Band-structure calculations of the half-metallic ferromagnetism and structural stability of full- and half-Heusler phases

Self-consistent first principle calculations within the local density approximation were used to study the effect of lattice distortions on the electronic and magnetic properties of half (NiMnSb) and full-Heusler (Co₂CrAl) compounds. We find that NiMnSb is half-metallic from -2% to $+3%$ uniform strain, whereas Co₂CrAl is half-metallic from -1% to $+3%$. The loss of the half-metallic character is primarily due to a shift in the density of states relative to the Fermi energy. Under tetragonal distortions, high spin polarization at the Fermi level is maintained over a larger range, but the gap width is strongly affected. Therefore, only nonuniform strain should not be the expected reason for the poor performance of Heusler compounds in spintronic devices. The impacts of these results on spintronic devices are discussed.