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

Abstract: The inverse magnetocaloric effect (MCE) in Ni-Mn-based Heusler compounds occurs during the magnetostructural transition between low-temperature, low-magnetization martensite and high-temperature, high-magnetization austenite. In this study, we analyze the metamagnetic transformation of a $Ni_{49.8}Mn_{35}In_{15.2}$ compound by simultaneous adiabatic temperature change and strain measurements in pulsed magnetic fields up to 10 T. We observe an adiabatic temperature change of -10 K and a strain of -0.22 % when the reverse martensitic transition is fully induced at a starting temperature of 285 K. By a variation of the magnetic field-sweep rates between 316 Ts$^{-1}$, 865 Ts$^{-1}$ and 1850 Ts$^{-1}$, the transitional dynamics of the reverse martensitic transformation have been investigated. Our experiments reveal an apparent delay upon the end of the reverse martensitic transformation at field rates exceeding 865 Ts$^{-1}$ which is related to the annihilation of retained martensite. As a consequence, the field hysteresis increases and higher fields are required to saturate the transition. In contrast, no time-dependent effects on the onset of the reverse martensitic transformation were observed in the studied field-sweep range. Our results demonstrate that kinetic effects in Heusler compounds strongly affect the magnetic cooling cycle, especially when utilising a multicaloric "exploiting-hysteresis cycle" where high magnetic field-sweep rates are employed.