Electronic transport in iron atomic contacts: from the infinite wire to realistic geometries

TL;DR

This paper theoretically investigates spin-polarized electronic transport in iron atomic contacts, comparing ideal infinite wires with realistic geometries, and explores how defects and contacts influence transmission and magnetoresistance properties.

Contribution

It introduces a self-consistent tight-binding model for spin-polarized transport in Fe contacts, analyzing effects of defects, contacts, and spin-orbit coupling on transmission and magnetoresistance.

Findings

Transmission of d electrons is more affected by defects than s electrons.

Contact effects can suppress certain transmission channels.

Magnetoresistance behavior varies from step-like to smooth with defects.

Abstract

We present a theoretical study of spin polarized transport in Fe atomic contacts using a self-consistent tight-binding Hamiltonian in a non-orthogonal $s$, $p$ and $d$ basis set, the spin-polarization being obtained from a non-collinear Stoner-like model and the transmission probability from the Fisher-Lee formula. The behaviour of an infinite perfect Fe wire is compared with that of an infinite chain presenting geometric defects or magnetic walls and with that of a finite chain connected to infinite one-dimensional or three-dimensional leads. In the presence of defects or contacts the transmission probability of $d$ electrons is much more affected than that of $s$ electrons, in particular, contact effects may suppress some transmission channels. It is shown that the behaviour of an infinite wire is never obtained even in the limit of long chains connected to electrodes. The introduction of the spin-orbit coupling term in the Hamiltonian enables us to calculate the anisotropy of the magneto-resistance. Finally whereas the variation of the magneto-resistance as a function of the magnetization direction is step-like for an infinite wire, it becomes smooth in the presence of defects or contacts.