First-principles study of properties of semi-Heusler (Cu,Ni)MnSb alloys

Magnetic properties, Curie temperatures, and transport properties of semi-Heusler alloys CuxNi1-xMnSb are calculated as a function of the alloy composition from first-principles. The transition from the ferromagnetic state (NiMnSb) to the antiferromagnetic state (CuMnSb) gives rise to an abrupt change in the concentration dependence of magnetic moments and resistivity at about x = 0.7 while the Curie temperatures decrease monotonically with the Cu-content. Such behaviour can be understood as due to the onset of disorder in orientations of Mn-spins at x = 0.7. A simple account of magnetic disorder as based on the uncompensated disordered local moment picture provides also a good quantitative explanation of available experimental data.