Enhancement of Magnetocaloric Properties by Magnetoelastic Coupling Behavior

In magnetic cooling devices, which are promising alternatives to conventional gas compression cooling systems, the selection of appropriate magnetocaloric materials as coolant is a critical factor. Since the initial demonstration of magnetic cooling using gadolinium (Gd), extensive research has been conducted to find suitable substitutes for rare earth Gd to facilitate the commercialization of magnetic cooling technology.<br/> (Mn, Fe)₂(P, Si) alloys, known for their excellent magnetocaloric property, are among the most promising alternative materials for magnetic cooling device. In this work, we investigated the control of characteristic temperature, operating temperature range and cycle stability of these alloys through compositional adjustments. Lattice variation within the hexagonal structure, induced by temperature variations, were observed to cause magnetic phase transition of these alloys, and this phenomenon is called <i>magnetoelastic coupling</i>. Specifically, it was observed that Ni doping at the Fe site shifts the lattice variation temperature causes a characteristic temperature shift near room temperature with a notable magnetic entropy change value of over 15 J/kg K at 2 T. Additionally, compositions with a P/Si ratio exceeding 1.5 exhibited multi-phase Fe₂P-type hexagonal structures and complex lattice changes, leading to <i>table-like</i> magnetic entropy change curves and an extended operating temperature range, thereby enhancing the refrigeration capacity of these alloys. Finally, we confirmed that variations in the lattice change width, influenced by P/B control of non-metallic elements, affect the cycle stability of these alloys, as verified using our custom measurement system. <br/>In this presentation, changes in the <i>magnetoelastic coupling</i> behavior of (Mn, Fe, Ni)₂(P, Si) alloys that occur through a compositional approach and the correlation between the resulting changes in properties and coolant utilization will be discussed in detail.