Ferromagnetism-dependent polytypism: CrAs versus MnAs

Density spin-polarized functional theory using pseudopotential plane wave method is used here to explore the structural and magnetic properties of 3C, 4H, 6H and 2H polytypes of transition metal arsenides: CrAs and MnAs. The results reveal that CrAs manifest weak dependence of the lattice parameter a and the c/a ratio versus hexagonality, but for MnAs, the lattice parameters display strong dependence on crystal polytype. Most importantly, our results show that the different crystal 3C, 4H, 6H and 2H polytypes exhibit significant distinct magnetism in CrAs and MnAs. While the total spin moments induced in CrAs is strongly independent of the crystal structure adopted, the ferromagnetism in MnAs is found sensitive to polytypism.