Shibendra Shekher Sikder, Department of Physics, Khulna University of Engineering and Technology (KUET) for his indispensable guidance, keen interest, constructive suggestions, fruitful discussion and constant inspiration throughout the research work. Abdullah Elias Akhter, Head, Department of Physics, Khulna University of Engineering and Technology (KUET) for his strong support in various ways throughout the period of my study in this department.
Contents
Experimental Procedure for Mössbauer Spectrometer 79
CHAPTER- V Conclusions
Chapter-I Introduction
- Introduction
- The Aims and Objectives of the Present Work
- Reason for Choosing this Research Work
- Review Works
- Outline of the Thesis
Since the relaxation time is sensitive to volume [1,9], the Mossbauer spectrum is the sum of spectra with different relaxation times. The isomer shifts indicated that the iron ions were ferrite at the tetrahedral (A) and octahedral sites (B). The quadrapole shifts showed that the orientation of the magnetic hyperfine field relative to the principal axes of the electric field gradient was random.
Chapter-Il Theoretical Background
Origin of Magnetism
- Diamagnetism
- Paramagnetism
- Ferromagnetism
- Antiferromagnetism
- Ferrimagnitism
In the absence of an applied magnetic field, the dipole moments are randomly oriented; therefore, the materials have no net macroscopic magnetization. Paramagnets do not retain any magnetization in the absence of an external magnetic field.
Classification of Ferrites and its Relevance
- Soft Magnetic Materials
- Soft Ferrites
- Hard Ferrites
- Cubic Ferrite with Spinel Structure
- Cation Distribution in spinels
- Normal Spinel Structure
- Inverse Spinel Structure
- Intermediate Structure
These are characterized by low coercive forces and high magnetic permeability. The low coercivity means that the materials' magnetization can easily change direction without dissipating much energy (hysteresis losses), while the materials' high resistance prevents eddy currents in the core, another source of energy loss. generally exhibit small hysteresis losses. The crystal structure of ferrite is based on a cubic lattice of face-centered oxygen ions.
Magnetic properties of Ferrites
- Magnetic Dipole
- Magnetic Field
- Magnetic Moment
- Magnetic Moments of Ferrites
The strength of the magnetic field it produces at any point is proportional to the magnitude of its magnetic moment. The saturated magnetic moments of some selected spinels [2.24] are listed in table (2. 1), the first six ferrites are of the inverse type, i.e. Fe3 [Me2 Fe3 ]O4.
Magnetic Exchange Interaction
IV 2.4.1 Superexchange Interaction
- Neel's Collinear Model of Ferrites
- Non-Collinear Model of Ferrimagnitism
- Initial Permeability of Ferrites
- Theories of Permeability
- Magnetization Processes
- Magnetization Curve
- Magnetization and Temperature
- Hysteresis
In the second stage magnetization curve, if the field is increased, the intensity of magnetization increases more drastically, called the irreversible magnetization region. The reverse magnetization force has reversed enough of the domains so that the net flux in the material is zero.). The force required to remove the residual magnetism from the material is called the coercive force (He) or coercive force of the material.
Note that the curve did not return to the origin of the graph because some force is required to remove the residual magnetism.
Mössbauer Effect
These zero-phonon gamma transitions take place between the excited and ground state nuclear energy levels of the nucleus, which is bound in a solid matrix as reported by Mössbauer [2.37]. The frequency spread of such transitions, which occur between nuclear excited states, is solely determined by the energy uncertainty of the nuclear excited state involved. The important parameters that can be measured using Mössbauer spectroscopy describe the interaction of the nucleus with the surrounding atomic electrons.
The Hamiltonian for the interaction between the core and the surrounding changes can be written as [2.38].
Velocity (mrn/s)
- Isomer Shifts
- Electric Quadruple Splitting
- Magnetic splitting
- Magnetic Hyperfine Interaction
This would cause different shifts in the energy of the 7-rays from source nuclei and absorber nuclei. The valence electrons of the Mossbauer atoms and the asymmetry in the electronic structure contribute to the EFG, known as valence contributions. The positions of the lines are related to the splitting of the energy levels, but the intensities of the lines are related to the angle between the Mössbauer gamma ray and the nuclear torque.
The internal magnetic field in the nucleus originates from the spin and the radial and angular distribution of the electron density in the atom.
Chapter-Ill Experimental Procedure
Methodology of Ferrite Preparation
- Composition of the studied Ferrites System
- Method of Sample preparation
- Synthesis of Co-Cd Ferrites
- Solid State Reaction Method
- Pre-firing the Mixture to form Ferrite at wet milling
- Pre-sintering the Mixture to form Ferrite
- Converting the ferrites into powder and pressing the powder
- Sintering
This means that ferrites achieve their homogeneous composition through solid state reactions and that the shapes of the ferrite products are produced by pressing and then sintering. The extent of this work in this step varies greatly depending on the starting materials. When component oxides are used, the corresponding step merely involves mixing the oxides by wet milling. The thermodynamic driving force is the reduction of the specific surface area of the particles.
Strict control of oven temperature and atmosphere is very important because these variables have significant effects on the magnetic properties of the product.
Why do need Sintering?
- X-ray Diffraction (XRD)
- Different Parts of the PHILIPS X' Pert PRO XRD System
- Interpretation of the XRD data
- X-ray Density and Bulk Density
- Porosity
- Permeability Measurement
- Agilent Precision Impedance Analyzer (Agilent, 4192A)
- Curie Temperature
- Measurement of Curie temperature by observing the Variation of Initial Permeability with Temperature
- Mechanisms of Permeability
- Techniques of Measurements of Permeability
- Frequency Characteristics of Ferrite Samples
- Magnetization measurement
- Vibrating Sample Magnetometer (VSM)
- Principle of VSM
- Experimental Procedure for Mössbauer Spectrometer .1 Instrumentation
The mass density was calculated considering a cylindrical pellet of mass (m) and volume (V) of the pellets using the relation. By dividing this value by L0 (inductance of the coil without core material), we got the permeability of the core, ie the sample was kept only in the middle part of the cylindrical furnace to minimize the temperature gradient.
A small portion (10-50 mg) was weighed and made to avoid movement inside the sample holder.
Drive
Velocity Drive System
To provide a Doppler motion to the source relative to a stationary observer or vice versa, a velocity drive system is used. Triangular wave is fed as a reference signal to one of the transducer coils which acts as a pick up coil. Also due to transducer motion, a signal is induced at this pick-up coil that subtracts from the reference, generating an error signal which is amplified, integrated, and then fed to a complementary circuit to push-pull power amplifier that drives the coil.
Impulses with a repetition rate equal to the frequency of a triangular wave formed from the leading edge of the square wave obtained by differentiation of the triangular wave.
The electrons will accelerate towards the anode and form other ion pairs by collision with the gas atoms. Multiplication factors as high as 105 can be obtained, and the anode current will be proportional to the -y-ray energy. The solid state detector has extremely good energy resolution (600Ev at 14.4keV), but it cooled down below 1200k.
For 14.4KeV y-rays, a proportional counter gives good performance with a high efficiency and a reasonably good resolution.
Pre-amplifier and Amplifier
Single Channel Analyzer
Data Storage system
Synchronization must be maintained between the amplitude of the drive speed and the channel number of the MCA. The first set of 256 channels belongs to positive Doppler velocities and the second set of remaining 256 channels, which is the mirror image of the first, belongs to negative Doppler velocities.
Description of work done
Calibration of 57Fe absorber sample for measurement of Mössbauer parameters
Therefore, to match the source energy to each of the six allowed energy differences, in ferrous metal absorbers; one must give six different speeds to the source.
Computer Analysis of the Data
The purpose of this thesis is to investigate in detail the effects of substitution of Cd 21 ions, covering a wide concentration range, on the structural, magnetic properties and Mossbauer spectroscopic analyzes of Co Fe204 ferrites. When magnetic dilution of the sublattices is introduced by substituting non-magnetic ions in the lattice, frustration and/or disorder occurs, leading to the collapse of the collinearity of the ferromagnetic phase by local spin-canting exhibiting a wide spectrum of magnetic order, e.g. . A systematic line broadening effect in the Mössbauer spectra was observed and was interpreted as originating from different Cd ion dependences of the magnetic hyperfine field at different iron sites.
The displacement of the quadrupoles showed that the orientation of the magnetic hyperfine field with respect to the principal axes of the electric field gradient was random.
X-ray Diffraction .1 Phase Analysis
- Density and Porosity
- Temperature Dependence of Initial Permeability
- Compositional dependence of Curie temperature
- Frequency Dependence of Initial Permeability
- Frequency Dependence of Relative Quality Factor
- Variation of Saturation Magnetization at Room Temperature
- Variation of Magnetization with Temperature
Figure 4.8 shows that the higher the permeability, the lower the resonant frequency of the material. It is also observed that the higher the permeability of the material, the lower the frequency of the onset of ferromagnetic resonance. The resonance frequency of Snoek's limit fr' together with the permeability of the samples are shown in Table 4.2.
From fig. -4.12 it is also noted that the relative Q-factor of the samples increases with the increase in Cd content(x).
Experimental Results and Analysis of Mössbauer for Co-Cd Ferrites
Room temperature Mössbauer spectra, typical of Co-Cd ferrites, are obtained and the changes in the spectra corresponding to the different compositions of the system Coi.CdFe204 are shown in Fig- 4.17(a, b, c & d) and Fig-( e, f, g). Small effect on the isomer shift values, indicating that the s- electron change distribution of Fe 3. The EQ of the Fe - atom in the ferrites with the composition CoiCdFe204 is observed in the range -0.8.89 to 0.754 mm/s as shown in Table -4.4 The observed trend for the Mössbauer line broadening and the average quadrupole splitting points to a gradual
The results of the average magnetic hyperfine field (Hhf) of the sample of Co-Cd ferrites with the composition Co1CdFe204 are shown in Table 4.4.
Conclusions
Conclusions
The existence of tilted spin gives rise to the Yafet-Kittle angle (UyK) which compresses the strength of the A-130 and B-B exchange interaction. The increase in Y-K angles for the samples with Cd content (x > 0.4) is attributed to the increased preference for triangular spin arrangement at B sites due to frustration of B-B exchange interaction. The Mössbauer spectra for the samples clearly show Lorentz-shaped lines in a sextet-wide distribution of the magnetic hyperfine field (Hhf) compared to pure 57Fe films up to x = o.5 but x.
The average magnetic Hhf of the Co-Cd ferrites decreases due to the weakening of A-B exchange interaction caused by the replacement of magnetic Co 2 with non-magnetic Cd 2 ions, which also causes a decrease in the Curie temperature results, our observation that the replacement of large Fe 3 ions by smaller Cd +2 ions reduces the influence of the nternal hyperfine field at nei i areste Fe sites by +3 transferred hyperfine field.
Barakat, "Effect of Electron Jump Speed and Jump Length on the Conductivity and Dielectric Properties of Co-Cd Ferrite" J. Barakat "Effect of Electron Jump Speed and Jump Length on the Conductivity and Dielectric Properties of Co-Cd Ferrite "J. 34; Structure and Magnetic Properties of Cd and Ti/Si Substituted Cobalt Ferrites", Materials Chemistry and Physics 57(1998)86.
4.29] Saiduzzaman, “The additives on the physical and magnetic properties of Cu-substituted Ni-Zn ferrites”; Ph.D.
