The giant inverse magnetocaloric effect (MCE) observed in Heusler alloys holds significant promise for magnetic refrigeration. However, its practical application is hampered by hysteresis, irreversibility, and, critically, the degradation of MCE under cyclically applied magnetic fields. In this study, we propose a paradigm shift: instead of suppressing the irreversibility of the martensite-austenite magnetostructural phase transition (MSPT), we propose to control and utilize it. We present a comprehensive investigation of the irreversible phase transition dynamics in the ${\mathrm{Ni}}_{47}{\mathrm{Mn}}_{40}{\mathrm{Sn}}_{12}{\mathrm{Cu}}_1$ alloy, employing direct measurements of the adiabatic temperature change $\left(\mathrm{\Delta }{T}_{\mathrm{ad}}\right)$ in cyclic fields up to 8 T, in situ XRD analysis, and first-principles DFT and Monte Carlo calculations. Our findings reveal that the irreversibility of the phase transition contributes an additional component to the giant inverse MCE, enhancing the overall effect by up to 35%. We identify a critical dependence of the magnitude and sign of $\mathrm{\Delta }{T}_{\mathrm{ad}}$ on the magnetic field sweep rate and thermal history, which is governed by nucleation and growth kinetics. Rapid cooling is shown to induce to kinetic arrest, resulting in a mixed two-phase state with comparable martensite and austenite fractions, where the direct and inverse MCE contributions compensate each other, leading to the “collapse” of the giant inverse MCE. Our results demonstrate a new route to enhance and stabilize the giant inverse MCE through the controlled utilization of irreversibility and the optimization of the operating cycle kinetics. This approach paves the way for the rational design of magnetic materials and operational protocols for high-performance magnetic refrigerators.

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• Magnetic phase transitions
• Phase separation
• Phase transitions
• Thermomagnetic effects
• Density functional theory
• First-principles calculations
• Materials modeling
• Monte Carlo methods
• X-ray diffraction