First-principle prediction of half-metallic ferrimagnetism of the Heusler alloys Mn2CoZ (Z = Al, Ga, Si, Ge) with a high-ordered structure

Using the first-principles plane-wave pseudopotential method within the generalized gradient approximation framework based on density functional theory, we have investigated the electronic structure and magnetism of the Heusler alloys Mn2CoZ (Z = Al, Ga, Si, Ge) with a high-ordered structure which is similar to the L21 structure of the full-Heusler compounds but with different sequence of atoms in the unit cell. It was shown that the high-ordered structural Mn2CoZ alloys are all ideal half-metallic ferrimagnets at their respective equilibrium lattice constant. They have a total magnetic moment of 2.0 μB for Mn2CoAl (Ga) and 3.0 μB for Mn2CoSi (Ge) per unit cell, respectively. The results are in good agreement with the Slater–Pauling rule. We also found that these alloys maintain half-metallicity within a wide range of lattice constants between 5.4 and 5.9 Å.