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: Ni50Mn50-xInx, Ni50-xCoxMn35, Ni50Mn35-xCoxIn15, Ni(50)Mn(35)In(14)Z (Z=Al, Ge), Ni50Mn35In15-xSix, Ni50-xCoxMn25+yGa25-y and Ni(50-x)Co(x)Mn(32-y)FeyGa(18). It was found that the magnetic entropy change, Delta S, 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 Delta H=5 T. The corresponding temperature varies with composition from 143 to 400 K. The MT in Ni50Mn50-xInx (x=13.5) results in a transition between two paramagnetic states. Associated with the paramagnetic austenite-paramagnetic martensite transition Delta S=24 J/(kg K) was detected for Delta H=5 T at T=350 K. The variation in composition of Ni2MnGa 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(42)Co(8)Mn(32-y)FeyGa(18) system. The adiabatic change of temperature (Delta T-ad) in the vicinity of TC and TM of Ni50Mn35In15 and Ni(50)Mn(35)In(14)Z (Z=Al, Ge) was found to be Delta T-ad= -2 K and 2K for Delta H=1.8 T, respectively. It was observed that vertical bar Delta T-ad vertical bar approximate to 1 K for Delta H=1 T for both types of transitions. The results on resistivity, magnetoresistance, Hall resistivity in some In-based alloys are discussed. (C) 2012 Elsevier BY. All rights reserved.