  We theoretically investigate magnetoresistance (MR) effects in connection
with spin filtering in quantum-coherent transport through tunnel junctions
based on non-magnetic/semimagnetic heterostructures. We find that spin
filtering in conjunction with the suppression/enhancement of the spin-dependent
Fermi seas in semimagnetic contacts gives rise to (i) spin-split kinks in the
MR of single barriers and (ii) a robust beating pattern in the MR of double
barriers with a semimagnetic well. We believe these are unique signatures for
quantum filtering.
