Highly conductive and complete spin filtering of nickel atomic contacts in a nitrogen atmosphere

Generating efficient and highly spin-polarized currents through nanoscale junctions is essential in the field of nanoelectronics and spintronics. In this paper, using $ab$ $initio$ electron transport calculations, we predict highly conductive and perfect spin filtering of nickel atomic contacts in a nitrogen environment, where a single N$_2$ molecule sits in parallel (energetically most favorable) between two nickel electrodes. Such a particular performance is due to the wave function orthogonality between majority spin $s$-like states of ferromagnetic electrodes and the lowest unoccupied molecular orbital of the N$_2$ molecule, and thus, majority spin electrons are completely blocked at the interface. For the minority spin, on the contrary, two almost saturated conducting channels were formed due to the effective coupling between $d_{zx,zy}$ of the Ni atom and $p_{x,y}$ of the N atom, resulting in large conductance of about 1$G_0$ ($=2e^2/h$). As a consequence, a single N$_2$ molecule acts as a highly conductive and half-metallic conductor. On the other hand, the CO and NO incorporated molecular junctions exhibit rather low conductance with a partially spin-polarized current.