  We investigated the electronic and magnetic properties of a series of
zinc-blend II-V compounds by carrying out density-functional-theory
calculations including spin-orbit couplings. Contrary to the case of CaN and
CaP, the half-metallic characteristics of the II-V compounds such as CaSb and
CaBi were found to be destroyed. Our analysis of the valence band structures of
CaAs, CaSb, and CaBi revealed a critical role of the spin-orbit coupling
interactions on the exchange-split band structure, thereby leading to breakdown
of the half-metallic ferromagnetism for the systems with heavier group V
elements in the zinc-blend II-V compounds.
