The half-metallicity and magnetism at the (001) surface of half-Heusler-structured YCrSb and YMnSb were investigated using the all-electron full-potential linearized augmented plane wave method within the generalized
gradient approximation. Both YSb-terminated surfaces and Cr- or Mn-terminated surfaces were considered for YCrSb and YMnSb. From the calculated local density of states and the total magnetic moments of the
systems, the half-metallicity of the YSb-terminated (001) surface for YCrSb was preserved, whereas the surface for YMnSb was almost half-metallic. In contrast, the half-metallicity was destroyed at the Cr- or Mn-terminated surface of YCrSb or YMnSb. The magnetic moments of the Cr and Mn atom at the (001) surface were increased by 28 % and 15 %, respectively, compared to the bulk values due to band narrowing and increased exchange splitting at the surface.