Interplay of austenite and martensite phase inside martensite transition regime and its role on magnetocaloric effect and magnetoresistance in Ni-Mn-Sn based Heusler alloy

The first order martensite transition has been observed clearly through magnetic, electronic- and magneto-transport studies in Ni45Mn44Sn11 disordered ferromagnetic shape memory Heusler alloy. The alloy also shows second order ferromagnetic → paramagnetic phase transition, near the Curie temperature of austenite phase. From calorimetric measurement, the lattice entropy due to martensite transformation is found to be 38 Jkg−1K−1, both for heating and cooling cycle. Technologically important noticeably large positive magnetic entropy change has also been clearly noticed in this alloy near martensite phase transition. Maximum isothermal magnetic entropy changes at 275 K for the application of 5 T magnetic field are found to be 15 Jkg−1K−1 and 24 Jkg−1K−1, for field increasing and field decreasing protocol, respectively. A maximum temperature change −5.1 K is observed at 276 K under 5 T magnetic field in adiabatic condition. The noticeable maximum magnetoresistance of −38% for the field change of 5 T is observed at 266 K. The austenite and martensite phase fractions in the sample depend on the magnetic and thermal path history, which are the most possible reasons to observe different values of magnetic entropy change and magnetoresistance in Ni45Mn44Sn11 Heusler alloy at 275 K.