Large plateau-like Magnetic entropy change in Sn doped Ni-Co-Mn-Ti all d metal Heusler alloy

Abstract

In recent years, magnetic refrigeration (MR) has gained much attention, rather than conventional gas refrigeration, being an energy efficient and eco-friendly technology. For that purpose, the current research for exploring potential magnetocaloric material is focused on the material exhibiting first-order magnetostructural transition (MST) along with large change in magnetization and hence large magnetocaloric effect (MCE) [1]–[3]. Recently, Ni-Co-Mn-Ti-based all d-metal Heusler alloy is found to be an excellent candidate for magnetic refrigeration which exhibits multicaloric properties such as MCE [4], elastocaloric effect [5], and giant barocaloric effect [6].In the present work, we explore the effect of Sn doping at Ti-site and also heat treatment condition on MCE properties of Ni35Co15Mn37Ti13-xSnx (x = 0,1 and 2) alloys through thermal and magnetic measurements. The observed MST temperature (TM) shifts toward lower temperature with Sn doping whereas, the sharpness of the transition enhances with annealing time which effectively increases the MCE response as shown in fig.1 (a)). The sample with x = 1 exhibits a plateau-like magnetic entropy change (ΔSM) with a maximum peak value of ΔSM ~ 5.7 Jkg-1K-1 due to a magnetic field change of 50 kOe. It is interesting to note that ΔSM value remains almost the same with value ~ 4 Jkg-1K-1 for a temperature region of 300 K-350 K shown in fig.1 (b). Large ΔSM in a wide temperature interval is attributed to the existence of inter-martensite transition along with MST. The large ΔSM value with wide tunable operating temperature region in the vicinity of room temperature and the estimated large relative cooling power (RCP) of ~ 384 J/kg enable the material a suitable candidate for solid-state MR technology.  Figure 1: (a) Magnetization vs. T for x = 1 and 2alloys under different annealing temperatures. Inset shows DSC heat-flow vs. T with a ramp rate of 10 K/m of x = 1 sample.  Figure 1: (b) ΔSM vs. T at different magnetic field for x = 1 alloy.