Inverse magnetocaloric effects in metamagnetic Ni-Mn-In-based alloys in high magnetic fields

Abstract

Magnetocaloric effects (MCE) in the Ni50Mn35In15, Ni50.2Mn34.85In14.95, and Ni50Mn35In14.25В0.75 Heusler alloys have been studied employing direct measurements of the adiabatic temperature changes (ΔTad) using the extraction method with magnetic field changes (ΔH) up to 14 T, differential scanning calorimetry, and magnetization measurements in magnetic fields up to 14 T. Both the ΔTad and the entropy changes (ΔS) values increase as the martensitic transition approaches the Curie temperature of the austenitic phase. The ΔTad as a function of magnetic field increases up to a maximum value, which depends on the current temperature, and shows a tendency to saturate in high fields. The influence of the rate of magnetic field change and the rate of heating on the ΔTad of Ni50Mn35In14.25В0.75 has been studied. It has been shown that an increase in the heating rate from 7 to 23 K/min results in an increase of ΔTad by about 40% for ΔH = 10 T. The effect is discussed in the terms of the influence the heating rate on the nucleation of the austenitic phase. The results on critical magnetic fields for MCE saturation and kinetic effects are applicable to any other system displaying magnetostructural, first-order phase transition.