Giant field-induced adiabatic temperature changes in In-based off-stoichiometric Heusler alloys

Direct measurements of the adiabatic temperature change (DTAD) of Ni50Mn35In14.5B0.5 have been done using an adiabatic magnetocalorimeter in a temperature range of 250-350 K, and with magnetic field changes up to Delta H = 1.8 T. The initial susceptibility in the low magnetic field region drastically increases with temperature starting at about 300 K. Magnetocaloric effects parameters, adiabatic temperature changes, and magnetic entropy changes were found to be a linear function of H-2/3 in the vicinity of the second order transitions (SOT), whereas the first order transitions do not obey the H-2/3 law due to the discontinuity of the transition. The relative cooling power based on the adiabatic temperature change for a magnetic field change of 1.8 T has been estimated. Maximum values of Delta T-AD = -2.6K and 1.7 K were observed at the magnetostructural transition (MST) and SOT for Delta H = 1.8 T, respectively. The observed DTAD at the MST exceeds the DTAD for Ni50Mn35In14X with X = In, Al, and Ge by more than 20% and is larger than the Gd based Heusler alloys.