Magnetostructural transformation, microstructure, and magnetocaloric effect in Ni-Mn-Ga Heusler alloys

Abstract

Magnetostructural transformation and the associated magnetic entropy change were investigated in Ni-rich ferromagnetic Heusler alloys. A direct transformation from the ferromagnetic martensite phase to the paramagnetic austenite phase was observed in selected Ni54.8Mn20.3Ga24.9 and Ni55Mn18.9Ga26.1 two-alloy compositions. The magnetic and martensitic transformations were incurred at nearly the same temperature (351 K) in the Ni54.8Mn20.3Ga24.9 alloy. Such a typical composition involves a change of the magnetic entropy ΔSM as large as −7.0 J/kg K at 332 K in an applied magnetic field of 1.2 T.