Synergistic regulation of barocaloric and magnetocaloric effects in Ni₂MnGa: a quantitative phase field study

The central challenge in achieving efficient solid-state refrigeration is the harnessing of the synergistic interplay between barocaloric and magnetocaloric effects. In this study, a quantitative phase-field model is developed to elucidate the cooperative enhancement mechanism of multicaloric effects under coupled fields in the ferromagnetic shape-memory alloy Ni₂MnGa. As demonstrated by simulations, the application of hydrostatic pressure results in a linear increase in the martensitic transformation temperature by approximately 24 K/GPa. Concurrently, this pressure-induced process generates a substantial barocaloric response. In the context of the magnetocaloric effect, an anomalous non-monotonic behaviour emerges in proximity to the phase transition. The application of weak magnetic fields results in an inverse magnetocaloric effect, characterised by a positive magnetocaloric coefficient (ΔS > 0), while strong fields reverse this effect, resulting in a negative magnetocaloric coefficient (ΔS < 0). Microstructural analysis corroborates the underlying cause of this effect as being attributed to magneto-structural entropy changes. It is imperative to note that hydrostatic pressure exerts a significant suppression effect on this anomalous magnetocaloric response. Furthermore, the synergistic application of 1GPa pressure and a 0.75 T magnetic field yields an entropy change |ΔS| of 4.46 J·kg^-1·K-1, which exceeds the sum of the individual field effects, thereby demonstrating positive magnetoelastic coupling for synergistic enhancement. The present study offers significant theoretical and simulation-based insights into the design of high-performance multicaloric cooling materials.