  Half-metallic ferrimagnetism is crucial for spintronic applications with
respect to ferromagnets due to the lower stray fields created by these
materials. Studying the effect of defects in CrAs and related transition-metal
chalcogenides and pnictides crystallizing in the zinc-blende structure, we
reveal that the excess of the transition-metal atoms leads to half-metallic
ferrimagnetism. The surplus of these atoms are antiferromagnetically coupled to
the transition-metal atoms sitting at the perfect lattice sites. The needed
condition to achieve half-metallic ferrimagnetism is to prevent the migration
of the $sp$ atoms to other sites and the atomic swaps.
