First-principle prediction of half-metallic ferrimagnetism of the Heusler alloys Mn2CoZ (ZÂ =Â 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.