Influence of the martensitic transformation kinetics on the magnetocaloric effect in Ni-Mn-In

Ni-Mn-based Heusler compounds exhibit giant magnetocaloric effects upon the magnetostructural transformation between low-temperature, low-magnetization martensite and high-temperature, high-magnetization austenite. Together with our colleagues from Helmholtz-Zentrum Dresden-Rossendorf we analyzed dynamical effects of the reverse martensitic transformation by simultaneous adiabatic temperature change ΔTad and strain Δl/l0 measurements in varying magnetic field-sweep rates. Our experiments demonstrate a pronounced delay at the end of the reverse martensitic transformation when a critical field rate of 865 Ts-1 is exceeded which is related to the martensite annihilation process. In consequence, the field hysteresis increases and higher fields are required to saturate the transition. These findings illustrate that kinetic effects in Heusler compounds and potentially other first-order materials can strongly affect the magnetic cooling cycle, especially when utilising a multicaloric “exploiting-hysteresis cycle” where high magnetic field-sweep rates are employed.