Low-pressure-induced giant barocaloric effect in an all-d-metal Heusler Ni35.5Co14.5Mn35Ti15 magnetic shape memory alloy

The clean and energy-efficient solid-state refrigeration based on magnetostructural phase transformation is a promising alternative technology for vapor-compression refrigeration. Herein, using a unique quasi-direct calorimetric method in a high hydrostatic pressure condition, we have studied the barocaloric effect for a Ni35.5Co14.5Mn35Ti15 all-d-metal Heusler alloy that undergoes a martensitic transformation accompanied by a large magnetization change. The martensitic transformation is found to be sensitive to either applied pressure or magnetic field with the large transformation temperature driving rates of 5.8 K kbar(-1) and 2.0 K T-1. Such a sensitive response to external stimuli originates from the large lattice/volume- and magnetization-discontinuity on the phase transformation. The Ni35.5Co14.5Mn35Ti15 alloy exhibits a large barocaloric effect with an isothermal entropy change of -24.2 J kg(-1) K(-1)and an adiabatic temperature change of 4.2 K, concomitant with a relatively low pressure change of 1 kbar, appearing to be the largest values among those of reported magnetic shape memory alloys. Moreover, by virtue of the strong magnetostructural coupling in the Ni35.5Co14.5Mn35Ti15 alloy, we propose a strategy of applying/releasing pressure and magnetic field in a proper sequence to eliminate the hysteresis and effectively enhance the reproducibility of the barocaloric effect.