Phil degree in the Department of Physics, Khulna University of Engineering and Technology, Khulna - 9203, Bangladesh. Mahbub Alam, Department of Physics, Khulna University of Engineering and Technology, for his cooperation and inspiration during this work.
THEORY OF NANOMAGNETISM
4I* ill
SYNTHESIS AND CHARACTERIZATION TECHNIQUES
CHAPTER-JY
RESULTS AND DISCUSSION
CHAPTER-V CONCLUSION
Fig.3.12 Magnetic separation of nuclear energy levels 75 Fig.3.13 Energy level scheme of 57Fe Mössbauer spectroscopy includes. Fig.4.4 Change of lattice parameter with annealing temperature for MgFe 2O. Figure inset. shows the enlarged region around the origin to do the pinching.
List of Tables
List of Symbols
INTRODUCTION
INTRODUCTION
Nanotechnology
There are many ways used to create nanostructured materials, which are usually divided into two main strategies, top-down approach and bottom-up approach. Therefore, the idea of creating artificial substances and materials with unique characteristics using the bottom-up approach is increasingly encouraged for the development of new and multifunctional materials.
Nanomaterials
Quantum size effects and the large surface area of magnetic nanoparticles dramatically change some of the magnetic properties and provide superparamagnetic phenomena and quantum tunneling of magnetization. The deviation of properties of the nanosized materials from those of bulk materials is due to surface effects which depend mainly on the ratio of surface area to volume and particle size, together with the chemical composition and interaction between the particles.
Magnetic Nanoparticles
Biomedical Applications of Nanoscale Magnetic Materials
- Biosensor Applications
- Drug Delivery Systems
- Magnetic Resonance Imaging
- Hyperthermia
- Bio-manipulation
- Multifunctional Nanoparticles in Biomedicine
In recent years, several mechanisms have been used to control the rate of drug release. In recent years, much effort has been directed towards the development of magnetic nanoparticles as contrast agents for MRI.
Spinel Magnesium Ferrite
- Properties of Magnesium Ferrite
- Review of Researches on Synthesis and Characterization of Magnesium Ferrite
1.96] investigated the effects of high energy milling on MgFe2O4. The crystallite size of MgFe204 can be reduced to nanometer range by mechanical treatment and also control the redistribution of cations between tetrahedral and octahedral sites. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) were used for structural investigation of the as-prepared ferrite microspheres.
The Aims and Objectives of the Present Work
The chemical coprecipitation method is known to successfully prepare nanocrystalline spinel ferrites with particle sizes smaller than 50 nm. The spin dynamics of the nanoensemble and their bulk magnetic properties will be studied by field dependence of magnetization measurements.
Outline of the Thesis
The theoretical background, including the fundamentals of magnetism, general information about ferrite nanoparticles, and the synthesis technique, will be presented in Chapter II. The methodology of synthesis samples and characterization techniques is the next part of this task and is presented in chapter III.
General Changes as a Function of Scaling
- Surface Area to Volume Increases
- Particle Size Approaching Characteristic Length Scales
The size of the structures approaches and below these characteristic lengths, the physics changes. Some examples of difficulties inherent in studying systems at these scales are domain size, exchange length, coherence mean free path length of electrons, and wavelength of visible light.
Magnetism in Nanoparticles .1 Origins of Magnetic Domains
- Single Domain Limit
- Magnetization Processes and Thermal Energy Effect
- Superparamagentism
- Superparamagentic Limit
Fig.2.1 Evolution of the magnetic energy with the tilt angle between the easy axis and the magnetization direction. Where K is the effective uniaxial magneto crystalline anisotropy constant per unit volume, 0 is the angle between the magnetization direction and the easy axis of the particle, and V is the volume of the particle.
Basic Concept of Nanoparticles Synthesis 1 Nucleation and Growth
L/ SaüafionConcenation Co
Time
Aggregation Phenomena
The secondary particles resulting from the clustering and coalescence of two or more primary nanocrystallites can be monocrystalline or polycrystalline in nature, depending on the arrangement of the smaller units within each larger structural entity [2.17]. The random clustering of the nanocrystalline units can also yield monocrystalline secondary particles when the aggregation is followed by an internal recrystallization process. However, monocrystalline particles are usually obtained by the oriented attachment of the primary nanocrystallites, which necessitates a continuity of the crystal lattices of the adjacent particles through each shared interface.
Synthesis Methods of the Nanocrystalline Ferrites
- Preparation of Nanostructured Ferrites by Physical Methods
- Preparation of Nanocrystalline Ferrites by Wet Chemical Methods
- Synthesis of Nanocrystalline Ferrites in Aqueous SoLutions
In the mechanical activation process, the average grain size of the ferrite powders can be tuned by changing the grinding time. The spins of the magnetic ions located in the tetrahedral interstices (A) are antiferromagnetically coupled to those of the cations residing in the octahedral sites (B). This imposes some limitations on the use of ferrite nanocrystals in some biological systems that require solubility in aqueous environments.
2.4.2.1.1 The Co-precipitation Method
The nature of the precipitating agent was found to significantly affect the morphology of the ferrite nanopowders synthesized by the co-precipitation method. This is not the case for the nanopowders precipitated in the presence of NH4OH, when the particles are found to be less crystalline and their sizes vary from 2 to 10 nm. It was found that the morphological changes of the as-prepared nanopowders during the annealing process depended on their initial composition.
2.4.2.1.2 The Sot-Gel Method
Regardless of the nature of the oxide product, two types of chemical reactions are usually involved in the sol-gel technique: the hydrolysis of the metal/metalloid precursor and the condensation of the resulting intermediates [2.57]. However, the mechanistic pathways through which the intermediates are converted to the final product are significantly different, being primarily determined by the nature of the groups coordinated to the metal ions. If the coordination sphere of the M cations is saturated, the oxolation reaction proceeds through a nucleophilic substitution mechanism.
2.4.2.1.3 The Hydrothermal / Solvothermal Method
2.4.2.1.4 The Microemulsion Method
Synthesis of Nanocrystalline Ferrites in Non-Aqueous Medium
One of the common characteristics of organic solution techniques is the use of capping agents. The non-aqueous techniques involved in the preparation of nanocrystalline ferrites generally fall into two categories, viz. The hydrolysis of transition metal ions in polyol solutions (ethylene glycol, diethylene glycol or I,2-propanediol) with the formation of binary or mixed nanophase metal oxides is traditionally called the polyol method.
2.4.2.2.2 Thermal Decomposition of Single Molecular Precursors
In addition to the water molecules, other organic compounds resulting from the oxidation of the polyols will thus also be removed during the synthesis process. Several factors, such as the reaction temperature, the metal precursor/polyalcohol molar ratio, the reaction time, and the nature of the noble metal used as a seed in the heterogeneous nucleation of other metals or alloys, were found to play an important role in the size of the resulting metallic nanoparticles [2.76]. Unlike the metals, the presence of a certain amount of water in the reaction mixture is essential for the production of metal oxide nanoparticles through the polyol process.
SYNTHESIS AND CHARACTERIZATION TECHNIQUIES
SYNTHESIS AND CHARACTERIZATION TECHNIQUES A
Synthesis of MgFe204 Nanoparticles
- Materials
- Experimental Procedure
When the reaction was completed, the precipitate was filtered and washed several times using deionized water until the pH of the solution became neutral. The powder was pelletized and heated in a box furnace at different temperatures in the range from 200 °C to 1400 °C.
X-Ray Diffraction
- Interpretation of the XRD data
- Determination of Nanometric Grain Size by X-ray Diffraction
In the equation, is the wavelength of the X-ray, 9 is the scattering angle, and n is an integer representing the order of the diffraction peak. Thin sheets of the samples were fabricated from the alloy bar by rolling the bar. The shape of the sample was used as the same as that of the Debye-Scherrer method sample.
Vibration Sample Magnetometer
The voltage induced in the pickup coil increases and detects the lock in the VSM detection module. The VSM sensing module uses the position encoder signal as a reference for synchronous sensing. This encoder signal is obtained from the VSM motor module, which interprets the raw encoder signals from the VSM linear motor transport.
SQUID Magnetometer
Consequently, the magnetic moment of the sample induces an electric current in the pickup coil system. Consequently, the magnetic moment of the sample induces an electric current in the pickup coil system. The magnetic moment of the sample creates a flux in the detection coil, which changes with the sample position.
Mössbauer Spectroscopy
- Mössbauer Effect
- Electric Quadrupole Splitting
- Magnetic Hyperfine Interaction
In a Mössbauer spectrum, the isomer shift is the velocity of the center of gravity of . The valence electrons of the MOssbauer atoms and the asymmetry in the electronic structure contribute to the EFG and this is known as the valence contributions. The magnitude of the separation, Delta, is related to the nuclear quadrupole moment, Q, and the principal component of the EFG, V, by the relation
Experimental Procedure for Mössbauer Spectrometer
If the relative velocity of the source towards the absorber increases, Doppler shift 'y-rays can be made to match resonance conditions with the split levels in the absorber. By changing the velocity of the source, resonance conditions can be obtained for each of the different transitions in the absorber. Several pieces of electronic equipment are used to control the movement of the source and correlate it with the signal from the detector.
Nuclear Magnetic Resonance Spectroscopy
- Basic Principle of NMR
- NMIR Signal Processing
- Relaxation Mode
- Longitudinal relaxation or Ti - recovery
- Transverse relaxation or T2-decay
- NMR Instrumentation
The adsorption process in NMR involves atomic nuclei absorbing electromagnetic radiation in the radio frequency region when placed in an intense external magnetic field. In the presence of an external magnetic field, a nucleus can absorb electromagnetic radiation of the appropriate frequency and undergo a transition between two energy states. From this equation it can be seen that the ratio of the number of spins in the lowest energy level to the number in the upper level depends on the temperature.
RESULTS AND DISCUSSION
I LJL
Magnetic Properties
The inset of the figure shows an enlarged region around the origin to make the low-temperature buckling more visible. One of the remarkable characteristics in M (H) rings is that the magnetization value is high at low temperature, but does not saturate, even at such a high applied magnetic field of 60 kOe. The reason for the high coercivity at low temperature can be understood by considering the effects of thermal fluctuations of the trapped moment along the anisotropy barrier.
Effects of Annealing Temperature on the Magnetic Properties To understand the magnetic properties for different annealing temperatures
The saturation magnetization values (Ms) and coercivity (He) values for the nanoparticles were calculated from the hysteresis curve are shown in Fig. respectively. 4.10 and Fig. 4.l 1.
CM 4.3 Mössbauer Study
In the case of Mossbauer measurements, we investigate the change of the spectrum as a function of temperature, where the onset of superparamagnetism is marked by the change of the Mössbauer pattern from a sextet to a doublet. In the figures below, the outer sextets correspond to Fe ions in the octahedral position, and the inner sextets correspond to the Fe3 ions in the tetrahedral position. This is because as particle size increases, surface area decreases, grain boundaries become smaller, and energy distribution decreases.
III]
NMR Study of Coated Magnesium Ferrite
This shortens the T2 relaxation time due to the creation of a greater homogeneity of the local field in the presence of the contrast agent and thus provides an opportunity to obtain the T2-weighted image [4.14]. Where i=2, C is the concentration of contrast agent, T2 is the relaxation time observed in the presence of contrast agent and T2,0 is the relaxation time in the absence of contrast agent. In the equation above, the contrast agent coefficient called relaxation is a concentration-independent term and indicates the strength of the contrast agent.
The image was obtained in vitro using the phantom, which was designed by filling MgFe 2 O 4 nanoparticle solution of 1.01 mM inside the small tubes, which were inserted into the large tube containing water. The degree of darkening showed that the chitosan-coated MgFe204 nanoparticle solution is suitable for T2 contrast agent. In Fig.4.14 (b), the value of the relaxation time T2 or the relaxation r2 = has been determined and presented in the figure with a scale bar.
CONCLUSIONS
Conclusions
We have verified tuning on the magnetic properties of magnesium ferrite nanocrystals by an appropriate control of both composition and crystal size at the nanoscale. The width of the peaks gave the average crystallite size of nanoparticles using the Scherrer formula. The coercivity of the nano-level samples is almost zero, suggesting superparamagnetic behavior at room temperature.
Suggestions for future work
Brown; Relaxation Measurements of Magnetic Nanoparticles: Towards the Development of a Novel Biosensor System - Licentiate Thesis, Chalmers University of Technology, Gothenburg, 2007. 2.6] Johansson, C.; Magnetic studies of magnetic fluids - Doctoral thesis, Chalmers University of Technology and University of Gothenburg Fannin P. W.; Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing; Academic Press, Inc.: San Diego, p.
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