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Effective exchange interaction in tunnelling junctions based on a quantum dot with non-collinear magnetic moments of the leads

100%

Rudziński W.

tom Vol. 22, No. 4

523--528

Electron tunnelling through a spin-split discrete level of an interacting quantum dot coupled to two ferromagnetic electrodes (leads) is investigated theoretically in the sequential-tunnelling regime. Spinsplitting of the dot level is induced by an effective exchange interaction between the spin on the dot and spins in the leads. The calculations apply to arbitrary angles enclosed between the magnetizations of the external electrodes. It is shown that the interplay between effective exchange field and Coulomb correlations on the dot may enhance the tunnel magnetoresistance at certain bias voltages. It is also found that a large spin splitting appearing for strong Coulomb correlations gives rise to an enhanced diode-like effect. Finally, it is shown that by rotating the magnetization of one of the electrodes, one can modulate the amplitude of the spin-polarized current, from a blockade in the parallel or antiparallel configuration to its maximum value in the non-collinear case.

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

100%

Wiśniewska J. , Weymann I. , Barnaś J.

tom Vol. 22, No. 4

461--467

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.

Torque due to spin-polarized current in ferromagnetic single-electron transistors

88%

Kowalik M. , Wiśniewska J. , Barnaś J.

Materials Science Poland

2006

tom Vol. 24, No. 3

815--820

Theoretical analysis of the current-induced torque acting on magnetic moment of the central part (island) of a ferromagnetic single-electron transistor has been carried out in the regime of sequential tunneling. The island is assumed to be ferromagnetic and attached to two leads (electrodes). One of the leads is ferromagnetic, and the corresponding magnetic moment is oriented arbitrarily. The torque is calculated from the spin current absorbed by the magnetic moment of the island, and the calculations are carried out in the limit of fast spin relaxation on the island (no spin accumulation).

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

75%

Wiśniewska J. , Kowalik M. , Barnaś J.

Materials Science Poland

2006

tom 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.