| Description |
In recent years, ferromagnetic shape memory alloys have gain considerable attention due to versatile interesting properties exhibited by them such as martensitic transformation, larger magnetocaloric effect, magnetic field induced strain, exchange bias, etc. One of the extensively studied ferromagnetic shape memory alloy Mn2NiGa with high Curie temperature (~588K)exhibits 4% shape memory effect.The influence of the chemical substitution of Cu at Ni site, in Mn2NiGa, on the structural, magnetic, magnetocaloric and magnetoresistance properties has been investigated.The presence of the stress induced modulated monoclinic structure along with the cubic phase has been observed in room temperature X-ray diffraction (XRD) measurements. The temperature dependent magnetization measurement suggests the existence of martensitic phase transition in Mn2Ni1-xCuxGa alloy. With the increase in Cu content the martensitic transition temperature decreases, whereas 10% Cu substitution at Ni – site results in complete suppression of martensitic phase where the magnetization shows ferromagnetic behavior in the temperature range of 5 – 390K. Magnetoresistance (MR) measurement as a function of applied magnetic field shows highly asymmetric behavior in MR about the direction of magnetic field in the samples studied.Apart from chemical substitution, residual stress introduced during the processing of the alloys playscrucial role in stabilizing the structure. By varying the cooling rate, kinetics of the structural relaxation can be altered.In order to understand the role of residual stress in stabilizing the martensite structure results of the studies on the effect of annealing on the martensitic transformation in Mn2NiGa alloys prepared with different cooling path (rate) will also be presented.
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