| dc.description |
Alhamdulillah, I express my humble gratitude to Allah Rabbul A’lameen whose unceasing
and everlasting blessings enabled me to complete the research and submit the thesis in time.
I express my profound gratitude to my respected supervisor Major Md Mahabubar
Rahman Shah, MPhil, PhD, Department of Science and Humanities (Physics Division),
Military Institute of Science and Technology (MIST) for his constant advice, constructive
criticism and inspiration during the whole period of present investigation. Moreover, I am
owed to him for his additional caring and solving different administrative issues related to
this experimental work.
With deep respect and honor, I would like to express fervently my earnest gratitude and
indebtedness to my respected thesis Co-supervisor Prof Dr Mohammad Belal Hossen,
Physics Department of Chittagong University of Engineering and Technology (CUET) for
rendering me opportunity to perform my research work with all-out support and invaluable
guidance throughout this academic journey. He has educated me the execution of research
methodology and taught how to present the work in a clear and simple way. I would also like
to thank him for his friendship, empathy and mental support in different critical situations.
I am deeply grateful to Colonel Md Shahinoor Alam, SPP, PEng, Head, Department of
Science and Humanities, Military Institute of Science and Technology (MIST), for his
cooperation and coordination at different stages of the work. His valuable suggestions, timely
guidance and constructive criticisms are praise-worthy and valuable assets for my life. I am
also extremely grateful to the MIST authorities for providing the necessary financial grant for
the research.
I would like to thank all the respected teachers of the Department of Science and Humanities,
MIST and Department of Physics, CUET, special thanks to Captain M Ziaul Ahsan, PhD
(Ex Head of the Department), Lieutenant Colonel Brajalal Sinha, PhD, Major Tahmina
Rahman of MIST for their cooperation. My special thank goes to affectionate junior brother
M. Faishal Mahmood, a PhD student at Department of Physics in CUET who was a copartner in Functional Nanomaterials Laboratory. I am also thankful to my respected mentor
Colonel Eare Md Morshed Alam, MPhil, PhD for his consistent mental support. I also
would like to convey my thanks to the employees of the department of Physics, CUET and
MIST for their co-operation and help specially to Mr Sohel Rana.
I would like to acknowledge the moral support and the sustained inspiration of my loving
wife Farhana Rahman and affectionate son Fasih Ur Rahman along with all other
members of my family. This dissertation would have never been possible without their love,
affection, encouragement and sacrifices.
Finally, I am extremely grateful to my blessed parents, siblings and uncles for their love,
caring, sacrifices, and prayers for preparing and educating me for my future. |
en_US |
| dc.description.abstract |
Maintaining nanoscale properties in a high-density bulk form of ferrite prepared from
powdered nanoparticles is quite desirable in many high frequency applications. Various
Ni0.5-xMnxCu0.2Cd0.3Fe2O4 (NMCCFO, x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) dense bulk ferrites
were consolidated from nano-crystalline powders by the sol-gel auto-combustion technique.
Commercially available different nitrate salts of the ingredients were mixed thoroughly in
stoichiometric amount and were calcined at 700°C for 5 h. Pellet and toroid shaped samples
prepared from each composition were sintered at 1200°C for 5 h.
X-ray diffraction (XRD) was used to carry out the structural analyses. The XRD data confirm
that all compositions are single phase spinel structure. The lattice constant increase with
increasing Mn content which is a clear indication of Mn incorporation in spinel structure. The
theoretical density and the bulk density decrease but the porosity increases with increasing
Mn content. The Rietveld refinement method confirms the goodness of fit with refined XRD
data of NMCCFO for different Mn content. Rietveld technique is also adopted to determine
the cation distribution between tetrahedral and octahedral sites and shows that maximum
migration of Fe ions from A to B-sites occurs for x = 0.2 of Mn content.
The Maximum Entropy Map analysis reveals the variation of the electron density with
increasing Mn content and the presence of strong covalent bonding. Field emission scanning
electron microscopy (FE-SEM) is used to carry out the surface morphology analyses. The
average grain sizes increases from 1 μm to 4 μm for all compositions except x = 0.5 of Mn
content. Energy dispersive X-ray (EDX) findings confirm the absence of traceable impurities
and presence of Ni, Mn, Cu, Cd, Fe, and O in the samples.
The dielectric measurements as a function of frequency and compositions are carried out at
room temperature in the frequency range 100 Hz to 100 MHz. The dielectric constant (ε
/
) and
the dielectric loss tangent (tan δ) remains high at low frequency but becomes independent of
frequency at higher frequencies for all the compositions of NMCCFO. This phenomenon may
be explained by the Maxwell–Wagner model. The ac conductivity (σac) is derived from the
dielectric measurements and it increases with increasing of frequency for all the compositions
of NMCCFO.
Frequency dependence of real (M/
) and imaginary (M//) parts of the electric modulus and real
(Z
/
) and imaginary (Z
//) parts of the complex impedance for different composition are
measured at room temperature. The Cole-Cole plots (M/ vs M//) of electric modulus exhibit a
tendency of formation of a single semicircular arc for all compositions indicates the existence
of single-phase nature of the materials as well as the improvement in conductivity. Also, the
Cole-Cole plots (Z/ vs Z//) of complex impedance exhibit a tendency of formation of
semicircles end in the high frequency region. It explains the dominancy of the grain
boundary.
The vibrating sample magnetometer (VSM) was used for magnetization measurement at
room temperature. From the hysteresis loop, the saturation magnetisation (Ms), remanent
magnetisation (Mr), coercivity (Hc), the ratio (R) of Mr and Ms, anisotropy constant (K1), and
magnetisation magnetic moment (μB) are calculated. All the compositions show the nature of
soft ferrite due to the small amount of remanence and coercivity. Theoretical law of approach
to saturation (LAS) shows that the values for both the saturation magnetization (Ms) and
anisotropy constant (K1) are lesser than the experimental value.
Therefore, the unique combination of electric and magnetic properties like low dielectric loss
tangent, high ac conductivity and soft ferrite like behavior make the NMCCFO materials
suitable for manufacturing high frequency devices like Multilayer Ferrite Chips Inductor
(MLFCI), phase shifters, switches, etc. |
en_US |
