Sequential tunneling and shot noise in ferromagnet/normal-metal/ferromagnet double tunnel junctions

The tunneling through a ferromagnet/normal metal/ferromagnet double junction in the Coulomb blockade regime is studied, assuming that the spin relaxation time of electron in the central metallic island is sufficiently large. Using the master equation, the current, the tunnel magnetoresistance (TMR), and the current noise spectrum have been calculated for devices of different parameters. It was shown that the interplay between spin and charge correlations strongly depends on the asymmetry of measured device. The charge correlation makes both the chemical potential shift, which describes the spin accumulation in the central island, and the TMR oscillated with the same period as the Coulomb staircase in current-voltage characteristics. This effect is smeared by the temperature. The spin correlation may cause an enhancement of noise at finite frequencies, while the zero frequency noise is still always sub-poissonian. The gate voltage causes an oscillation of not only conductance, but also TMR and noise.