Fe, Ni and Co nitrides with perovskite structures are conducting ferromagnets with high mechanical resistance, low coercitivity and large saturation moments, suitable for exploitation in magnetic and magnetoresistive devices. Promising applications in high density recording media and sensors require tailoring nanostructures from the parent bulk compound/alloy, with the largest possible unit cell magnetization. This depends on the combined effects of unit cell volume, local symmetry and T–Fe ions interaction that we investigate by spin-polarized all electron FPLMTO calculations. We simulate systematically bulk Fe3N unit cells with substitutional T atoms at FeI (corner) or FeII (face) site to ascertain the interplay of T-Fe (electronic), T-N ( volumic) and T-Fe-N (volumic and electronic) interactions. The magnetic moments per atom and f.u. are calculated at i) three values of the experimental lattice parameter (in a.u.) a0= 7.1715 , a1=7.1753 , a2=7.1621 , and ii) for different XC-approximations. The conditions that in Fe4N lead to the formation of saturated (corner) and unsaturated (face) moments are found also in the alloys considered here. This twofold behaviour is less pronounced in CoFe3N but striking in MnFe3 where also spin flip of the Mn moments occurs. MnFe3N is the only compound where Mn substitution of Fe induces a quite dramatic decrease of the other Fe moments
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