Therefore, in the light of the above discussion, I strongly recommend that the thesis presented by Ms. A small part of the thesis also deals with the effect of substitution of rare earth ions.
Contents
Introduction
Theoretical Aspects
Results and Discussion of Co1 CdFe204 Ferrites
Introduction
List of Tables
CHAPTER-I Introduction
Introduction
The magnetic properties of ferrites depend on the type of magnetic ions present at the A and B sites and the relative strength of the inter- (JAB) and intra-sublattice (JBB, JAA) interactions. Recently, it has been discovered that the rare earth oxides exhibit important modifications for the improvement of the properties of ferrites.
The Aim and Objectives of the Present Work
A rare earth element (RE) with large magnetic moments, large magnetocrystalline anisotropy, and low-temperature magnetostriction due to its 4f orbital, which is fully shielded by 5s and 5p orbitals, plays an important role in deciding the electrical and magnetic properties of ferrites, as it interacts with 3d electrons of transition metals [1.53]. It has a memory effect, i.e. remember your space and position according to the temperature fluctuation.
The main objectives of the present research work are
- Reason for Choosing this Research Work
- Findings of this Work
- Review Work
- Outiine of the Thesis
- Introduction to Magnetism .1 Magnetic Materials
- The Basis of Magnetism
- Electron Spin
- Magnetic Dipole
- Magnetic Field
- Magnetic Moment
- Magnetization Process
- Magnetic Flux and Flux Density
- Origin of Magnetic Moments
- Magnetic Properties of Solid
- Magnetic Domain and Domain Wail Motion
Above x = 0.8, the reduction of the B-B interaction increases the magnetic moment due to the spin effect. If such a material is placed in an external field, eg, the field created by an electromagnet, the individual atoms will tend to align their fields with the external one.
The average magnetic induction of a ferromagnetic material is closely related to the domain structure. Once the domain growth is complete, a further increase in the magnetic field causes the domains to rotate and align parallel to the applied field.
- Magneto Static or Demagnetization Energy
- Magnetocrystalljne Anisotropy Energy
- Magnetostriction
- Hysteresis
- Magnetization and Temperature
- Theory of Permeability
- Types of Magnetism
- Diamagnetism
- Paramagnetism
Retentivity, a measure of the residual flux density corresponding to the saturation induction of a magnetic material. The delay is caused due to the presence of various losses and is therefore expressed as. where ö is the phase angle and denotes the delay of B with respect to H. The permeability is then given by
TTTTTT T 1
TTTTTTT
TMUT
Antiferromagnetism
In the simplest case, adjacent magnetic moments are equal in magnitude and opposite, so there is no total magnetization involved. The antiferromagnetic susceptibility follows the Curie-Weiss law with negative 0, as does the inverse susceptibility as a function of temperature shown in the figure.
Ferrimagnitism
Antiferromagnetic material with adjacent magnetic moments parallel to each other without an applied field. The natural state makes it different for the material to be magnetized in the direction of the applied field, but still shows a relative permeability slightly greater than above a critical temperature known as the Neel temperature, the material becomes paramagnetic [2.11].
Classification of Ferrites
- Soft Ferrite
- Hard Ferrite
- Cubic Ferrite of Spinel Type
The crystal structure of ferrite is based on a face-centered cubic lattice of the oxygen ions. Variation of cation distribution between the cationic sites leads to different electrical and magnetic properties, even though the composition of the spinel is the same.
Cation Distribution in Ferrites
- Normal Spine! Structure
- Inverse Spinel Structure
- Intermediate Structure
The cations with the smallest positive charge are at the B sites with six anions in the surroundings, i.e.
Magnetic Exchange Interaction
- Superexchange Interaction
- Neel's Collinear Model of Ferrimagnitism
- Non-Collinear Model of Ferrimagnitism
- Re-entrant Spin-Glass Behavior
- Spin-Glass Behavior
The magnetic properties of spinel ferrites are governed by the type of magnetic ions located at the A and B sites and the relative strengths of inter-sublattice (JAB) and intra-sublattice (JAA, JBB) exchange interactions. The magnetic structure of such crystals essentially depends on the type of magnetic ions located at the A and B sites and the relative strength of inter- (JAB) and intra-sublattice exchanges (J, J88). At low temperature compared to J, energy dominates over entropy and the spins of the system are predominantly aligned in the same direction, i.e.
The non-equilibrium character can be observed experimentally from an age dependence of the magnetic response.
Transport Properties
- Conduction Mechanism in Ferrites
- Hopping Model of Electrons
The SG phase is also susceptible to any perturbation in the form of temperature or field changes, which in turn, if large enough, effectively re-initialize the aging process (temperature chaos). The aging behavior and chaotic nature of the low-temperature SG phase were first considered as an additional problem in understanding SO. The temperature dependence of the conductivity arises only from the mobility and not from the number of charge carriers in the sample.
The appearance of n-p transitions with charge carriers in the concentration of Fe2 or oxygen in the system.
Sample Preparation .1 Composition of Ferrites
- Preparing a Mixture of Materials
- Pre-firing the Mixture to form Ferrite at Wet Milling
- Pre-sintering
- Sintering
- Method of Sample Preparation .1 Solid State Reaction Method
As far as the final composition of the ferrite is concerned, step (2) is the most crucial because further steps would not significantly change the composition. The thermodynamic driving force is the reduction of the specific surface area of the particles. Strict control of furnace temperature and atmosphere is very important because these variables significantly affect the magnetic properties of the product.
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.
X-ray Diffraction (XiRD) Technique
- Different Parts of the PHILIPS X' Pert PRO XRD System
- Interpretation of the XRD data
- X-ray Density and Bulk Density
- Porosity
- Permeability Measurement .1 Curie temperature
- Measurement of Curie Temperature by Observing the Variation of Initial Permeability with Temperature
- Permeability
- Mechanisms of Permeability
- Frequency Characteristic of Ferrite Samples
- Low Field Hysteresisgraph
The bulk density was calculated from the cylindrical pellet with the mass (m) and volume (V) of the pellets using the ratio. If we divide this value L0 (inductance of the coil without core material), we get the permeability of the core, i.e. The sample was kept exactly in the middle part of the cylindrical oven in order to reduce the temperature gradient.
Here p is the permeability of the vacuum, N is the number of turns (here N = 5), S is the cross-.
1-11 Bipolar power
- Measurement of an Initial B-H Curve
- AC B-H Curve Measurement
- Materials Geometry
- DC Measurement
- Magnetization Measurement
- SQUID Magnetometer
- The Features of MPMS XL SQUID Magnetometer
- RSO measurements can be made in one of two configurations: Centre or maximum slope. Center scans use large oscillations (2 to 3 cm) around the center point of the
- Extended Low Temperature Capability
- Reciprocating Sample Measurement System Features
- Continuous Low Temperature Control and Enhanced Therinometry
- Configuration
- Measurement Consideration
- Transport Property .1 DC and AC Resistivity
Consequently, the magnetic moment of the sample induces an electric current in the pickup coil system. As the sample moves through the coils, MPMS MultiVu measures the SQUID's response to the sample's magnetic moment. Consequently, the magnetic moment of the sample induces an electric current in the pickup coil system.
Resistivity is an intrinsic property of a material. The technical importance of ferrites lies mainly in their high resistivity.
CHAPTER-IV
Results and Discussion of Co1..CdFe204 Ferrites
Introduction
- Lattice Parameter
- Density
- Temperature Dependence of Initial Permeability
- Compositional Dependence of Curie Temperature
- Frequency Dependence of Initial Permeability
- Low Field B-H loop at Room Temperature
Therefore, single-phase spinel structure is confirmed for all the samples with an increasing trend for the lattice parameter as the Cd content increases. The temperature corresponding to the peak value of dp/dT has been taken as the Curie temperature of the sample. A linear fit of the Curie temperature with x gives an empirical relation for the samples as, T (x) = T x, where T (0) is the Curie temperature of the pure Coferrite and T (x) corresponds to the Curie. temperature of any composition with Cd concentration (x).
The hysteresis behavior and initial permeability reveal the softer ferromagnetic nature of the studied materials with the increase in Cd content.
- Electrical Transport Property
- Compositional Dependence of DC Electrical Resistivity
- Frequency Dependence of AC Resistivity
- Frequency Dependence of Dielectric Constant
- Summary
It has been found that the resistivity decreases with further addition of Cd content. This decrease in resistivity can be attributed to the trapped intragranular porosity, Sankpal et.al. The resistivity of the ferrites is expected to decrease with an increase in frequency; this may be due to the low dielectric constant and also depends on the porosity and composition [4.41]. The increase in permeability can be attributed to the presence of Cd ions that activate the sintering process in ferrites and lead to an increase in density and grain size.
It is found that the DC electrical resistance increases with the increase of Cd content, which is attributed to the fact that the incorporation of Cd into the B-site of ferrite can decrease the concentration of Fe 2'/Fe 31 ion pairs.
CHAPTER-V
Results and Discussion of Coi ZnFe2O4 Ferrites
X-ray Diffraction Analysis .1 Phase Analysis
- Lattice Parameter
- Frequency Dependence of Initial Permeability
- Low Field B-H loop at Room Temperature
- Magnetization Measurement
- DC Electrical Resistivity
The bulk density increases significantly with increasing Zn content indicating improved densification through the substitution of Zn for Co in the ferrite. According to the relationship, increase in i' with Zn content is attributed to the increase in Me with increasing Zn content and may also be due to decrease in K1. It is observed that the saturation magnetization M and nB increases with the increase of Zn content up to x = 0.5 and then decreases.
DC resistivity (Pdc) of Co1ZnFe2O4 ferrites measured at room temperature is presented as a function of Zn content in Fig.
Summary
CHAPTER-VI
RESULTS AND DISCUSSION OF DILUTE FERRITES
Results and Discussion of Dilute Ferrites
- Introduction
- Field cooled (MFc) and Zero field cooled (MzFc) Magnetization
- High field Hysteresis behavior
- Temperature and Frequency Dependence of Complex AC Susceptibility
- Ageing, Rejuvenation and Memory Effects
- Summary
Spin-glass-like behavior with the manifestation of a sharp peak at low temperature from the temperature dependence of low-field dc magnetization with H = 50 Oe is shown in Fig. to study. Frequency-dependent complex AC susceptibility and DC magnetization measurement reveal that the sample exhibits spin-glass behavior.
The samples show typical spun glass behavior (PM-SG) with the manifestation of non-equilibrium dynamics of the spun glass such as aging, rejuvenation and memory effects.
RESULTS AND DISCUSSION OF
Results and Discussion of Rare-earth Substitution in
Introduction
It is clearly observed that the undoped samples show the formation of a single-phase cubic spinel structure without an additional peak, as shown in Figure 7.1, while all the RE-doped samples show additional peaks that are not spinel and probably correspond to the second phase of REFe03 (orthoferrites). shown in the figure Determining the exact phase was not possible, as the number of additional peaks other than spinel is not sufficient for accurate analysis. It was previously reported that RE-doped ferrites have additional crystalline phases due to their low solubility [7.12].
The formation of a secondary phase may be the result of the diffusion of some Ho3 ions having an ionic radius greater than that of Fe3 during the sintering process to the grain boundaries, while rare earth ions having a smaller size may enter in the spinel lattice forming a single phase. .
Temperature Dependence of Magnetization (MZFC and MFC)
From the dMIdT it appears that T = 100 K may be the T of this composition, i.e. the sample is ferrimagnetic below T which was also verified with the appearance of spontaneous magnetization from the Arrott plots drawn from the high field (M-H) data at T = 5 - 100 K (Fig. 6.2.c). It is clearly observed that temperature corresponding to ' does not shift with frequency and that the. No ferromagnetic phase transition above the spin freezing temperature as in the case of undoped samples with I = lOOK was observed.
It is observed that, like undoped samples, M(T) measurement shows no clear magnetic phase transition, but M(T) is very similar to undoped samples (Fig. 6.3. a).
High field Magnetic Hysteresis
Coercive field H = 690 Oe for undoped CoO2Zn08Fe2O4 sample at T = 5K, which increases significantly for the Gd-doped samples and slightly for Eu-doped samples. It is worth mentioning that the magnetization increased significantly for the Gd3-doped samples, while it decreased slightly for Eu-doped samples. The magnetization enhancement at T = 5K for the Gd3 doping sample is likely due to the high magnetic moment of the Gd 31 free ion of 7.8 PB and that higher Gd3 doping has a higher magnetization of 82.58 emu !gm compared to 64.51 emulg for the undoped samples.
The decrease in magnetization for Eu doping is due to the non-magnetic nature of Eu, which does not have the magnetic moment of the Eu3 free ion even at low temperature.
Summary
Conclusion
