First-principles investigation of spin polarized conductance in atomic carbon wire

TL;DR

This study uses first-principles calculations to explore spin-dependent conductance in atomic carbon wires with magnetic cobalt terminals, revealing spin-valve behavior and the influence of wire length on magnetic and conductive properties.

Contribution

It provides a detailed analysis of spin-dependent energetics and conductance in atomic carbon wires, highlighting the effects of wire length and structure on magnetic configurations and conductance.

Findings

Anti-parallel Co spins are stable in shorter wires due to super-exchange.

Conductance exhibits spin-valve behavior with higher values for parallel spins.

Conductance varies non-monotonically with wire length for both spin states.

Abstract

We analyze spin-dependent energetics and conductance for one dimensional (1D) atomic carbon wires consisting of terminal magnetic (Co) and interior nonmagnetic (C) atoms sandwiched between gold electrodes, obtained employing first-principles gradient corrected density functional theory and Landauer's formalism for conductance. Wires containing an even number of interior carbon atoms are found to be acetylenic with sigma-pi bonding patterns, while cumulene structures are seen in wires containing odd number of interior carbon atoms, as a result of strong pi-conjugation. Ground states of carbon wires containing up to 13 C atoms are found to have anti-parallel spin configurations of the two terminal Co atoms, while the 14 C wire has a parallel Co spin configuration in the ground state. The stability of the anti-ferromagnetic state in the wires is ascribed to a super-exchange effect. For the cumulenic wires this effect is constant for all wire lengths. For the acetylenic wires, the super-exchange effect diminishes as the wire length increases, going to zero for the atomic wire containing 14 carbon atoms. Conductance calculations at the zero bias limit show spin-valve behavior, with the parallel Co spin configuration state giving higher conductance than the corresponding anti-parallel state, and a non-monotonic variation of conductance with the length of the wires for both spin configurations.