  We analyse the effects of doping Holmium impurities into the full-Heusler
ferromagnetic alloy Co$_2$MnSi. Experimental results, as well as theoretical
calculations within Density Functional Theory in the "Local Density
Approximation plus Hubbard U" framework show that the holmium moment is aligned
antiparallely to that of the transition metal atoms. According to the
electronic structure calculations, substituting Ho on Co sites introduces a
finite density of states in the minority spin gap, while substitution on the Mn
sites preserves the half-metallic character.
