Theoretical analysis of highly spin-polarized transport in the iron nitride Fe4 N

In order to propose a ferromagnet exhibiting highly spin-polarized transport, we theoretically analyzed the spin polarization ratio of the conductivity of the bulk Fe4 N with a perovskite-type structure, in which N is located at the body center position of the fcc-Fe. The spin polarization ratio is defined by P= (σ↑ - σ↓) (σ↑ + σ↓), with σ↑ (↓) 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 a perfectly spin-polarized transport. In addition, by comparing Fe4 N to fcc-Fe (Fe4 N0) in the ferromagnetic state with the equilibrium lattice constant of Fe4 N, it is shown that the nonmagnetic atom N plays an important role in increasing P.