Executive Summary : | The magnetocaloric (MC) materials primarily comprised either GdSi or NiMnGa monolithic systems in view of their potential properties. Their bench-marked properties have been referred in relation to either operating magnetic field or the narrow zone of structural (martensitic / austenite-martensite) freedom. There is always a quest towards magneto-structural tailoring for efficient caloric outputs at low magnetizing / demagnetizing fields. Similar, challenges are faced in ferromagnetic shape memory alloys (FSMAs) wherein the desirable low magnetic field vis-à-vis the microstructure is the key issue to achieve actuation at low energy. In the NiMnGa alloy system, the existence of martensite or austenite phase is highly sensitive to compositional stoichiometry, influencing the magnetocaloric / magnetic shape memory behaviour to a large extent. It is suggested that the thermal limits of this entropy can be widened with the occurrence of intermartensitic transformation i.e the existence of different martensitic phases (monoclinic, tetrahedral etc). Similarly, the shape memory behaviour is also limited by the intensity of magnetizing field as the Heusler systems are strongly anisotropic in character. There is a worldwide research endeavor towards achieving high entropy and refrigerant capacity in magnetocaloric materials while in the case of FSMAs, efforts are targeted towards achieving high recoverable strains with preferable low magnetic fields. The functional properties related to caloric and strain are normally reported at magnetic fields of 5T and above which is supposed to restrict the technological developments towards realization of prototypes. Therefore, it is suggested that if in a Heusler system with intermartensitic transformation, a glassy alloy system in its nanostructured state (amorphous-nanocrystalline) is incorporated, it is supposed to further widen the magneto-structural transformation and the consequent working temperature. Moreover, the isotropic / near isotropic values of amorphous / nanostructured systems are supposed to facilitate caloric effects at lower magnetizing fields. The proposed project would also include direct measurement of magnetocaloric properties through Peltier cells in thermal environments with a magnetic field controlled facility. This would give the caloric efficiency of the materials unlike several reports using indirect methods using thermal variation of magnetizations (Maxwell’s equations). The isotropic nature of glassy / nanostructured phase incorporated in Glassy-Heusler composite would facilitate easy domain wall movement and consequent magnetic shape memory at lower magnetic field. The magnetic shape memory behavior will also be investigated through direct measurement of magnetostrain using 2-terminal capacitance technique. |