Strain-driven magnetostructural relaxation 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-dependent response remains underexplored, despite being essential for understanding and further optimizing the magnetostructural transformation. 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 −1 . By implementing a time-dependent measurement protocol, we access both the field-driven and time-dependent 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. 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.