Strain-driven magnetostructural kinetics revealed in Heusler alloys

First-order magnetostructural transitions underpin the functionality of many magnetocaloric materials and form the basis of emerging solid-state cooling technologies. However, their time-driven response remains underexplored, despite containing intrinsic kinetic information essential for understanding and further optimizing the transformation dynamics. Here, we developed a unique experimental setup to perform simultaneous measurements of magnetization, strain, and temperature change in the benchmark Heusler-alloy Ni–Mn–In under magnetic fields up to 30 T at sweep rates of 10 T/min. By implementing a kinetic measurement protocol, we access both the field-driven and time-driven evolutions of magnetic and structural order parameters along the forward and reverse transition directions. While magnetization rapidly stabilizes after field halting, the probed strain response continues to evolve over extended timescales, indicating distinct relaxation behavior of the measured properties. Quantitative analysis using an extended Avrami–Hay model reveals a secondary diffusive contribution that is required to describe this slow strain evolution. This long-term kinetic dominance of strain also coincides with the substantial structural entropy change characteristic of the Ni–Mn–X family, relating the primary entropy contributor to the strain’s extended response. These results provide a general framework for probing coupled order parameters in first-order multifunctional materials, offering insights for the development of efficient caloric devices.