  We investigate the structural, electronic and magnetic properties of the full
Heusler compounds Mn$_2$YSn (Y = Mo, Nb, Zr) by first-principles density
functional theory using the generalized gradient approximation. It is found
that the calculated lattice constants are in good agreement with the
theoretical values. We observe that the Cu$_2$MnAl-type structure is more
stable than the Hg$_2$CuTi type. The calculated total magnetic moments of
Mn$_2$NbSn and Mn$_2$ZrSn are 1 $\mu_{\text{B}}$ and 2 $\mu_{\text{B}}$ at the
equilibrium lattice constant of 6.18 \AA and 6.31 \AA, respectively, for the
Cu$_2$MnAl-type structure. Mn$_2$MoSn have a metallic character in both
Hg$_2$CuTi and Cu$_2$MnAl type structures. The total spin magnetic moment obeys
the Slater-Pauling rule. Half-metal exhibits 100% spin polarization at the
Fermi level. Thus, these alloys are promising magnetic candidates in spintronic
devices.
