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Theoretical analysis of transport in ferromagnetic single-electron transistors in the sequential tunneling regime

Wiśniewska J., Weymann I.

Materials Science Poland

2008

Vol. 26, No. 3

716--722

Spin-dependent transport properties of a single-electron transistor have been analysed, whose two external electrodes and the central part (island) are ferromagnetic. Based on the real-time diagrammatic technique, all transport contributions have been calculated up to the first order in the coupling strength between the island and the leads – this comprises a sequential tunnelling. Relevant occupation probabilities of different charge states are determined from the generalized master equation in the Liouville space. Assuming that spin relaxation processes on the island are sufficiently fast to neglect spin accumulation, we analyze electric current flowing through the system in the parallel and antiparallel magnetic configurations, as well as the resulting tunnel magnetoresistance. We show that transport characteristics of ferromagnetic single-electron transistors exhibit a strong dependence on the magnetic configuration of the system. Furthermore, we also demonstrate that the bias dependence of both the differential conductance and tunnel magnetoresistance displays an oscillatory-like behaviour resulting from single-electron charging effects.

Transport characteristics of ferromagnetic single-electron transistors with non-collinear magnetizations

Wiśniewska J., Kowalik M., Barnaś J.

Materials Science Poland

2006

Vol. 24, No. 3

761--767

Theoretical analysis of spin-polarized transport through a ferromagnetic single-electron transistor (FM SET) has been carried out in the sequential tunneling regime. Two external electrodes and the central part (island) of the device are assumed to be ferromagnetic, with the corresponding magnetizations being generally non-collinear. Transport properties of the FM SET are analyzed within the master equation approach, with the respective transition rates determined from the Fermi golden rule. It is assumed that spin relaxation processes on the island are sufficiently fast to neglect spin accumulation. It is shown that electric current and tunnel magnetoresistance (TMR) strongly depend on magnetic configuration of the device. Transport characteristics of symmetrical and asymmetrical structures have been calculated as a function of bias and the gate voltages.