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Tetragonally ordered Fe2Ni2N powder was successfully synthesized from L10-FeNi using a nitrogen topotactic reaction. The magnetic properties and structural stability of the tetragonally ordered Fe2Ni2N were examined using first principles calculations. The nitriding process gives 96 wt% of tetragonally ordered Fe2Ni2N phase and the rest is the more nitrided phase of FeNiN. Analysis of the crystal structure confirmed that the c/a is 0.989 for the tetragonally ordered Fe2Ni2N, which is consistent with the results of the first-principles calculations. Magnetization measurements reveal that the Curie temperature and thermal decomposition temperatures are 441 and 667 K, respectively. The high field magnetization processes at 10 K indicate that the sample contains a component of high magnetic anisotropy energy Ku. The Ku estimated by the law of approach to ferromagnetic saturation is 1.51 MJ/m3, which is in reasonably good agreement with that obtained by the first-principles calculations 1.96 MJ/m3.

MgO-barrier magnetic tunnel junctions with half-metallic Heusler alloy electrodes have attracted considerable attention for spintronics applications. However, there remain a couple of issues related to materials that should be resolved before practical use. Recently, quarterly equiatomic Heusler alloys have attracted attention as advanced Heusler alloys. CoIrMnZ (Z = Al, Si, Ga, and Ge) half-metallic Heusler alloys were designed and predicted to have moderate Curie temperatures and to be lattice-matched with the MgO barrier, which is advantageous compared to traditional Co2 Heusler alloys T. T [T. Roy et al., J. Magn. Magn. Mater. 498 (2020) 166092]. Here, we experimentally investigated the structure and magnetic properties of thin films composed of one of these alloys, CoIrMnAl, fabricated by sputtering deposition. We successfully obtained films with the B2 chemical ordering, even without a post-annealing process. The lattice constants for the films annealed at 500–600 ∘C were approximately equal to the predicted values. The magnetization at 10 K was close to 500 kA/m, and the Curie temperature was approximately 400 K, which were approximately 70% of the values predicted for the fully ordered structure. The magnetic properties observed in the B2-ordered films were well explained by ferrimagnetism that appeared in the B2-ordered CoIrMnAl with full-swap disorders of Co-Ir and Mn-Al and almost full-swap disorder of Co-Mn, which was predicted from the first-principles calculations.

Using first principles calculations based on density functional theory, we study electronic and magnetic properties of CoIrMnZ (Z = Al, Si, Ga, Ge) Heusler systems. Based on the electronic structure calculations, CoIrMnSi and CoIrMnGe are predicted to be half-metallic. For the studied systems, the ground state magnetic configurations are found to be ferromagnetic with magnetic moment consistent with the Slater-Pauling rule. The calculated ferromagnetic transition temperatures are much higher than the room temperature for all the cases. The effect of spin orbit coupling has been discussed on the electronic structure for all the systems studied here. Furthermore, we construct junctions with MgO along (001) direction. The MnZ terminations are found to be energetically more favourable compared to the CoIr terminations. After discussing the tunnelling conductance, we find that CoIrMnSi/MgO/CoIrMnSi could be a promising magnetic tunnelling junction (MTJ) candidate.

A powder sample of body-centered tetragonal Ni2N in a single phase was prepared by a high rate-type triode dc reactive sputtering and the magnetic properties have been reinvestigated. It is confirmed that Ni2N is not a ferromagnet. However, the material is not a simple paramagnet either and shows a weak spin-glass-like behavior at low temperatures with a freezing temperature of about 8 K. Posible origins of the behavior are discussed. Band-structure calculations are reported to see the stability of the nonmagnetic ground state of bct Ni2N against lattice expansion and appearance of nitrogen vacancies.