  Cubic Half-Heusler Cu$_{1-x}$Co$_x$MnSb (0 $\leq$ $x$ $\leq$ 0.1) compounds
have been investigated both experimentally and theoretically for their
magnetic, transport and electronic properties in search of possible half
metallic antiferromagnetism. The systems (Cu,Co)MnSb are of particular interest
as the end member alloys CuMnSb and CoMnSb are semi metallic (SM)
antiferromagnetic (AFM) and half metallic (HM) ferromagnetic (FM),
respectively. Clearly, Co-doping at the Cu-site of CuMnSb introduces changes in
the carrier concentration at the Fermi level that may lead to half-metallic
ground state but there remains a persistent controversy whether the AFM to FM
transition occurs simultaneously. Our experimental results reveal that the AFM
to FM magnetic transition occurs through a percolation mechanism where
Co-substitution gradually suppresses the AFM phase and forces FM polarization
around every dopant cobalt. As a result a mixed magnetic phase is realized
within this composition range while a nearly HM band structure is developed
already at the 10% Co-doping. Absence of T$^2$ dependence in the resistivity
variation at low T-region serves as an indirect proof of opening up an energy
gap at the Fermi surface in one of the spin channels. This is further
corroborated by the ab-initio electronic structure calculations that suggests a
nearly ferromagnetic half-metallic ground state is stabilized by Sb-p holes
produced upon Co doping.
