dc.contributor.advisor |
Sikder, Prof. Dr. Shibendra Shekher |
|
dc.contributor.author |
Noor, Saroaut |
|
dc.date.accessioned |
2018-08-30T04:41:43Z |
|
dc.date.available |
2018-08-30T04:41:43Z |
|
dc.date.copyright |
2005 |
|
dc.date.issued |
2005-03 |
|
dc.identifier.other |
ID 0055506 |
|
dc.identifier.uri |
http://hdl.handle.net/20.500.12228/440 |
|
dc.description |
This thesis is submitted to the Department of Physics, Khulna University of Engineering & Technology in partial fulfillment of the requirements for the degree of Master of Philosophy, March 2005. |
en_US |
dc.description |
Cataloged from PDF Version of Thesis. |
|
dc.description |
Includes bibliographical references (pages 110-114). |
|
dc.description.abstract |
The typical nanocrystalline alloy known as Finemet with the composition
Fe73.5Cu jNb3Si135B9 has been studied for the soft magnetic properties. The crystalline
phases that evolved after crystallization were studied by X-ray diffraction, crystallization
temperature by DTA and magnetic properties by VSM and impedance analyzer. The change
of magnetic properties with annealing temperature, Ta in the range 400-700°C and annealing
time 1-60 minutes have been investigated. The effect of a two-step annealing on the
permeability Fe735Cu)Nb3Si135B9 alloy has been studied.
The grain size was determined from the line broadening of the fundamental peak using
Scherrers method. Annealed at 555°C, the grain size, the solute silicon content of a-Fe(Si)
grains and the improvement in magnetic softness saturate as a function of time. As
compared to a nanocrystalline alloy obtained by conventional one-step annealing at around
the crystallization temperature, the alloy subjected to preannealing at Ta = 400°C and
subsequent high temperature annealing at Ta=555°C shows similar soft magnetic properties.
An enhancement of initial permeability with increasing annealing temperature was observed
until the annealing temperature TL = 475°C and corresponds to the amorphous relaxed
structure. An abrupt deteroriation of permeability takes place at the beginning of
crystalization beyond which permeability rises dramatically attaining a maximum value at
Ta = 555°C which is attributed to the nanometri grain size effect as a result of averaging out
of effective magnetic anisotropy by exchange interaction and decrease of magnetoelastic
energy. A sharp decrease of permeability above 580°C is assumed to be connected with
iron-boride phase at the beginning of second crystallization stage. The initial permeability
for the optimum annealed sample has been found to be 20786 as compared with 284 for its
amorphous counterpart. The behavior of very high permeability is explained on the basis of
random anisotropy model. From the temperature dependence of magnetization the Curie
temperature of the amorphous state and crystallized ferromagnetic phases like Fe(Si) and
iron-boride phases and the onset of crystallization temperatures of these phases have been
determined. Saturation magnetization measured on the amorphous and annealed samples at
different annealing temperature gradually increases with Ta and show a maximum at the
medium stage of nanocrysallization at Ta 525°C beyond which magnetization decreases.
The results are interpreted on the basis of irreversible structural relaxation as well as
enrichment of the nanograins with Si. |
en_US |
dc.description.statementofresponsibility |
Saroaut Noor |
|
dc.format.extent |
114 pages |
|
dc.language.iso |
en_US |
en_US |
dc.publisher |
Khulna University of Engineering & Technology (KUET), Khulna, Bangladesh. |
en_US |
dc.rights |
Khulna University of Engineering & Technology (KUET) thesis/ dissertation/internship reports are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. |
|
dc.subject |
Complex Permeability |
en_US |
dc.subject |
Nanocrystalline Alloy |
en_US |
dc.subject |
Soft Magnetic Properties |
en_US |
dc.subject |
Nanocrystalline Amorphous Ribbon |
en_US |
dc.title |
Effects of Two Step Annealing on Complex Permeability of Fe-Cu-Nb-Si-B Nanocrystalline Soft Magnetic Materials |
en_US |
dc.type |
Thesis |
en_US |
dc.description.degree |
Master of Philosophy |
|
dc.contributor.department |
Department of Physics |
|