  The structural, electronic, and magnetic properties of half-Heusler alloys
CKMg and SiKMg are studied by using first-principle density functional theory.
The calculations reveal the SiKMg alloy is a half-metallic ferromagnet with the
magnetic moment of 1 $\mu_B$ per formula unit at equilibrium lattice constant.
The magnetic moment mainly originates from the strong spin-polarization of $p$
electrons of Si atom and partial involvement of $d$ electrons of K atom. The
half-metallic gap is 0.105 eV. The robustness of half-metallic against the
lattice constants for SiKMg is also calculated. CKMg alloy is nearly
half-metallic with a spin polarization of 99.99 \%\ at equilibrium lattice
constant, but it is a good half-metallic alloy when a low pressure is applied.
This shows CKMg is a very promising spintronic functional material.
