In-situ phase transformation studies of Ni48Mn39In13 melt-spun ribbons

The phase transformation in Ni48Mn39In13 melt-spun ribbons has been studied by employing in-situ transmission electron microscopy (TEM) techniques. At room temperature, the investigations showed the martensite phase consisting of plates with internal stacking faults. This phase exhibited the presence of 7M and 5M modulations. In addition, a small volume fraction of the austenite phase was observed. Upon in-situ heating from room temperature to 95 degrees C, the martensite phase transformed to austenite phase. However, in the subsequent cooling-heating cycles, the martensite phase was retained at high temperature. We discuss our experimental observations and the possible mechanisms for the stabilization of the martensite phase due to thermal cycling. (c) 2012 Elsevier Ltd. All rights reserved

Structure, magneto-structural transitions and magnetocaloric properties in Ni50-xMn37+xIn13 melt spun ribbons

Melt spun Ni50-xMn37+xIn13 (2 <= x <= 5) ribbons were investigated for the structure, microstructure, magneto-structural transitions and inverse magnetocaloric effect (IMCE) associated with the first-order martensitic phase transition. The influence of excess Mn in Ni site (or Ni/Mn content) on the martensite transition and the associated magnetic and magnetocaloric properties are discussed. It was found that with the increase in Mn content, the martensitic transition shifted from 325 to 240 K as x is varied from 2 to 4, and the austenite phase was stabilized at room temperature. The x=5 ribbon did not show the martensitic transition. For the x=3 ribbon, the structural and magnetic transitions are close together unlike in the x=4 ribbon in which they are far (similar to 60 K) apart. The zero field cooled and field cooled curves support the presence of exchange bias blocking temperature due to antiferromagnetic interactions in the ribbons. A large change in the magnetization between the martensite and austenite phases was observed for a small variation in the Ni/Mn content, which resulted in large IMCE. A large positive magnetic entropy change (Delta S-M) of 32 J/kg K at room temperature (similar to 300 K) for a field change of 5 T with a net refrigeration capacity of 64 J/kg was obtained in the Ni47Mn40In13 ribbon. (C) 2011 Elsevier B.V. All rights reserved