Magnetocaloric effect and magnetic phase diagram of Ni-Mn-Ga Heusler alloy in steady and pulsed magnetic fields

The work is devoted to the study of the phenomenon of irreversibility of the magnetocaloric effect (MCE) in the vicinity of the magnetostructural phase transition (PT) in Ni-Mn-Ga Heusler alloys. For this purpose, the MCE was studied by the direct method in stationary (up to 14 T) and pulsed magnetic fields (up to 50 T), and a magnetic phase diagram was constructed. Using a specially designed microscope, in-situ studies of the magnetostructural phase transition were carried out in magnetic fields of up to 14 T. Comparing the results of the MCE with those of the phase diagram, as well as in-situ studies, made it possible to determine the width of the irreversible MCE region. In-situ studies have shown, that the main reason of the occurrence of the irreversible MCE is the presence of the residual martensite formed as a result of the first magnetization of the sample. The results are discussed within the framework of Landau's phenomenological PT theory, which predicts the disappearance of thermal hysteresis under a field of 30 T. Within the framework of the same theory, a recommendation is made to reduce the value of the critical field and, as a result, the width of the hysteresis.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This work focuses on the investigation of the irreversibility of the magnetocaloric effect (MCE) near the magnetostructural phase transition (PT) in Ni-Mn-Ga Heusler alloys. By using direct method and in-situ studies, the width of the irreversible MCE region was determined, and it was found that the presence of residual martensite is the main cause of the irreversible MCE.