MAGNETIC PROPERTIES OF Co AND Mn SUBSTITUTED Fe–Zr–B ALLOYS PREPARED BY MELT SPINNING AND MECHANICAL ALLOYING PROCESSES
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Date
2009
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Abstract
Fe-Zr-B based amorphous and nanocrystalline alloys are well known soft magnetic materials which are characterized by high saturation magnetization (MS) and low coercivity (HC). These soft magnetic alloys find wide applications in highper formance magnetic parts such as in electronic devices, common mode choke-coils, power electronics, bead cores, electrical noise absorbers, magnetic switch cores, transformers, current sensors and electromagnetic shielding, magnetic refrigerants, magnetoimpedance devices etc. These materials are prepared through melt spinning and mechanical alloying (MA) routes by controlled crystallization of amorphous precursors and structural reduction of crystallites by the introduction of defects and dislocations, respectively. Conventional methods of improving the intrinsic and extrinsic soft magnetic properties focus on tailoring composition, control of microstructure with heat treatment under different environments, reduction of HC, increase of MS and control of intergranular exchange coupling in the amorphous and nanocrystalline materials. Hence, preparing Fe-Zr-B based amorphous and nanocrystalline alloys through different synthesis routes and understanding the correlation between the structural and magnetic properties of these materials over a wide composition range are very much important from basic physics as well as application view point. This thesis work aims to (i) understand the effect of substituting elements (B, Co, and Mn) on the stability of amorphous phase and temperature dependent magnetic properties of amorphous (a-)Fe-Zr based alloys prepared by melt spinning and MA routes, (ii) study the magnetocaloric effect (MCE) in amorphous ribbons, and (iii) investigate the effect of magnetic field annealing on the improvement of soft magnetic properties of the melt-spun ribbons in correlation with microstructure and magnetic domain structure. The thesis is presented in eight chapters. The first chapter serves as a general introduction to the materials of interest to this work, motivation behind the work with historical perspective from the literature and the objectives of the thesis work.
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Supervisor: A. Perumal
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PHYSICS