Tuning Magnetocaloric Effect of a Mn-Cr-Sb-Ga alloy by the Nonvolatile Residual Strain of a Ti-Ni Shape Memory Alloy

The multiferroic composites with a layer of magnetocaloric materials (MCMs) on a piezoelectric substrate have recently been developed to tune the magnetocaloric effect (MCE) through the stress from the piezoelectric substrate, which could help achieve high-efficiency and miniaturized refrigeration. The small strain of piezoelectric substrates is sufficient to tune the MCE of alloys whose transformation temperature (T_M) is sensitive to the external stress. However, it might not work effectively for those stress-insensitive MCMs, which are also important MCMs with considerable MCE and small hysteresis. In this paper, we design a new composite with a Mn_1.95Cr_0.05Sb_0.95Ga_0.05 ribbon on a Ti₅₀Ni₅₀ shape-memory-alloy substrate. The Ti₅₀Ni₅₀ substrate can provide much larger nonvolatile stress than a piezoelectric substrate, which thus successfully tunes the MCE of the Mn_1.95Cr_0.05Sb_0.95Ga_0.05, despite its low stress sensitivity. With a 2% residual strain of the Ti₅₀Ni₅₀ substrate, T_M of the Mn_1.95Cr_0.05Sb_0.95Ga_0.05 is increased by ~6 K, which ~7.5 times that (0.8 K) achieved via a Mn_1.95Cr_0.05Sb_0.95Ga_0.05/PMN-PT composite. With different residual strains of Ti₅₀Ni₅₀ substrate from 0% to 2%, a wide working temperature window of 31 K is obtained at a low magnetic field of 1 T. Moreover, this composite exhibits an almost constant refrigeration capacity and a small hysteresis of 4.9 K under different stress, which promotes homogeneous heat transfer and improves the working efficiency. This work provides an effective method to tune the MCE of both stress-sensitive and stress-insensitive MCMs, which could be used in miniaturized refrigerators.