Spin-polarized tunnel current in magnetic-layer systems and its relation to the interlayer exchange interaction

The spin-polarized tunnel current and its connection to the interlayer exch ange interaction is studied in ferromagnet-insulator-ferromagnet thin-film planar junctions out of equilibrium. Building on the nonequilibrium Keldysh formalism, it is possible to systematically include a contact interaction between localized spins and conduction electrons and extend previous treatm ents on spin currents and exchange interaction. In particular, a Landauer-t ype formula is derived for the spin current that explains the result found earlier [Schwabe, Wingreen, and Elliott, Phys. Rev. B 54, 12 953 (1996)] th at the exchange interaction between the ferromagnetic slabs increases in pr oportion to the slab width. Furthermore, switching is shown to occur betwee n parallel and antiparallel coupling of the slabs for different applied bia ses under feasible experimental conditions. [S0163-1829(99)08705-6].