Stability of half-metallic ferromagnetism of zinc-blende type CrAs and MnM (M = Si, Ge and Sn)

By the first-principles calculations both for electronic structures and effective exchange constants, we investigate the stability of ferromagnetism of zinc-blende (ZB) type CrAs, and further examine a possibility of ferromagnetism of ZB type MnM (M = Si, Ge and Sri). ZB type CrAs, a half-metallic ferromagnet reported by Akinaga's group [Jpn. J. Appl. Phys. 39 (2000) L1118], is found to have an effective exchange constant (J(0) = Sigma(inot equal0)J(i0)) larger than 150meV above the lattice constant of GaAs (a = 5.65 Angstrom), showing quite stable ferromagnetism above room temperature as was observed experimentally. We predict that ZB type MnM (M = Ge, Si, Sn) whose valence electron numbers are the same as that of CrAs also exhibit half-metallic ferromagnetism having a positive J(0) large enough at a = 5.82 Angstrom, indicating that the Curie temperatures are higher at least than room temperature.