First-principles investigation of Heusler alloys M₂CoA(M=Mn, Ti; A=Al, Si)

The electronic structure and magnetic properties of the M₂CoA type Heusler alloys Mn₂CoAl, Mn₂CoSi, Ti₂CoAl and Ti₂CoSi were systematically investigated using first-principles calculations based on the density functional theory. The results show that Mn₂CoAl is a ferrimagnetic spin gapless semiconductor; Mn₂CoSi and Ti₂CoAl are ferrimagnetic spin half-metals, while Ti₂CoSi is a ferromagnetic spin half-metal. The total spin magnetic moments of the M₂CoA type Heusler alloys are integers, obeying the Slater-Pauling rule. By analyzing the band structures and electronic density of states, the origin of spin gapless semiconductor as well as half-metal were revealed. The calculation results of phonon dispersion curves and elastic constants show that all the M₂CoA type Heusler alloys are stable in the lattice dynamics and mechanics.