Spin-Resolved Transport Properties of a Pyridine-Linked Single Molecule Embedded between Zigzag-Edged Graphene Nanoribbon Electrodes

We study the spin-dependent electron transport through a junction consisting of a single pyridine-linked (PDL) molecule sandwiched between two zigzag-edged graphene nanoribbon (ZGNR) electrodes modulated by an external magnetic field, where 4,4′-bipyridine, 4,4′-vinylenedipyridine, and 4,4′-ethylenedipyridine molecules are considered, respectively. By using ab initio calculations based on the density functional theory combined with nonequilibrium Green’s function formalism, it is shown that the spin-charge transport can be modulated by performing different magnetic configuration in the ZGNR electrodes. Specifically, we demonstrate that the proposed PDL molecular junctions exhibit several interesting effects, including (dual) spin-filtering, rectifying, negative differential resistance (NDR), and magnetoresistance. For the junction consisting of a 4,4′-bipyridine molecule with proper magnetic configuration in the two ZGNRs, it is interesting to note that a perfect spin polarization with filtering efficiency up to 100% can be found, the maximum value of rectification ratio can reach up to 104, and the peak to valley ratio of NDR reach up to 328, respectively. Furthermore, the magnetoresistance ratio for this junction can also go up to 106%. Besides, the physical mechanisms for those phenomenons are revealed. The mechanisms are revealed and analyzed by the connection of these effects to the evolution of the frontier molecular orbital, the spin-resolved transmission spectrum associated with the local density of states around the Fermi level at zero bias, and the molecular projected self-consistent Hamiltonian.