Enhanced local homogeneity obtained by induction melting for optimizing reversible magnetocaloric response in all-d-metal Ni(Co)-Mn-Ti Heusler alloys

All-d-metal Ni(Co)-Mn-Ti Heusler alloys showing giant magnetocaloric properties at near room temperature are highly desirable for solid-state cooling applications. However, when exploring the literature, the reported magnetocaloric properties vary widely, hinting at the importance of the synthesis route. In this work, we select the Ni 36 Co 14 Mn 35 Ti 15 composition, and systematically explore different synthesis routes such as arc melting, suction casting and induction melting, to investigate their effect on the magnetostructural transition and magnetocaloric properties. Among the studied samples, the induction melted sample shows the most abrupt martensitic transformation and the lowest thermal hysteresis: 4 K versus 8 K for arc melted and 17 K for suction casted. This abruptness leads to a remarkable isothermal entropy change of 23 J kg -1 K -1 for 1.5 T, along with the largest reversible response to date of 29 J kg -1 K -1 for 5 T, as compared to the reported magnetocaloric materials undergoing magnetostructural transition. The quantitative analysis of the elemental maps for the studied alloy series reveals that the larger homogeneity in the Ti distribution achieved by induction melting, when compared to the arc melted and suction casted counterparts, should be responsible for the sharpness of phase transformation and the low thermal hysteresis observed. The all-d-metal Ni 36 Co 14 Mn 35 Ti 15 Heusler alloy synthesized by induction melting stands out as the most impressive. It shows a uniform local distribution of Ti throughout the sample with the least deviation, which is responsible for the sharpness of the transition, and therefore the largest reversible magnetocaloric response (29 J kg -1 K -1 for 5 T) with minimal hysteresis. • Induction melting improves performance of all-d Heusler alloy • This is due to more homogeneous distribution of Ti throughout the matrix • Thermal hysteresis below 4 K is achieved • The largest reversible magnetocaloric response of magnetostructural transformations