  The volume expanding magnetostructural transition in Mn$_3$GaC and Mn$_3$SnC
has been identified to be due to distortion of Mn$_6$C octahedra. Despite a
similar lattice volume as Mn$_3$SnC and similar valence electron contribution
to the density of states as in Mn$_3$GaC, Mn$_3$InC does not undergo a first
order magnetostructural transformation like the Ga and Sn antiperovskite
counterparts. A systematic investigation of its structure and magnetic
properties using probes like x-ray diffraction, magnetization measurements,
neutron diffraction and extended x-ray absorption fine structure (EXAFS) reveal
that though the octahedra are distorted resulting in long and short Mn -- Mn
bonds and different magnetic moments on Mn atoms, the interaction between them
remains ferromagnetic. This has been attributed to the strain on the Mn$_6$C
octahedra produced due to the relatively larger size of In atom compared to Sn
and Ga. The size of In atom constricts the deformation of Mn$_6$C octahedra
giving rise to Mn -- Mn distances that favor only ferromagnetic interactions in
the compound.
