Magnetic entropy and magnetocaloric effect of ferromagnetic Heusler alloys Ni2Mn0.75Cu0.25Ga and Ni2MnGa0.88Cu0.12

The magneto-structural transformation and the associated magnetic entropy change were studied in the ferromagnetic shape memory alloys Ni2Mn0.75Cu0.25Ga and Ni2MnGa0.88Cu0.12 by using magnetization measurements performed around the martensite transformation temperature TM and the Curie temperature TC. The direct transition from the paramagnetic austenite phase (PM phase) to the ferromagnetic martensite phase (FM phase) was observed in both alloys. In a magnetic field of 2.0 T, the Ni2Mn0.75Cu0.25Ga and Ni2MnGa0.88Cu0.12 alloys showed large magnetic entropy changes of −ΔSM = 15.2 J/kg K at 302 K and −7.5 J/kg K at 333 K, respectively. The magnetic entropy change of Ni2Mn0.75Cu0.25Ga is larger than that of the polycrystalline Ni2.19Mn0.81Ga alloy. Theoretical calculations were also performed, and they agreed well with the experimental determinations of −ΔSM.

► Magneto-structural transformation and associated magnetic entropy change were studied.
► The direct magneto-structural transitions were observed.
► In the magnetic field of 2.0 T, two alloys involve large magnetic entropy changes.
► Theoretical calculations agreed well with the experimental determinations.