http://103.99.128.19:8080/xmlui/handle/123456789/109 Thesis published in Dept. of Physics 2026-11-14T12:14:25Z http://103.99.128.19:8080/xmlui/handle/123456789/613 Study of structural, dielectric, electrical and magnetic properties of NiCdal bulk ferrites. Mohammed, Nur \(\text{Ni}_{0.65}\text{Cd}_{0.35}\text{Fe}_{2-x}\text{Al}_x\text{O}_4\) (0 ≤ x ≤ 0.060 with step 0.015) disc and toroid shaped bulk specimen has been fabricated from the sol-gel synthesized nanocrystalline powders and illustrated how influence of Al substitution in its structural, optical, dielectric, electric and magnetic properties. Structural characterization has been analyzed using X-ray diffraction (XRD) and Fourier Transform Infrared Spectra (FTIR) data. Theoretical analysis has been carried out using the Rietveld refinement method from the experimentally obtained XRD data. Crystallite size has been computed (39-36) nm, (43-36) nm, (64-46) nm, (44-38) nm applying Scherer's formula, modified Scherer's formula, Williamson-Hall method and Size-strain plot method respectively. Surface morphology as well as microstructure have been analyzed using Scanning Electron Microscope (SEM). From FTIR spectra, like force constant, stiffness constant, elastic moduli, wave velocities and Debye temperature have been estimated. Intrinsic magnetic hysteresis parameters at room temperature and temperature dependent magnetization have been measured using the Physical Properties Measurement System (PPMS). Law of Approach to saturation applied for theoretical analysis as well as magnetic entropy changes for relative cooling power estimated which is an important for magnetic caloric refrigeration application. Using optical properties measurement, Kramers Kroning (K-K) relation is employed to compute the refractive index (n) and the extinction coefficient (K). Initial permeability spectra have been obtained from 20 to 10MHz by an impedance analyzer in order to understand the high frequency application. Dielectric, permittivity, dielectric loss tangent and AC conductivity have been measured using impedance analyzer data. Complex impedance and modulus spectra have been calculated from impedance data as well as theoretical analysis of the grain and grain boundary parameters Rg, Rgb, Cg, Cgb using Z-sim software. A Master of Philosophy (M.Phil) Thesis in Physics Department at Chittagong University of Engineering and Technology (CUET). 2025-10-14T00:00:00Z http://103.99.128.19:8080/xmlui/handle/123456789/588 EFFECT OF CHROMIUM SUBSTITUTION ON THE STRUCTURAL, ELECTRICAL, AND MAGNETIC PROPERTIES OF Ni-Mn-Zn FERRITES Bibi, Siyara; ID:, 15MPHY005P Cr3+ substituted Ni-Mn-Zn, a chemical composition of ferrites that includes Ni0.6Mn0.2Zn0.2CrxFe2-xO4 ferrites (where x = 0.00, 0.05, 0.10, 0.15, 0.20), were synthesized via the solid-state reaction method. Inside a muffle furnace, these samples are heated to 1100°C for four hours and then left to cool down naturally. The ferrites were then further studied using X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Impedance analyzer, and Vibrating Sample Magnetometer (VSM). The XRD data confirmed the formation of a cubic spinel structure without secondary phases. A reduction of the lattice constant due to Cr3+ presence is observed because of having smaller Cr ions (0.62Å) than Fe ions (0.645Å). The SEM images confirmed the homogenous distribution of grains, where the grain sizes of the Cr3+-substituted composition are found to be less than that of the Ni-Mn-Zn basic composition, except for x=0.10. The Cr3+-substituted compositions exhibit a larger dielectric constant than the x=0.0 composition. The AC resistivity value is also less for the Cr3+-substituted compositions. The VSM was utilized to investigate the magnetic properties. The saturation magnetization, remanent magnetization, and coercive field were significantly influenced by the Cr3+ substitution because Cr3+ has a lower magnetic moment than Fe3+.. A decrease in magnetic permeability has also been observed owing to the Cr3+ substitution. A Master of Philosophy (M.Phil.) Thesis in Physics Department at Chittagong University of Engineering and Technology (CUET). 2025-06-23T00:00:00Z http://103.99.128.19:8080/xmlui/handle/123456789/576 STUDY OF STRUCTURAL, MAGNETIC, AND ELECTRICAL PROPERTIES OF Mg SUBSTITUTED Ni-Cu-Cd BULK FERRITES OBTAINED FROM NANOCRYSTALLINE POWDERS. Khan, Md. Shahbaz; ID:, 20MSPHY006F Bulk ceramics with optimized density are highly prioritized over ferrite nanoparticles to fabricate devices for their optimal magnetic saturation, lower coercivity, and anisotropy, enhanced resistance, etc. To achieve such bulk specimen using Ni0.5-yMgyCu0.2Cd0.3Fe2O4 disc and toroid samples are sintered at 1423 K keeping the heating and cooling rate at 10 K and 5 K respectively. In this course, structural as well as theoretical Rietveld analysis, optical, and magnetic dielectric and electrical properties have been analyzed using these bulk samples. XRD has explored structural properties and after that these values have analyzed with the Rietveld refinement procedure and obtained goodness of χ2 (1–2) value and other parameters such as lattice parameters, crystal structures, cation distribution, and maximum entropy mapping. Surface morphology and grain size have examined from the as-grown surface without further polishing and annealing by electron microscopy and revealed a decreasing trend of grain size 6.1 μm to 4.2 μm. UV–Vis spectroscopy characterization ensured optical properties for bulk as well as nanopowders and the band gap has been found in the range of 1.4 to 1.6 eV and is increasing with Mg content. Magnetic hysteresis loop exhibits a less decreasing nature up to y = 0.3 of magnetic saturation along with the Law of Approach to saturation which compiles magnetic anisotropy. The temperature dependent magnetization curves exhibit a sharp decreasing value (i.e. dM/dT minimum) at Curie point, decreasing from 630 K to 505 K with increasing Mg content. At 3 T magnetic field the changes in relative cooling power value have been found in the range 53.82 Jkg-1 to 37.79 Jkg-1 which could be considered as potential for magnetocaloric refrigeration. Impedance spectroscopy and other electrical characterization techniques were also employed to study the material's electrical properties. These measurements revealed that Mg2+ substitution improved the samples' electrical conductivity and dielectric properties. The findings of this research show the possibility of Mg2+ substitution as a strategy for tuning the structure, magnetic and electrical properties show the possibility of MLCI application in Ni-Cu-Cd bulk ferrite. A Master of Science (M.Sc) Thesis in Physics Department at Chittagong University of Engineering and Technology (CUET). 2024-10-28T00:00:00Z http://103.99.128.19:8080/xmlui/handle/123456789/575 EFFECTS OF GAMMA AND NEUTRON IRRADIATIONS ON THE PHYSICAL, MAGNETIC AND ELECTRIC PROPERTIES OF Co-Cu-Cd AND Ni-Cu-Cd NANOFERRITES SALAUDDIN, MD. Irradiation effects on the structural, magnetic and electrical properties obtained by the sol-gel auto combustion synthesized Co0.3Cu0.2Cd0.5Fe2O4 and Ni0.3Cu0.2Cd0.5Fe2O4 nanoparticles by gamma (γ) and neutron irradiations are studied in the present research. The neutron irradiation of the samples has been done through neutrons (1.50X1012 cm-2 s-1 and 6.107×1013 cm-2 s-1 thermal neutron flux) from the TRIGA MARK-II research reactor and gamma irradiation by 64 KCi cylindrical 60Co source at room temperature (with doses of 1 MRad and 3 MRad at a dose rate of 0.1067 MRad/h) [for abstract the texts inside the first bracket may be omitted). XRD results show the stable spinel structure formation of the samples for the irradiation doses. The lattice constant (a0) of the investigated samples has been increased with the increase of irradiation (neutron/gamma) due to the conversion of Fe3+ (0.67 Å) to Fe2+ (0.76 Å). Due to the redistribution of ions, changes in the lattice constant have been found by the irradiation through the results of the XRD and Rietveld refinement process. The saturated magnetization obtained from the VSM is found to changes and further analyzed by LAS. The frequency-dependent characteristics such as dielectric constant, electric modulus, impedance analysis and ac conductivity are inspected for all samples with both types of irradiation process. The electrical modulus spectroscopy ensures the dominant property as electric stiffness for investigated ferrite nanoparticles. Cole-Cole plots for the complex impedance analysis suggest the predominant contribution to conduction was through the grain boundary. In this study, electrical and dielectric properties have been carried out with the influence of gamma and neutron irradiations which can be interpreted by the existing theories. A Master of Phylosophy (M.Phil) Thesis in Physics Department at Chittagong University of Engineering and Technology (CUET). 2024-10-28T00:00:00Z