  The isostructural alloying of two compounds with extremely different magnetic
and thermo-structural properties has resulted in a new system,
(MnNiSi)1-x(FeCoGe)x, that exhibits extraordinary magnetocaloric properties
with an acute sensitivity to applied hydrostatic pressure (P). Application of
hydrostatic pressure shifts the first-order phase transition to lower
temperature ($\Delta$ T=-41 K with P=3.43 kbar) but preserves the giant value
of isothermal entropy change (-$\Delta$S$\max$=143.7 J/kg K for a field change
of {\Delta}B=5 T at atmospheric pressure). Together with the magnetic field,
this pressure-induced temperature shift can be used to significantly increase
the effective relative cooling power.
