Spin-dependent resonant tunneling based spin valves and spin-current sources

We describe a principle for designing double-barrier magnetic tunneling str uctures that could produce a spin current with controllable spin direction or have an optimal spin valve effect. The principle is based on the finding that, by tuning the energy positions of the spin-dependent resonant tunnel ing of a double-barrier junction, a fully spin-polarized current and optima l magnetoresistance could be achieved. This is illustrated by numerical cal culations within a 3-dimensional effective single-electron model of the spi n-dependent currents in several tunneling structures.