  To date, endeavors in nanoscale spintronics are dominated by the use of
single-electron or single-spin transistors having at their heart a
semiconductor, metallic or molecular quantum dot who's localized states are
non-spin-degenerate and can be controlled by an external bias applied via a
gate electrode. Adjusting the bias of the gate one can realign those states
with respect to the chemical potentials of the leads and thus tailor the
spin-polarized transmission properties of the device. Here we show that similar
functionality can be achieved in a purely metallic junction comprised of a
metallic magnetic chains attached to metallic paramagnetic leads and biased by
a gate electrode. Our ab initio calculations of electron transport through
mixed Pt-Fe (Fe-Pd and Fe-Rh) atomic chains suspended between Pt (Pd and Rh)
electrodes show that spin-polarized confined states of the chain can be shifted
by the gate bias causing a change in the relative contributions of majority and
minority channels to the nano-contact's conductance. As a result, we observe
strong dependence of conductance spin-polarization on the applied gate
potential. In some cases the spin-polarization of conductance can even be
reversed in sign upon gate potential application, which is a remarkable and
promising trait for spintronic applications.
