Transition from minority to majority spin transport in iron-manganese nitride Fe4−xMnxN films with increasing x

Herein, 30 nm-thick Fe4−xMnxN (x = 0, 1, 2, 3, and 4) epitaxial films were grown on MgO(001) substrates by molecular beam epitaxy, and the anisotropic magnetoresistance (AMR) properties were measured at temperatures (T) between 10 and 300 K. A negative AMR effect was observed in the Fe4N and FeMn3N films at T ≤ 300 K and in the Mn4N film at T ≤ 100 K. In contrast, a positive AMR effect was observed in the Fe3MnN and Fe2Mn2N films at T ≤ 300 K. Using the relationship between the AMR ratio, the spin polarization of the density of states at the Fermi level, and the spin polarization of the electrical conductivity (Pσ), we derived the sign of Pσ to be negative in Fe4N, Fe3MnN, and Fe2Mn2N and to be positive in FeMn3N and Mn4N. These results show that the minority spin transport is dominant in Fe4−xMnxN for x = 0, 1, and 2 at lower temperatures, whereas the majority spin transport is dominant with increasing x in Fe4−xMnxN for x = 3 and 4.