The martensitic transformation in Ni 2 Mn 1+x Sn 1−x alloys has been investigated within ab-initio density functional theory. The experimental trend of a martensitic transition happening beyond x = 0.36 is captured within these calculations. The microscopic considerations leading to this are traced to increased Ni-Mn hybridization which results from the Ni atom experiencing a resultant force along a lattice parameter and moving towards the Mn atoms above a critical concentration.The presence of the lone pair electrons on Sn forces the movement of Ni atoms away from Sn.While band Jahn Teller effects have been associated with this transition, we show quantitatively that atleast in this class of compounds they have a minor role.

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The magnetocaloric effect (MCE) of (Mn 0.6 Fe 0.4 )NiSi 1−x Al x ( x = 0.07 and 0.08) alloys has been investigated. A phenomenological model has been adopted for simulation of magnetization variation with temperature to investigate magnetocaloric properties such as magnetic entropy change, heat capacity change and relative cooling power. The results indicate the potential of this series of alloys to achieve the MCE at temperatures near Curie temperature ( T C ). These alloys present as prospective candidates for cooling system in a wide temperature interval in the vicinity of room temperature. The maximum change in entropy near T C obtained by phenomenological model has been compared with the Arrott plot method. The results confirm that the phenomenological model is undoubtedly beneficial for the prediction of the magnetocaloric effect of magnetic materials.

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The temperature dependent crystal structure analysis in martensitic phase of Ni 2 Mn 1+x Sn 1−x (x = 0.40 and 0.44) magnetic shape memory alloy is performed using X-ray diffraction. The martensitic phase consists of 4-Layered and 14-Layered orthorhombic structure. The phase fraction of 4-layered and 14-layered orthorhombic structure change with temperature. Interestingly, the magnetic property also changes with temperature and corresponds to structural change temperature.Thus, the exchange coupling constant between original Mn and substituted Mn is calculated, which shows that the 4-layered and 14-layered orthorhombic structures have different strength of antiferromagnetic coupling. The analysis explain the origin of spin glass behavior and unusual exchange bias effect in these systems under zero-field-cooling.

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