The Effects of Cotunneling and Spin Flip on the Spin Polarized Transport in a Ferromagnetic Single Electron Transistor

We present a theoretical study of spin polarized transport in a single-electron tunneling transistor with ferromagnetic source and drain electrodes. The sequential tunneling and cotunneling currents are analyzed as a function of the intrinsic spin polarization of the electrodes, and spin flip effects within the central island electrode, for the case of collinear magnetization configuration. It was found that an antiparallel alignment of the electrode magnetization leads to a suppression of both the sequential tunneling and cotunneling currents, with the degree of suppression being greater for the higher order cotunneling current. For the sequential case, the suppression can be reduced by introducing finite spin flip within the island, but this has virtually no effect on the cotunneling current.