  Structural, magnetic and magnetocaloric properties of Fe2P-based Mn-Fe-P-Si
compounds were investigated. The study reveals a large magneto-elastic coupling
that starts to develop in the paramagnetic state and grows when the
ferromagnetic transition temperature is approached. Based on the behavior of
the magneto-elastic coupling, we show the thermal evolution of the magnetic
moments. On cooling, magnetic moments on the tetrahedral site form and
gradually increase in the paramagnetic state. At the magnetic ordering
temperature the moments attain a much larger value in a discontinuous step. We
also find that the hysteresis and magnetic entropy change are correlated with
discontinuous changes in the lattice parameters at the transition temperature.
Small hysteresis can be obtained while maintaining giant magnetocaloric effect.
