Date of Award
Master of Science
TITLE: SYNTHESIS AND CHARATERIZATION of CARBON DOPED MANGANESE GALLIUM (MnGaC) ALLOYSMAJOR PROFESSOR: Dr. Saikat TalapatraThis thesis reports on the synthesis and physical property measurement of Carbon (C) Doped Manganese Gallium (MgGa) Alloys. A simple ball milling technique used to dope MgGa with C is discussed. The specific protocols followed to obtain several compositions of these alloys Mn_x Ga_y C_z (x=50,58; y=17,49,50; z=0,1,20) were synthesized. A detail investigation of as produced and high temperature (800oC) annealed Mn_63 Ga_17 C_20 was performed. The outcome of annealing on the crystal structure, magnetic, magnetocaloric and transport properties of Mn_63 Ga_17 C_20is presented. X-ray powder diffraction (XRD) patterns of the pre- and post-annealed samples indicate the cubic lattice structure of the alloys. In general, it was noticed that the as produced sample had a lattice constant of a=5.02 Å , which was reduced to cubic crystal lattice of a=4.40 Å for the annealed samples. The magnetization versus temperature (MvT) measurements performed within a temperature range of 10-350 K showed that the sample undergoes a first-order antiferromagnetic to ferromagnetic transition at (~158 K) and a second-order ferromagnetic to paramagnetic transition at the Curie temperature of (~250 K) in a 5 T field. Such transitions were not observed in the as produced samples. Inverse magnetic entropy changes at martensitic transition temperaturesT_t, and magnetic entropy changes at the Curie temperature T_C were also observed for this sample. The maximum entropy change occurs at the martensitic transition temperature and is ΔS_M=9.43 J/(kg K) with a 5 T field. The relative cooling power (RCPs) was found to be =192.28 J/KG . The results obtained are extremely encouraging from the point of view of materials and compounds needed for magnetic refrigeration and should lead to further investigation of carbon doped/based multifunctional magnetocaloric materials.
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