Circumventing hysteresis loss via external stress-activated non-spontaneous martensitic phase in a metastable Heusler alloy

Thermal hysteresis associated with first-order martensitic transformations often limits the reversibility of functional responses. Instead of suppressing thermal hysteresis through compositional optimization, we circumvent its adverse effects by exploiting a metastable parent phase in which martensitic transformation is absent under ambient conditions but can be activated by hydrostatic pressure. Above a critical pressure of ~7 kbar, a martensitic phase emerges in the Ni 43 Co 7 Mn 35 In 15 alloy and progressively develops into a complete metamagnetic martensitic transformation at 13 kbar. Although the transformation itself exhibits thermal hysteresis, its activation and suppression are governed exclusively by pressure, resulting in a reversible functional response with negligible pressure hysteresis. This pressure-activated transformation produces a giant baroresistance of 690% at 50 K, originating from the synergistic contributions of electron–spin and electron–lattice scattering in the pressure-induced martensitic phase. Under 13 kbar, a magnetic field of 3 T further induces a magnetoresistance of ~68% near 270 K. A phenomenological thermodynamic model is developed to quantitatively describe the pressure-induced non-spontaneous martensitic transformation. This work demonstrates an alternative strategy for achieving giant hysteresis-loss-free functional responses through pressure-activated non-spontaneous martensitic transformations, providing new opportunities for multifunctional Heusler alloys in sensing, solid-state refrigeration, and spintronic devices.