Quasi-Second-Order Martensitic Phase Transition by Flexomagnetic Coupling

Heusler alloys, known for their first-order martensitic transformation, have found widespread applications in various technological fields. However, the intrinsic hysteresis associated with the phase transitions, combined with the narrow operating temperature range, limits their performance in smart metallic components and energy-efficient devices. Here, we introduce inhomogeneous strain gradients into the wrinkled Ni-Mn-Sn Heusler alloy thin film, facilitating a quasi-second-order martensitic transformation with dramatically reduced hysteresis (ΔT_hysteresis = 3.7 K). This flexomagnetic coupling not only enhances the ferromagnetic interaction but also broadens the operating temperature window (T_o = 260 K) for magnetic entropy change, offering substantial improvements in saturation magnetization (M_s = 71.3 emu/g) and effective refrigeration capacity (RC_eff = 340.6 J·kg^-1 under 50 kOe). Our findings offer a promising strategy for designing advanced phase-transition materials with applications in magnetic refrigeration and microscale smart systems.