Tuning spin filtering by anchoring groups in benzene derivative molecular junctions

Abstract

One of the important issues of molecular spintronics is the control and manipulation of charge transport and, in particular, its spin polarization through single-molecule junctions. Using ab initio calculations, we explore spin-polarized electron transport across single benzene derivatives attached with six different anchoring groups (S, CH3S, COOH, CNH2NH, NC and NO2) to Ni(1 1 1) electrodes. We find that molecule-electrode coupling, conductance and spin polarization (SP) of electric current can be modified significantly by anchoring groups. In particular, a high spin polarization (SP > 80%) and a giant magnetoresistance (MR > 140%) can be achieved for NO2 terminations and, more interestingly, SP can be further enhanced (up to 90%) by a small voltage. The S and CH3S systems, on the contrary, exhibit rather low SP while intermediate values are found for COOH and CNH2NH groups. The results are analyzed in detail and explained by orbital symmetry arguments, hybridization and spatial localization of frontier molecular orbitals. We hope that our comparative and systematic studies will provide valuable quantitative information for future experimental measurements on that kind of systems and will be useful for designing high-performance spintronics devices.