Magnetic Shape Memory Heuslers for Caloric Applications—The Crucial Role of Microstructure in the Martensitic Transformation

The vast family of Ni-Mn based Heusler alloys provides an extended playground of physical properties. The interplay between a martensitic transformation and magnetically ordered states gives rise to a series of functional properties that can be exploited in different technological sectors, among which remote actuation, solid state refrigeration and thermomagnetic generation. Their excellent responsiveness to external fields, i.e. magnetic field, pressure and stress and their combined application, makes them promising for multifunctional exploitation. On the other hand the hysteretic character of the martensitic transformation cripple the performance of these materials in cyclic operations.<br/><br/>In my talk I will present some recent results on NiMn-based Heuslers, including nano/microscale materials obtained by different fabrication methods, i.e. epitaxial thin films [1], patterned micro/nanostructures [2], mechanically-milled particles [3]. Thin films and micro/nanostructures are of particular interest not only for the realization of miniaturized new-concept devices, but also for providing insights into the magneto-structural coupling at the different length scales, suggesting possible strategies for the optimization of material performances.<br/>The talk will focus on microstructure tuning and microstructure-related effects on the martensitic transformation, in view of the possible exploitation of this class of materials in smart and caloric applications.<br/><br/>[1] M. Takhsha Ghahfarokhi et al., Acta Mater. <b>23</b> (2021), 117356.<br/>[2] M. Takhsha Ghahfarokhi et al., Appl. Mater. Today <b>23</b> (2021), 101058.<br/>[3] G. Cavazzini et al., J. Alloys and Comp. <b>872</b> (2021) 159747; J. Alloys and Comp. <b>906</b> (2022) 164377.