Optimum Annealing Conditions for the Magnetocaloric Effect in Mn-Fe-P-Ge Alloys

Mn-Fe based alloys are currently being used as magnetocaloric materials in near-room-temperature magnetic cooling applications. These alloys can exhibit a magneto-structural phase transition, leading to a giant magnetocaloric effect (MCE). The magnitude of the MCE is sensitive to annealing conditions, hence, the effect of annealing on the MCE was studied. The crystal structure and magnetocaloric properties of Mn
_1.1
Fe
_0.9
P
_0.75
Ge
_0.25
powder samples were determined for various annealing conditions. The MCE was significantly influenced by annealing. The optimum annealing temperature and time for maximum relative cooling power (~303 J kg
^-1
) were 1123 K and 9 h, respectively. The maximum magnetic entropy change (~25 J kg
^-1
K
^-1
) was obtained after annealing at 1223 K for 9 h, but this was accompanied by maximum thermal hysteresis.