New insights into the crystal structure and physical properties of the antiferromagnetic Mn₂MAl (M = Fe, Co, Ni) alloys

We present the theoretical and experimental results for the full Heusler alloys Mn₂MAl for late 3d transition metals – M = Fe, Co, Ni. For the first time, the synthesized Mn₂CoAl and Mn₂NiAl alloys crystallize in the β-Mn- and B2-types crystal structure. The electronic structure and magnetic properties of the alloys were investigated within the framework of first-principles theoretical calculations. It was revealed that the alloys have metallic properties and antiparallel alignment of the large Mn magnetic moments and almost compensated total magnetic moments. In addition, we investigated the effect of electronic correlations on the electronic structure and magnetic properties of the alloys within DFT + U method that resulted in a negligible effect for the total magnetic moments of Mn₂MAl (M = Fe, Co, Ni). The frequency dependence of the real and imaginary parts of the dielectric constant is measured in the spectrum region of 0.1–5 eV. In order to characterize thermoelectric properties of the studied Heusler alloys, we performed measurements of electrical resistivity and calculated Seebeck coefficient. The results are interpreted based on our theoretical calculations and different structural compositions.