  Ni-Mn-based metamagnetic shape-memory alloys exhibit a giant thermal response
to magnetic fields and uniaxial stress which can be utilized in single caloric
or multicaloric cooling concepts for energy-efficient and sustainable
refrigeration. However, during cyclic operation these alloys suffer from
structural and functional fatigue as a result of their high intrinsic
brittleness. Here, we present based on Fe-doping of Ni-Mn-In a microstructure
design strategy which simultaneously improves cyclic stability and maintains
the excellent magnetocaloric and elastocaloric properties. Our results reveal
that precipitation of a strongly Fe-enriched and In-depleted coherent secondary
gamma-phase at grain boundaries can ensure excellent mechanical stability by
hindering intergranular fracture during cyclic loading. In this way, a large
elastocaloric effect of -4.5 K was achieved for more than 16000 cycles without
structural or functional degradation, which corresponds to an increase of the
cyclic stability by more than three orders of magnitude as compared to
single-phase Ni-Mn-In-(Fe). In addition, we demonstrate that the large
magnetocaloric effect of single-phase Ni-Mn-In-(Fe) can be preserved in the
dual-phase material when the secondary gamma-phase is exclusively formed at
grain boundaries as the martensitic transformation within the Heusler matrix is
barely affected. This way, an adiabatic temperature change of -3 K and an
isothermal entropy change of 15 $Jkg^{-1}K^{-1}$ was obtained in 2 T for
dual-phase Ni-Mn-In-Fe. We expect that this concept can be applied to other
single caloric and mutlicaloric materials, therewith paving the way for
solid-state caloric cooling applications.
