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Title: Structural and martensitic phase transformations in nanostructured Ni2MnGa ferromagnetic shape memory alloys
Researcher: Vallalperuman K
Guide(s): Mahendran M
Keywords: Nanostructure, ferromagnetic shape memory alloys (FSMAs), nanomechanical, Ni-Mn-Ga, X-ray diffraction
Upload Date: 20-Jan-2014
University: Anna University
Completed Date: 
Abstract: Ferromagnetic shape-memory alloys (FSMAs), in particular Ni-Mn-Ga alloys are keenly studied materials due to their large strain up to 10% and rapid response to magnetic field. This makes it possible to realize novel actuators and sensors. So far, the research on Ni-Mn-Ga has focused on its bulk, melt spin ribbon and thin film properties but for the fabrication of nanocomposites, the material should be in powder form to develop the nanomechanical components. The thesis describes the preliminary investigation of Ni-Mn-Ga single crystals to have fundamental knowledge on crystal structure and MT. The transformation temperature of Ni-Mn-Ga single crystals is extremely sensitive to composition. It is found that martensitic temperatures abruptly increase with increasing Mn concentration whereas Curie transition (TC) to decrease. An important part of this thesis is to examine the crystal structure, MT and magnetic properties of nanostructured Ni-Mn-Ga alloys. Various compositions of the off-stoichiometric Ni-Mn-Ga nanoparticles were prepared by ball milling and post annealing method. A systematic exploration of the composition-structure relationship has been performed using X-ray diffraction. Several martensitic structures including non modulated tetragonal, orthorhombic (7M) and coexistence of martensite and austenite phases have been identified. In addition, ball milling also severely weakens the magnetization of the alloy which is apparently caused by the destruction of Mn Mn ferromagnetic exchange induced. Thermo hysteresis curve of the disordered powder was linear and revealed very low moment indicative of paramagnetic nature. Annealing at elevated temperatures is effective in restoring the ferromagnetism. Both disordered and nanocrystalline structure coexisted in the ball-milled sample; such a nanomagnetic structure is considered to be ideal for soft magnetic material. newline newline newline
Pagination: xix, 128
Appears in Departments:Faculty of Science and Humanities

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02_certificates.pdf154.67 kBAdobe PDFView/Open
03_abstract.pdf26.2 kBAdobe PDFView/Open
04_acknowledgement.pdf18.32 kBAdobe PDFView/Open
05_contents.pdf76.61 kBAdobe PDFView/Open
06_chapter 1.pdf2.14 MBAdobe PDFView/Open
07_chapter 2.pdf417.39 kBAdobe PDFView/Open
08_chapter 3.pdf450.54 kBAdobe PDFView/Open
09_chapter 4.pdf3.83 MBAdobe PDFView/Open
10_chapter 5.pdf28.12 kBAdobe PDFView/Open
11_references.pdf127.34 kBAdobe PDFView/Open
12_publications.pdf23.51 kBAdobe PDFView/Open
13_vitae.pdf15.61 kBAdobe PDFView/Open

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