Executive Summary : | The proposal is all about to develop a potential magnetic refrigerant by modifying the chemical constituent and developing the geometrical compatibility in low-cost and non-toxic Mn-Ni-Si alloy. Since the parent alloy shows a structural transition from orthorhombic to hexagonal in high-temperature regions (above room temperature), achievement of a large magnetocaloric effect at room temperature window is only possible in the two following ways. (i) Iso-structurally alloying with some particular compounds like (Fe2Ge, Mn-Fe-Ge, Fe-Co-Ga, and Ni5Ge). These compounds exhibit hexagonal structure at room temperature region. So, by alloying with these compounds, it will try to stabilize the high-temperature hexagonal phase in the neighborhood of room temperature, and (ii)Substituting foreign elements having less atomic radius as compared to the parent constituent elements. Fe has less atomic radius as compared to Mn. So, substituting Fe will squeeze the unit cell along one particular axis and expand the unit cell along another axis. This results in distortion of the low-temperature phase i.e., the orthorhombic phase, and stabilizes the high-temperature hexagonal phase in the low-temperature region. Controlling the substitution level, the structural transition temperature will be reduced to the room temperature region and it will couple with the low-temperature magnetic transition to produce coupled magneto-structural transition. This will help to achieve a large magnetocaloric effect due to the coupling of both magnetic and structural transitions at a particular temperature. The coupling creates a large magnetization difference across the transition region due to the transformation in the crystal structure. The focus will be on the development of geometrical compatibility between the two crystal symmetries. A transformation matrix will be developed between the two crystal symmetries to observe the closeness between the lattice parameters of both crystal symmetries. The closeness of the calculated middle eigenvalue of the transformation matrix with the unit determines the energy loss associated with the hysteresis loss. With the less difference in eigenvalue will lead the less energy loss. This information will help us to develop a more efficient magnetic refrigerant. The adiabatic temperature change (ΔTad) will be measured by employing direct measurement technique along with other characterizations (Rietveld analysis of temperature dependent XRD patterns, M-H and M-T measurements (estimation of entropy), and DSC measurement). |