  With a goal to produce giant magnetic moment in Mn$_{13}$ cluster which will
be useful for practical applications, we have considered the structure and
magnetic properties of pure Mn$_{13}$ cluster and substitutionally doped it
with X = Ti, V, Cr, Fe, Co, Ni atom to produce Mn$_{12}$X clusters. We find
that Ti and V substitutions in Mn$_{13}$ cluster are the most promising in
terms of gaining substantial binding energy as well as achieving higher
magnetic moment through ferromagnetic alignment of atom-centered magnetic
moments. This has been demonstrated in terms of energetics and electronic
properties of the clusters. For comparison, we have also studied the effect of
N-capping of Mn$_{13}$ cluster, predicted in the earlier work [Phys. Rev. Lett.
{\bf 89}, 185504 (2002)] as a means to produce stable giant magnetic moment in
Mn clusters upto cluster size of 5 Mn atoms.
