Outstanding caloric performances for energy-efficient multicaloric cooling in a Ni-Mn-based multifunctional alloy

Magnetic shape memory alloys (MSMAs) have attracted great interests due to their multifunctional properties associated with external-field-induced martensitic transition, such as magnetostrain, magnetoresistance, magnetocaloric effect and elastocaloric effect. Search for MSMAs displaying a unique combination of strong metamagnetic transition and stable, large caloric effect is nowadays very active. Here we report the simultaneous achievement of a strong metamagnetic transition as well as a large magnetic-field-induced entropy change of 17.4 J kg⁻¹ K⁻¹ under 2 T and a stable, large elastocaloric effect with adiabatic temperature change of ∼5.0 K during more than 2100 mechanical cycles, in a Ni-Fe-Co-Mn-Sn MSMA. Such combination in a single material has never been reported in the literature. Furthermore, we demonstrate that fully reversible metamagnetic transition and consequently large, reversible multicaloric effect can be achieved by increasing magnetic field from 0 T to 2 T at zero stress and decreasing field from 2 T to 0 T at a uniaxial stress of 23.5 MPa. This dual-stimulus magnetic-mechanical multicaloric cooling cycle also provides an opportunity for achieving reversible magnetoresistance and magnetostrain under the coupling of a low magnetic field and small stress, which is beneficial for practical applications. The high cyclic stability of large caloric effects is ascribed to the good geometric compatibility at the interface between austenite and martensite as revealed by employing multiscale characterization approaches, including in-situ synchrotron high-energy X-ray diffraction and transmission electron microscopy. This study has great implications on developing high-performance multifunctional alloys with magnetostructural transition for actuation, magnetic recording and solid-state refrigeration applications.