Tailoring of structural and magnetic properties of nanosized lithium ferrites synthesized by sol-gel self-combustion method (original) (raw)
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The ultra fine particles of the cobalt substituted lithium ferrites with the formula [Li 0.5 Fe 0.5 ] 1 À x Co x Fe 2 O 4 (0.0r x r 1.0) were synthesized by low temperature citrate-gel auto combustion method. Structural characterization of the samples was carried out using XRD studies and FESEM (Field Emission Scanning Electron Microscopy) analysis. XRD studies confirms the formation of single phased spinel structure with crystallite size in the range of 36–43 nm. The M–H loops have been traced using Vibrating Sample Magnetometer (VSM) for all the compositions at room temperature and hysteresis parameters were evaluated. The hysteresis loops of the prepared samples show clear saturation at an applied field of 720 k Oe and the loops were highly symmetric in nature. The dielectric parameters such as dielectric constant (ε'), dielectric loss tangent (tan δ) of the samples were studied as a function of frequency in the range of 20 Hz to 2 MHz at room temperature using LCR Meter. The dielectric constant and loss tangent of the samples show a normal dielectric behavior with frequency which reveals that the dispersion is due to the Maxwell-Wagner type interfacial polarization and hopping of electrons between the Fe 2 þ and Fe 3 þ ions.
Physica B-condensed Matter, 2009
Lithium ferrite has been considered as one of the highly strategic magnetic material. Nano-crystalline Li 0.5 Fe 2.5 O 4 was prepared by four different techniques and characterized by X-ray diffraction, vibrating sample magnetometer (VSM), transmission electron microscope (TEM) and Fourier transform infrareds (FTIR). The effect of annealing temperature (700, 900 and 1050 1C) on microstructure has been correlated to the magnetic properties. From X-ray diffraction patterns, it is confirmed that the pure phase of lithium ferrite began to form at 900 1C annealing. The particle size of as-prepared lithium ferrite was observed around 40, 31, 22 and 93 nm prepared by flash combustion, sol-gel, citrate precursor and standard ceramic technique, respectively. Lithium ferrite prepared by citrate precursor method shows a maximum saturation magnetization 67.6 emu/g at 5 KOe.
Cobalt substituted Lithium Nano ferrites with the chemical composition [Li 0.5 Fe 0.5 ] 1 À x Co x Fe 2 O 4 (where x ¼0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized through Citrate-Gel auto combustion technique. Structural characterization of the prepared ferrites was carried by X-ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM). XRD analysis has confirmed the formation cubic spinel structure of the ferrite compositions with a particle size ranging from 37 nm to 42 nm. The SEM images represent large agglomeration of the nano particles of the ferrite samples with broader grain size distribution. Temperature dependent magnetic properties of [Li 0.5 Fe 0.5 ] 1 À x Co x Fe 2 O 4 for two compositions with cobalt content x ¼0.8 and x ¼ 1.0 were carried out using Vibrating sample magnetometer (VSM). The magnetization as a function of an applied field 7 10 T was carried out at temperatures 5 K and 310 K. Field cooled (FC) and Zero field cooled (ZFC) magnetization measurements under an applied field of 100 Oe and 1 KOe in the temperature range of 5-375 K were performed. These measurements have resulted the blocking temperature (T b ) at around 350 K i.e. above room temperature for both the ferrites. Below this temperature the ferrites show ferromagnetic behavior and above which superparamagnetic behavior where the coercivity and remanence magnetization are almost zero. Such behavior makes the ferrites to be desirable for biomedical applications.
The structural and magnetic properties of lithium ferrite nanoparticles synthesized through the solution combustion route at different fuel to oxidizer ratio are studied using different techniques. Powder X-ray diffraction studies show that the fuel to oxidizer ratio is a critical parameter that determines the phase purity and degree of order of the samples. Magnetic studies show that the saturation magnetization and coercivity are comparable to those reported for lithium ferrites prepared using other methods. Saturation magnetization of Li0.8 sample at room temperature is 60 emu/g and is close to the bulk value. The hyper-fine parameters obtained from the Mössbauer spectra of Li0.6 and Li0.8 also match the reported values of phase pure samples. Mössbauer spectra of samples prepared at stoichiometric and fuel rich conditions show the presence of Fe 2+ cations in the ferrite phase, indicating that a reducing environment which reduces Fe 3+ to Fe 2+ ions is created as the fuel to oxidizer ratio is increased. The variation in the structural and magnetic properties of the samples, combined with TGA and FTIR studies, shows that the fuel lean condition is more appropriate for the direct formation of single phase lithium ferrite nanoparticles.
Applied Nanoscience, 2021
In this study, we report the synthesis of nanosized Al-substituted lithium–iron ferrites Li 0.5 Al x Fe 2.5- x O 4 (0 ≤ x ≤ 1) by sol–gel auto-combustion method and by ceramic method with double sintering. Synthesized materials were studied using X-ray diffraction and impedance spectroscopy. The samples obtained by chemical methods have a higher homogeneity of the distribution of elements by volume, good repeatability of the result, high crystallinity, small crystallite size and perfect stoichiometry. Based on Koop's theory, the basic regularities of the behavior of the dielectric constant and the loss tangent are explained. The jump mechanism of conductivity has been realized by the transition of an electron between iron ions in different valence states. Samples synthesized by the sol–gel auto-combustion show technological characteristics, compared with systems obtained by solid-phase method.
Magnetic Properties of Lithium Ferrite Nanoparticles with a Core/Shell Structure
Current Nanoscience, 2012
We present a magnetic study of lithium ferrite nanoparticles of composition Li0.5Fe2.5O4, synthesized by a citrate gel decomposition method. The as prepared sample was composed of nearly spherical nanoparticles with an average particle size TEM~12 nm. Further annealing at 573 K and 673 K for 4 hours did not increase particle size noticeably, while annealing at 973 K led to morphology changes and significant increase in size ranging from 40 to above 200 nm. The magnetic properties of samples have been studied using Mössbauer specroscopy, and static magnetic measurements. The hyperfine parameters obtained from Mössbauer data at T = 10 K are in agreement to the bulk lithium ferrite phase. Annealed samples showed an evolution from monodomain structure to polycrystalline behaviour, what is evident from TEM imagines, as well as the evolution of the coercive filed, HC, and the saturation magnetization, MS, with particle size increase. The exchange interactions have been observed in the single domain nanoparticles, which probably originate from their core shell structure. At low temperatures and in high enough magnetic fields, the cubic magnetic anisotropy stays preserved and the magnetic moments in the particle core are aligned along 111 directions of the spinel structure.
Applied Physics A, 2017
This paper has been dedicated to the synthesis and characterization of a series of lithium-substituted cobalt ferrites Li x Co 1-x Fe 2 O 4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1). These samples have been prepared using simple ball milling machine through powder metallurgy route. The structural analysis is carried out using X-ray diffractometer and their 3D vitalization is simulated using diamond software. The frequency and temperature-dependent dielectric properties of prepared samples have been measured using inductor capacitor resistor (LCR) meter. The structural analysis confirms that all the prepared samples have inverse cubic spinel structure. It is also revealed that the crystallite size and lattice parameter decrease with the increasing concentration of lithium (Li ?1) ions, it is due to the smaller ionic radii of lithium ions. The comprehensive analysis of frequency, concentration and temperature-dependent dielectric properties of prepared samples is described in this paper. It is observed that the dielectric constant and tangent loss have decreased and conductivity increased as the frequency increases. It is also revealed that the dielectric constant, tangent loss and AC conductivity increase as the concentration of lithium increases due to its lower electronegativity value. Temperature plays a vital role in enhancing the dielectric constant, tangent loss and AC conductivity because the mobility of ions increases as the temperature increases.
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2010
Cobalt doped lithium ferrite nanoparticles were synthesized at different pH by sol-gel method. The effect of pH on the physical properties of cobalt doped lithium ferrite nanoparticles has been investigated. The nanoparticles synthesized at different pH were characterized through X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectroscopy (RS), Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and vibrating sample magnetometer (VSM). The XRD patterns were analyzed to determine the crystal phase of cobalt doped lithium ferrites nanoparticles synthesized at different pH. The XRD results show the formation of impurity free cobalt doped lithium ferrites having ordered phase spinel structure. A similar kind of conclusion was also drawn through the analysis of Raman spectra of the nanoparticles synthesized at different pH. SEM micrographs show that the structural morphology of the nanoparticles is highly sensitive to the pH during the synthesis process. The magnetic properties such as; saturation magnetization (Ms), remnant magnetization (Mr) and coercivety (Hc) have been also investigated and found to be different for the nanoparticles synthesized at different pH, which may be attributed to the different size and surface morphology of the nanoparticles.
Vietnam Journal of Chemistry, 2017
In this work, we present a structural, morphology and magnetic study of the Li 0.5 Fe 2.5-x Cr x O 4 spinel nanoparticles (x = 0, 0.5, 0.75, 1, and 1.25) with mean particle size of 20-30 nm prepared by sol-gel method. The lattice constants and the size of particle decrease with increasing Cr concentration. In these samples, the preference of Cr 3+ and Li + ions in the octahedral sites and a small degree of site-interchange between Li + in the octahedral sites and Fe 3+ in the tetrahedral sites were found which increases with increasing the Cr content. A decrease of magnetization due to the spin disorder in the surface layer of the particles was observed. The spontaneous magnetization at 5K suggests the Néel type of magnetic ordering in these samples. The magnetic coercivity is discussed in terms of particle size, morphology and chromium substitution.
Journal of Magnetism and Magnetic Materials, 2011
Sintering temperature and particle size dependent structural and magnetic properties of lithium ferrite (Li0.5Fe2.5O4) were synthesized and sintered at four different temperatures ranging from 875 to 1475 K in the step of 200 K. The sample sintered at 875 K was also treated for four different sintering times ranging from 4 to 16 h. Samples sintered at 1475 K have the cubic spinel structure with a small amount of α-Fe2O3 (hematite) and γ-Fe2O3 (maghemite). The samples sintered at≤1275 K do not show hematite and maghemite phases and the crystals form the single phase spinel structure with the cation ordering on octahedral sites. Particle size of lithium ferrite is in the range of 13–45 nm, and is depend on the sintering temperature and sintering time. The saturation magnetization increased from 45 to 76 emu/g and coercivity decreases from 151 to 139 Oe with an increase in particle size. Magnetization temperature curve recorded in ZFC and FC modes in an external magnetic field of 100 Oe. Typical blocking effects are observed below about 244 K. The dielectric constant increases with an increase in sintering temperature and particle size.► Lithium ferrite with heat treatment. ► Structure changes from disordered system to ordered system. ► Magnetization increases with sintering temperature. ► Blocking temperature increases with sintering temperature. ► Coercivity decreases with sintering temperature.