Spin-dependent transport in ferromagnetic single-electron transistors with non-collinear magnetizations

Electronic transport in a ferromagnetic single-electron transistor is analysed theoretically in the sequential tunnelling regime. One of the external electrodes and the central part (island) of the device are assumed to be ferromagnetic, with the corresponding magnetizations being non-collinear. The analysis is based on the master equation method, and the respective transition rates are determined from the Fermi golden rule. It is shown that the electric current and corresponding tunnel magnetoresistance (TMR) strongly depend on the angle between the magnetizations. For an arbitrary magnetic configuration, TMR is modulated by charging effects, which give rise to characteristic dips (cusps) at the bias voltages corresponding to the Coulomb steps in the current-voltage characteristics.