Inverse-direct magnetocaloric effect crossover in Ni47Mn40Sn12.5Cu0.5 Heusler alloy in cyclic magnetic fields

Abstract

The results of direct studies of the magnetocaloric effect (MCE) of the Ni47Mn40Sn12.5Cu0.5 Heusler alloy in cyclic magnetic fields are presented. It is shown that in cyclic magnetic fields, the MCE value near the magnetostructural phase transition depends on the rate of temperature scanning. A higher rate of change in the sample temperature causes the MCE to have a greater value. The observed effect is explained by irreversible phase transition, induced by a magnetic field, from a low-symmetry martensitic phase to a high-symmetry austenitic phase. Moreover, it is observed only within the temperature hysteresis loop of the magnetostructural phase transition. Such materials, despite the considerable MCE values under a single application of the magnetic field, are unpromising due to a strong change in the magnetocaloric properties in cyclic magnetic fields.