  The spin transfer effect in ferromagnet-quantum dot (insulator)-ferromagnet
Aharonov-Bohm (AB) ring system with Rashba spin-orbit (SO) interactions is
investigated by means of Keldysh nonequilibrium Green function method. It is
found that both the magnitude and direction of the spin transfer torque (STT)
acting on the right ferromagnet electrode can be effectively controlled by
changing the magnetic flux threading the AB ring or the gate voltage on the
quantum dot. The STT can be greatly augmented by matching a proper magnetic
flux and an SO interaction at a cost of low electrical current. The STT,
electrical current, and spin current are uncovered to oscillate with the
magnetic flux. The present results are expected to be useful for information
storage in nanospintronics.
