Half-metallic and magnetic properties of Mn₂Co_1-xNi_xSn (x = 0 – 1) Heusler alloys

Heusler alloys with half-metallic properties are in high demand for spintronic devices because they can generate fully spin-polarized currents. These compounds also display promising thermoelectric [1], optical and transport properties [2]. In this work, we present density functional theory (DFT) calculations of the electronic structure and magnetic properties of Mn₂Co_1-xNi_xSn (x = 0 – 1) Heusler alloys, which—apart from their parent compositions—have not yet been reported in the literature. These alloys crystallize in the XA-type (so-called inverse) Heusler structure with space group F–43m. For x=0, Mn₂CoSn is calculated to be a half-metal with a half-metallic gap of less than 1 eV for one of the spin projections, resulting in a spin polarization of 98% [3]. Our calculated electronic densities of states reveal that replacing the cobalt ions with nickel closes the band gap. This occurs because the electronic states that formed the half-metallic gap in Mn₂CoSn shift below the Fermi energy, while the peak in the opposite spin projection moves above the Fermi energy. Consequently, the spin polarization of the Mn₂Co_1-xNi_xSn alloys containing nickel is decreased. The total magnetic moment of Mn₂CoSn is 3 μ_B, which satisfies the Slater–Pauling rule. For the nickel-bearing compositions, the total magnetic moment varies from 1.8 to 0.7 μ_B. Thus, the investigated Mn₂Co_1-xNi_xSn compounds are promising functional materials whose spin polarization and magnetic moments can be tuned across a wide range of values by adjusting the composition. The results of this study were published in [3]. It was carried out within the framework of the state assignment of the Ministry of Science and Higher Education of the Russian Federation for IMP UrB RAS.