  Recent fabrication of atomic precision nanodevices for spintronics greatly
boosted their performance and also revealed new interesting features, as
oscillating magnetoresistance with number of atomic layers in a multilayered
structure. This motivates the need to go beyond the usual theoretical approach
of semi-classical continuous layers. Here the simple tight-binding dynamics is
used to describe quantum conduction in a multicomponent system with
spin-polarized electrodes separated by an ultrathin and atomically coherent
non-magnetic spacer (either metallic or insulating). A possibility is indicated
for obtaining a huge resonant enhancement of magnetoresistance in such device
by a special choice of gate voltage on the spacer element.
