Spin-dependent single electron tunneling in double tunnel junctions with a nano-granular layer

We have examined the spin-dependent tunneling properties of ferromagnetic double tunnel junctions with a nanogranular ferromagnetic intermediate layer, whose average grain size is about 2 nm. At low temperatures, samples show a linear current - voltage characteristic at low voltages, which indicate elastic coherent tunneling. In this regime, the conductances for both parallel and anti-parallel configurations of the magnetizations of the grains fluctuate to the applied bias voltage, with spin-dependent periods. The tunnel magnetoresistance ratio can be as large as 100%. We can conclude that we have observed a spin-dependent single electron tunneling via a single discrete level for the first time in a metallic system. (C) 2003 Elsevier B. V. All rights reserved.