Gate control of spin-polarized conductance in alloyed transitional metal nanocontacts

Abstract

To date, endeavors in nanoscale spintronics are dominated by the use of single-electron or singlespin 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. INTRODUCTIONAs spintronics evolves from a holy grail of science and technology into an everyday phenomenon, its foundations demand for the same cornerstones as conventional spindegenerate electronics is built on: miniaturization, robustness and tunability. Technological progress nowadays has enabled both scientists and engineers to build nanometer and sub-nanometer-scale devices not only with elaborate and volatile break junction, 1-4 electromigration 5 or STM extraction 6 techniques, but also with virtually integration-ready nanotube/nanowire and lithography based technologies.7-12 Robustness of transport properties is usually achieved by a combination of single-electron and coulomb-blockade physics 7,13-16 with strong magnetic properties guaranteed by the use of magnetic materials with high spin moment 7,17 and geometry/topology based stability of the latter.18-20 The tunability, or the susceptibility of spin-dependent transport properties 21,22 to external perturbations can be achieved in several ways. Orientation and ordering of spins in magnetic systems can be "programmed" into atomic-scale junctions at construction stage (e.g., by tuning the chemical composition and geometry of the device 4,7,[17][18][19][23][24][25] ), but it is even more important and challenging to be able to dynamically and reversibly tune those properties after the junction has been completed or integrated into a circuit. The "traditional" way of controlling transmission properties of both conventional and single-electron transistors is the field effect, i.e. external bias application by means of an additional gate electrode. Gate bias in a three-terminal device can be used to control both paramagnetic transport 2,26,27 and magnetic...