First-Principles Study of Magnetic and Half-Metallic Properties of Mn2Co1–xNixSn Alloys with Spin Polarization

Many Heusler alloys are half-metals because of the band structure with one of the spin projections insulating and another one being metallic that provides a possibility for 100% spin-polarized current. We present the first-principles calculations of the electronic structure and magnetic properties of M-n2Co1‒xNixSn Heusler alloys for x = 0–1. The alloys crystallize in the XA-type Heusler structure. For x = 0, Mn2CoSn is found to be a half-metal with a band gap of less than 1 eV in the majority spin direction, thus the spin-polarization of current is almost full. The other compositions are found to be metallic in the density of states with spin polarization near 0.3. The presence of Ni in Mn2Co1–xNixSn Heusler alloys results in the band gap shift to the lower energies. In Mn2CoSn, the total magnetic moment equal to 3 µB satisfies the Slater–Pauling rule. With the increasing nickel concentration, the total magnetic moment decreases, however, the magnetic moment of all Mn ions become large. The Mn–Co–Ni-based alloys are promising for spintronic applications due to the high spin polarization and composition-dependent total magnetic moment.