  We study theoretically the quantum size effects of a magnetic resonant
tunneling diode (RTD) with a (Zn,Mn)Se dilute magnetic semiconductor layer on
the spin-tunneling time and the spin polarization of the electrons. The results
show that the spin-tunneling times may oscillate and a great difference between
the tunneling time of the electrons with opposite spin directions can be
obtained depending on the system parameters. We also study the effect of
structural asymmetry which is related to the difference in the thickness of the
nonmagnetic layers. It is found that the structural asymmetry can greatly
affect the traversal time and the spin polarization of the electrons tunneling
through the magnetic RTD. The results indicate that, by choosing suitable
values for the thickness of the layers, one can design a high speed and perfect
spin-filter diode.
