Large magnetocaloric effects can be obtained in Ni-Mn-based Heusler alloys due to the magnetostructural transition between martensite and austenite. This phase transformation proceeds via nucleation and growth. By direct measurements of the adiabatic temperature change $\mathrm{\Delta }{T}_{\mathrm{ad}}$ using different magnetic-field-sweeping rates from 0.01 up to $1500\mathrm{T}{\mathrm{s}}^{-1}$, we study the dynamic behavior of the two Heusler compounds ${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{35}{\mathrm{In}}_{15}$ and ${\mathrm{Ni}}_{45}{\mathrm{Mn}}_{37}{\mathrm{In}}_{13}{\mathrm{Co}}_5$ transforming near room temperature. From these experiments, we conclude that the nucleation process is rather slow in contrast to the relatively fast movement of the phase boundary between martensite and austenite. This is a limiting factor for cooling concepts operating at frequencies beyond 100 Hz. However, the dynamic effects of the transition are negligible in field rates typically used in magnetic refrigeration. These findings are essential considering the suitability of Heusler compounds for energy-efficient solid-state cooling.

• Received 16 December 2015

DOI:https://doi.org/10.1103/PhysRevApplied.5.024013