Transformation process dependent magnetocaloric properties of annealed Ni50Mn18Cu7Ga25 ribbons

摘要

The properties related to magnetocaloric effect (MCE) of annealed Ni50Mn18Cu7Ga25 ribbons were studied in connection with their microstructural features and magnetostructural transformations. The differences in magnetic entropy change between the reverse and direct austenite-to-martensite transformation processes lie in the magnetic field induced martensitic transformation. It occurs uniquely during the direct transformation but not reciprocal in the reverse transformation, which results in the relatively lower value of maximum Delta S-M but higher delta T-FWHM of the Delta S-M curve for the direct transformation (Delta S-M = 17.8 Jkg(-1)K(-1), delta T-FWHM = 6 K) with respect to those of the reverse transformation (Delta S-M = -32.1 Jkg(-1)K(-1), delta T-FWHM = 3 K) under magnetic field change mu(o)Delta H of 5 T. These transformation singularities have a deep connection with the microstructural configurations of the parent and product phases. The present study provides fundamental information necessary to understand the transformation dependent MCE of ferromagnetic functional alloys. (C) 2016 Elsevier B.V. All rights reserved.