Spin transport in ferromagnetic/normal-metal tunnel junction arrays

An array of alternating ferromagnetic and normal-metal islands separated by small tunnel junctions is theoretically investigated in the sequential tunneling regime. A numerical Monte Carlo method is used to calculate the transport properties. The spin-dependent tunneling currents give rise to nonequilibrium spin accumulation on the normal island. The tunneling magneto resistance (TMR) is calculated for a large range of array parameters. The TMR oscillates with bias voltage and can become negative for certain array parameters. We show that the long-range electrostatic interaction in the arrays can significantly increase the TMR; for experimentally accessible parameters the magnitude of the TMR can be as large as 100%.