Spin-polarized transport properties of GdN nanocontacts

Gadolinium nitride (GdN) nanocontacts were recently experimentally shown to be efficient spin filters. Our study is aimed at identifying and analyzing the physical processes responsible for the high spin polarization of the tunneling current in GdN nanostructures. By the example of planar contacts and atomic chains attached to Cu electrodes we assert, using first principle techniques, that a 100% spin-filtering effect can be indeed achieved in GdN nanocontacts. Our analysis shows that the spin filtering is due to the predominant role of nitrogen majority $p$ states in the electron transport, while minority conductance decays exponentially with contact size due to the presence of a minority band gap at the Fermi level. Additionally, GdN zigzag infinite chains are found to be as efficient spin filters as their planar contact counterparts, also exhibiting a 100% spin-filtering effect, which is robust against chain geometry changes.

Figure 1

(a) Sketch of the studied system—a Cu/GdN/Cu planar nanocontact. (b) Top view of the last Cu layer and the first GdN layer at the Cu/GdN interface. Black frames denote one unit cell, used for calculation.

Figure 2

Majority (blue triangles) and minority (red squares) zero-bias conductance of a Cu/GdN/Cu tunneling junction at the Fermi level (logarithmic scale) and the resulting polarization of conductance (green circles) as a function of GdN-layer thickness.

Figure 3

Spin resolved projected density of states of N-$p_x,p_y,p_z$ (a) and Gd-$d_{xy},d_{xz},d_{yz}$ (b) states for an infinitely thick slab of GdN epitaxially sandwiched between Cu electrodes (stretched in the $xy$ plane by 5% and allowed to relax along the $z$ direction; see text for discussion). Shaded areas present the corresponding DOS of an ideal GdN bulk.

Figure 4

Symmetry decomposed PDOS of the interface Cu (a), Gd (b). and N (c) atoms of a Cu/GdN/Cu junction with 19 GdN layers. Shaded areas in (b) and (c) represent the Gd-$d_{\text{tot}}$ and N-$p_{\text{tot}}$ PDOS of the central layer of the junction, which is nigh-identical to bulk GdN. Layer resolved Fermi level PDOS of Gd-$d_{z^2}$ and N-$p_z$ states is shown in (d) and (e), respectively.

Figure 5

Energy and equilibrium parameter $h$ (a), spin resolved zero-bias conductance (b), and spin polarization of conductance (c) of a planar GdN chain (sketch on the right) as a function of the chain stretching parameter $d$.

Figure 6

Projected density of states (top panels: N-$p$; middle: Gd-$s,p,d$) and zero-bias transmission coefficients (bottom panels) of infinite Gd-N chain at stretching parameters $d$ of $3.8$ (a), $4.0$ (b), and $4.3\AA$ (c).