Giant reversible inverse magnetocaloric effects in Ni50Mn35In15 Heusler alloys

The magnetic properties and reversibility of the magnetocaloric effect of Ni50Mn35In15 have been studied in the vicinity of the phase transition using magnetization and direct adiabatic temperature change (ΔTad) measurements in magnetic fields up to 14 T. The magnetostructural phase transitions (MSTs) between a martensitic phase (MP) with low magnetization (paramagnetic or antiferromagnetic) and a nearly ferromagnetic austenitic phase were detected from thermomagnetic curves, M(T,H), at the applied magnetic fields up to 5 T. The MST temperature was found to be nearly independent of magnetic field for H < 5 T, and shifted to lower temperature with the further increase of magnetic field to 14 T. A large and nearly reversible inverse magnetocaloric effect (MCE) with ΔTad ∼ −11 К for a magnetic field change of ΔH = 14 T was observed in the vicinity of the MST. The irreversibility of ΔTad was found to be 1 K. A direct ΔTad of +7 K for ΔH = 14 T was detected at the second order ferromagnetic-paramagnetic phase transition. The obtained results have been discussed in terms of the suppression of antiferromagnetic correlations with the application of a strong magnetic field, and a reversibility of the initial magnetic state of the MP with applied magnetic field when the MST coincides with TC.