Spin polarized transport of iron nitride Fe4N:: Analysis using a combination of first principles calculation and model calculation

To propose a ferromagnet exhibiting a highly spin-polarized transport, we analyze the spin polarization ratio of the bulk Fe4N (Curie temperature: 761 K), which is focused on by taking into account the fact that a ferromagnetic electrode containing Fe and a light element enhances the tunnel magnetoresistance effect at room temperature. The spin polarization ratio is here defined by P = (sigma up arrow-sigma down arrow)/(sigma up arrow+sigma down arrow) with sigma up arrow(sigma down arrow) being the conductivity at zero temperature of up spin (down spin). The conductivity is obtained using the Kubo formula and the Slater-Koster tight binding model, where parameters are determined by fitting the band structure of the model to that of the first principles calculation. In the vicinity of the Fermi energy, vertical bar P vertical bar takes almost 1.0, which is 5.0 times as large as that of bcc-Fe. It may suggest that Fe4N is very effective as a spin injection electrode. Also, by comparing Fe4N to fcc-Fe in the ferromagnetic state with the equilibrium lattice constant of Fe4N, it is shown that N plays an important role in increasing vertical bar P vertical bar. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.