Magnetocaloric effect and critical behavior study in NiMnSnIn Heusler alloys

In the present work, polycrystalline Ni50Mn36Sn14-xInx (x = 0, 1, 2 and 3) Heusler alloys were prepared. The influence of In substitution for Sn on the crystal structure, martensitic transition (MT) and magnetic properties have been investigated for these alloys. Structural analysis indicate that the samples possess L21 structure at room temperature. With increasing In content, the martensitic transition shifts to a higher temperature, while the Curie temperature of austenite phase moves to a lower temperature. The maximum entropy change (ΔSM)max near the martensitic transition is found to be 8.4 J/kgK, 9.8 J/kgK, 10.1 J/kgK and 19.2 J/kgK for x = 0, 1, 2 and 3 respectively, for a field change of 50 kOe. The entropy change around the Curie temperature of the austenite phase is found to be - 2.9 J/kgK, −1.8 J/kgK, −4.1 J/kgK and −3.9 J/kgK respectively for x = 0, 1, 2 and 3 alloys, for a field change of 50 kOe. The effective RCP values are 80 J/kg, 15.6 J/kg, 65.8 J/kg and 69.4 J/kg for x = 0, 1, 2 and 3 alloys respectively, near the first order transition region. The RCP values are higher around the second order transition region due to the broad nature of ΔSM curves. The corresponding values are 114 J/kg, 92 J/kg, 121 J/kg and 132 J/kg for x = 0, 1, 2 and 3 alloys, respectively. Moreover, the critical behavior of Ni50Mn36Sn14-xInx (x = 1, 2 and 3) Heusler alloys around the ferromagnetic-paramagnetic transition region of austenite phase is studied from the field dependence of magnetic entropy change. The critical exponent values are close to the theoretical prediction of mean field model with a slight deviation.