  We propose a ferromagnetic spintronic system, which consists of two serial
connected resonant tunneling diodes. One diode is nonmagnetic whereas the other
comprises a ferromagnetic emitter and quantum well. Using a selfconsistent
coherent transport model we show that the current-voltage characteristic of the
ferromagnetic diode can be strongly modulated by changing the relative
orientation of the magnetizations in the emitter and quantum well,
respectively. By a continuous change of the relative magnetization angle the
total resistance exhibits a discrete jump realizing digital magneto resistance.
The interplay between the emitter's Fermi energy level and the relative
magnetization orientations allows to tailor the current voltage characteristics
of the ferromagnetic diode from ohmic to negative differential resistance
regime at low voltages.
