Enhanced Magnetocaloric Properties of Annealed Melt-Extracted Mn_1.3Fe_0.6P_0.5Si_0.5 Microwires

The highly regarded Fe₂P-based magnetocaloric materials are usually fabricated by ball milling, and require an additional extended annealing treatment at high temperatures (at temperatures up to 1423 K for several hours to days). In this work, we show that fabricating Mn_1.3Fe_0.6P_0.5Si_0.5 into the form of microwires attained 82.1 wt.% of the desired Fe₂P phase in the as-cast state. The microwires show a variable solidification structure along the radial direction; close to the copper wheel contact, Fe₂P phase is in fine grains, followed by dendritic Fe₂P grains and finally secondary (Mn,Fe)₅Si₃ phase in addition to the dendritic Fe₂P grains. The as-cast microwires undergo a ferro- to para-magnetic transition with a Curie temperature of 138 K, showing a maximum isothermal magnetic entropy change of 4.6 J kg⁻¹ K⁻¹ for a magnetic field change of 5 T. With further annealing, a two-fold increase in the maximum isothermal magnetic entropy change is found in the annealed microwires, which reveal 88.1 wt.% of Fe₂P phase.