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

Abstract

We present a theoretical study of spin polarized transport in Fe atomic contacts by using a self-consistent tight-binding Hamiltonian in a nonorthogonal $s$, $p$, and $d$ basis set, the spin polarization being obtained from a noncollinear Stoner-like model and the transmission probability from the Fisher--Lee formula. The behavior of an infinite perfect Fe wire is compared to that of an infinite chain presenting geometric defects or magnetic walls and to 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 behavior 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 magnetoresistance. Finally, whereas the variation in the magnetoresistance as a function of the magnetization direction is steplike for an infinite wire, it becomes smooth in the presence of defects or contacts.