High-Performance Spin Filters Based on 1,2,4,5-Tetrahydroxybenzene Molecules Attached to Bulk Nickel Electrodes

Achieving highly spin-polarized current at the nanoscale is of paramount importance in molecular spintronics. Using a self-consistent ab initio approach that combines the nonequilibrium Green’s function formalism with spin density functional theory, we explore the spin transport properties of a set of 1,2,4,5-tetrahydroxybenzene (THB)-based molecular junctions with nickel electrodes. Our calculations show that the junction incorporating a dehydrogenated THB molecule exhibits remarkable spin-filtering effects as well as a high transmission for the spin-down (minority) electrons around the Fermi level. This is due to the favorable alignment of the frontier molecular orbitals relative to the electrode Fermi level and the orthogonality between these π-symmetry molecular states and the 4s conducting channels of the nickel electrodes. In addition, the Ni–O bonds at the molecule-electrode interfaces are very robust. The spin-filtering efficiency can be further improved by introducing one more THB molecule and a central nickel atom into the tunneling path. Finally, the adsorption of CO over the central nickel atom significantly promotes the transport of spin-down electrons and reduces that of spin-up (majority) electrons, achieving a nearly 100% spin polarization at finite bias voltages. Our findings demonstrate great potential of these classes of THB-based junctions for future high-performance molecular spintronic devices.