  Giant magnetocaloric (GMC) materials constitute a requirement for near room
temperature magnetic refrigeration. (Fe,Mn)$_2$(P,Si) is a GMC compound with
strong magnetoelastic coupling. The main hindrance towards application of this
material is a comparably large temperature hysteresis, which can be reduced by
metal site substitution with a nonmagnetic element. However, the
(Fe,Mn)$_2$(P,Si) compound has two equally populated metal sites, the
tetrahedrally coordinated $3f$ and the pyramidally coordinated $3g$ sites. The
magnetic and magnetocaloric properties of such compounds are highly sensitive
to the site specific occupancy of the magnetic atoms. Here we have attempted to
study separately the effect of $3f$ and $3g$ site substitution with equal
amounts of vanadium. Using formation energy calculations, the site preference
of vanadium and its influence on the magnetic phase formation are described. A
large difference in the isothermal entropy change (as high as 44\%) with
substitution in the $3f$ and $3g$ sites is observed. The role of the lattice
parameter change with temperature and the strength of the magnetoelastic
coupling on the magnetic properties are highlighted.
