron transistor has been considered theoretically in the sequential tunneling regime. The device consists of two external leads and one or two islands as the central part, connected to the leads by tunneling barriers. External gates are additionally attached to the islands. Generally, the two external electrodes and the islands can be ferromagnetic with arbitrary orientation of the corresponding magnetic moments. We have carried out detailed theoretical analysis of the current-voltage characteristics and spin-valve magnetoresistance in the limit of fast spin relaxation on the islands. Asymmetry in tunneling probabilities of spin-majority and spin-minority electrons leads to interesting features in the transport characteristics, like for instance magnetoresistance oscillations with the bias and gate voltages, negative differential resistance, and others.