On the giant magnetocaloric and mechanical properties of Mn–Fe–P–Si-Ge alloy

We report the magnetocaloric properties of Mn1.15Fe0.85P0.65Si0.13Ge0.2B0.02 alloy prepared by mechanical alloying followed by spark plasma sintering and annealing the spark plasma sintered alloy. The X-ray diffraction pattern confirms the presence of hexagonal Fe2P-type phase in both (as-prepared and annealed) alloys. Annealing of the spark plasma sintered alloy leads to the increase of the volume fraction of the Fe2P phase from 87% to 98% and a decrease in the lattice volume. Thermo-magnetic measurements show that Curie temperature (TC) decreases from 291 K to 289 K after annealing the spark plasma sintered alloy. Thermal hysteresis reduces from 19 K to 9 K after annealing the spark plasma sintered alloy. The magnetic entropy evaluated from magnetization measurements was found to be 8 J/kg-K in the spark plasma sintered alloy and it increases to 19 J/kg-K in the annealed spark plasma sintered alloy under 3 T magnetic field. The refrigerant capacity of the annealed spark plasma sintered alloy was found to be 200 J/kg at 3 T. The adiabatic temperature change of the annealed alloy has been estimated from the heat capacity measurements and it was found to be 1.9 K at 1 T and increases to around 2.7 K under a magnetic field of 3 T. Annealing the spark plasma sintered alloy leads to decrease in the hardness and it is observed that both the alloys crack after thermal cycling. However, the large change in magnetic entropy and adiabatic temperature change very near to the room temperature makes Mn1.15Fe0.85P0.65Si0.13Ge0.2B0.02 alloy a promising magnetocaloric material.