We explore the electronic structures of transition-metal-based chalcopyrites $TM{X}_2$ ($X=\mathrm{S}$, Se, and Te) to establish a concept of half-metallic antiferromagnets (HM-AFM’s) within the class of tetrahedrally coordinated ternary systems. Using a full-potential muffin-tin approach and the spin-polarized density functional method, we find two series of HM-AFM’s: $\mathrm{CrFe}{X}_2$ and $\mathrm{VCo}{X}_2$, where two constituent magnetic ions in a unit cell have antialigned local moments that cancel exactly by virtue of the integer filling of one spin channel. The bonding nature is interpreted in terms of the “ghost-bond-orbital model”; the $T$-$X$ bonds are covalent while the $M$-$X$ bonds are ionic, suggesting the magnetic interaction in each bond is due to ferromagnetic double exchange and antiferromagnetic superexchange, respectively, in the conventional scheme.

• Received 9 August 2006

DOI:https://doi.org/10.1103/PhysRevB.74.172404