A theoretical analysis on highly spin-polarized transport of iron nitride Fe_4N

TL;DR

This paper provides a theoretical analysis demonstrating that bulk Fe4N exhibits nearly perfect spin-polarized transport, with the nitrogen atom playing a key role in enhancing this property, which is promising for spintronic applications.

Contribution

The study introduces a theoretical framework showing that Fe4N has near-perfect spin polarization, highlighting the importance of nitrogen in achieving this property.

Findings

|P| approaches 1 near the Fermi energy, indicating nearly perfect spin polarization.

Nitrogen atom significantly enhances spin polarization compared to pure fcc-Fe.

Theoretical analysis uses Kubo formula and tight binding model fitted to first-principles data.

Abstract

In order to propose a ferromagnet exhibiting highly spin-polarized transport, we theoretically analyzed the spin polarization ratio of the conductivity of the bulk Fe$_4$N with a perovskite type structure, in which N is located at the body center position of fcc-Fe. The spin polarization ratio is defined by $P = (\sigma_\uparrow - \sigma_\downarrow) / (\sigma_\uparrow + \sigma_\downarrow )$, with $\sigma_{\uparrow(\downarrow)}$ being the conductivity at zero temperature of the up spin (down spin). The conductivity is obtained by using the Kubo formula and the Slater-Koster tight binding model, where parameters are determined from the least-square fitting of the dispersion curves by the tight binding model to those by the first principles calculation. In the vicinity of the Fermi energy, $|P|$ takes almost 1.0, indicating perfectly spin-polarized transport. In addition, by comparing Fe$_4$N to fcc-Fe (Fe$_4$N$_0$) in the ferromagnetic state with the equilibrium lattice constant of Fe$_4$N, it is shown that the non-magnetic atom N plays an important role in increasing $|P|$.