Tailoring the conventional magnetocaloric effect via strain in a NiCuMnGa/TiZrNbFe bilayer composite near room temperature

Bilayer composites combining magnetocaloric alloys with shapeable substrates represent a typical approach to tuning the magnetocaloric effect (MCE) via substrate-induced stress, thereby facilitating high-efficiency and miniaturized refrigeration. However, conventional approaches utilizing Ti-Ni shape memory alloys as substrates are unable to sustain stable, nonvolatile strain near room temperature (RT), limiting their practical utility in tuning MCE. This study introduces a Ni_49.3Cu_7.5Mn_17.5Ga_25.7/Ti₇₀Zr_19.5Nb₁₀Fe_0.5 bilayer composite, in which the NiCuMnGa layer exhibits a significant entropy change of 9.35 J·K⁻¹·kg⁻¹ under a low magnetic field of 1 T near RT, and the TiZrNbFe substrate is capable of generating substantial nonvolatile residual strain (ε_r,sub) of up to 3.2% at temperatures below 505 K. By applying an ε_r,sub of 1.75%, the transition temperature and the effective working temperature window (ΔT_ETW) of the NiCuMnGa layer increase by 5.9 K. Furthermore, employing a series of composites with a ε_r,sub gradient ranging from 0% to 1.75% enables a 60% expansion in the ΔT_ETW of an active magnetic regenerator compared to the stress-free state. This work provides an effective method for stress-assisted MCE tuning, which could be used in miniaturized refrigerators.