Magnetocaloric effect and multifunctional properties of Ni-Mn-based Heusler alloys

The studies of magnetocaloric properties, phase transitions, and phenomena related to magnetic heterogeneity in the vicinity of the martensitic transition (MT) in Ni-Mn-In and Ni-Mn-Ga off-stoichiometric Heusler alloys are summarized. The crystal structure, magnetocaloric effect (MCE), and magnetotransport properties were studied for the following alloys: Ni 50Mn 50-xIn x, Ni 50-xCo xMn 35In 15, Ni 50Mn 35-xCo xIn 15, Ni 50Mn 35In 14Z (Z=Al, Ge), Ni 50Mn 35In 15-xSi x, Ni 50-xCo xMn 25yGa 25-y, and Ni 50-xCo xMn 32-yFeyGa 18. It was found that the magnetic entropy change, ΔS, associated with the inverse MCE in the vicinity of the temperature of the magneto-structural transition, TM, persists in a range of (125-5) J/(kg K) for a magnetic field change ΔH=5 T. The corresponding temperature varies with composition from 143 to 400 K. The MT in Ni 50Mn 50-xIn x (x=13.5) results in a transition between two paramagnetic states. Associated with the paramagnetic austenite-paramagnetic martensite transition ΔS=24 J/(kg K) was detected for ΔH=5 T at T=350 K. The variation in composition of Ni 2MnGa can drastically change the magnetic state of the martensitic phase below and in the vicinity of TM. The presence of the martensitic phase with magnetic moment much smaller than that in the austenitic phase above TM leads to the large inverse MCE in the Ni 42Co 8Mn 32-yFeyGa 18 system. The adiabatic change of temperature (ΔT ad) in the vicinity of TC and TM of Ni 50Mn 35In 15 and Ni 50Mn 35In 14Z (Z=Al, Ge) was found to be ΔT ad=-2 K and 2 K for ΔH=1.8 T, respectively. It was observed that |ΔT ad|≈1 K for ΔH=1 T for both types of transitions. The results on resistivity, magnetoresistance, Hall resistivity in some In-based alloys are discussed. © 2012 Elsevier B.V