Tuning spin filtering by anchoring groups in benzene derivative molecular junctions.

Abstract

One of important issues of molecular spintronics is the control and manipulation of charge transport and, in particular, its spin polarization in single molecule junctions. Using <i>ab</i> <i>initio</i> calculations, we explore spin-polarized electron transport across single benzene derivatives attached with six different anchoring groups (S, CH₃S, COOH, CNH₃NH, NC and NO₂) to Ni(111) 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 CNH₃NH 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 a valuable quantitative information for future experimental measurements on that kind of systems and will be useful for designing high-performance spintronics devices.