Multi-phase transition behavior over a wide temperature range in magnetocaloric (Mn, Fe, Ni)2(P, Si) alloys

This study investigates the magnetocaloric property of MnFe0.95-xNixP0.6Si0.4 (x = 0.02, 0.03, 0.04) alloys over a wide temperature range and their related phase transitions. These P-rich composition alloys, with a P/Si ratio of 1.5, exhibit multi-phase transition behavior across a broad temperature range. In-situ 2D X-ray diffraction reveals overlapping diffraction peaks of the Fe2P-type hexagonal structure throughout the ferromagnetic-paramagnetic transition, rather than a single, drastic transition. This observation suggests the formation of a multi-phase structure within the alloys. Consequently, these alloys exhibit high refrigeration capacity (RC) values ranging from 168.6 to 218.1 J kg(-1) under an applied magnetic field of 2 T. Notably, these RC values are superior to those observed in other P/Si ratio compositions without multi-phase transitions or even Gd, a representative magnetocaloric material. This improved performance demonstrates the promising potential of these multi-phase transition alloys as candidates for magnetocaloric refrigeration systems.