We discuss quasi-two-dimensional (2D) half-metallic (HM) antiferromagnets (AFMs), or fully compensated half-metallic ferrimagnets, that have no spontaneous magnetization, yet have 100% spin polarization of their conduction electrons. Using a full-potential augmented plane-wave method within density functional theory, we see that the substitution of Cr ions for half of the Fe ions in Fe-based superconductors such as LaFeAsO, SrFeAsF, and $\alpha$-FeSe leads to 2D HM-AFM conduction. With stiff spacer layers such as LaO and SrF, the CrFeAs${}_2$ layers show HM-AFM behavior in both striped and checkerboard phases, whereas the spacer-free CrFeSe${}_2$ layers become semimetallic in the striped phase, being degraded by orthorhombic distortion. The checkerboard phase is energetically favored over the striped phase. Despite the absence of inversion symmetry in the checkerboard phase, spin-orbit coupling of spin-polarized conduction electrons shows little effect on the half-metallicity.

• Received 2 February 2011

DOI:https://doi.org/10.1103/PhysRevB.83.214404