Study of the transport properties of cobalt atomic contact under mechanical strain in a nitrogen atmosphere.

Achieving an efficient spin-filter effect and large magneto-resistance in molecular junctions is very important in spintronics. By employing the non-equilibrium Green's function formalism combined with the density functional theory, this study investigated the atomic structures and spin-resolved transport properties of molecular junctions consisting of nitrogen (N 2) sandwiched between two cobalt (Co) electrodes with different crystal lattices as a function of stretching distance. In the case of face-centred cubic Co electrodes, our calculations showed that the transport properties depend strongly on the stretching process, which changes the contact between the N 2 and Co electrodes. Specifically, the maximum spin polarization is due to the configuration of N 2 molecules sitting in parallel with the protruding Co atoms. Furthermore, the Co d xz,yz orbitals interact with the N p x,y orbitals, which contribute to the high transmission coefficient at the Fermi level for spin-down electrons. Meanwhile, the Co s-d z 2 hybridization orbitals, which interact weakly with the N p orbitals, contribute to the small transmission coefficient at the Fermi level. This can also be verified by the molecular junction model adopting simple monatomic Co chain electrodes, which also show a perfect spin-filter effect and achieve an ideal magnetoresistance. In contrast, in the case of hexagonal Co electrodes, the spin-filter effect disappears. However, the effect appears again by adding one more Co atom to the central point contact. Our findings show that the spin-resolved electronic transport of molecular junctions depends on the stretching process and the nature of the electrodes, which can help in the future design of molecular devices based on the spin degree of freedom. • The variation of atomic contact structures responds to the mechanical strain in the adiabatic approximation. • The spin-resolved transport properties depend on the stretching process and the nature of electrodes. • A perfect spin-filter device with ideal magneto-resistance is designed using N 2 sandwiched between monatomic Co chain. • The interaction between N p x,y and Co d xz,yz is Recognized and Verified in terms of the monatomic chain electrode model. • Developing a strategy turns the spin-filter effect. [ABSTRACT FROM AUTHOR]