Standard Ceramic Technique Research Articles

A study of the structural and electrical properties of Ni1-x Cox Fe2O4 ferrites

Ferrite with general formula Ni1-x Cox Fe2O4(where x=0.0.1,0.3,0.5,0.7, and 0.9), were prepared by standard ceramic technique. The main cubic spinel structure phase for all samples was confirmed by x-ray diffraction patterns. The lattice parameter results were (8.256-8.299 °A). Generally, x -ray density increased with the addition of Cobalt and showed value between (5.452-5.538gm/cm3). Atomic Force Microscopy (AFM) showed that the average grain size and surface roughness was decreasing with the increasing cobalt concentration. Scanning Electron Microscopy images show that grains had an irregular distribution and irregular shape. The A.C conductivity was found to increase with the frequency and the addition of Cobalt, D.C conductivity was found to increase with temperature due to decreases in resistivity. Dielectric constants were noticed to decrease with frequency and Co addition. The Hall coefficient was found to be positive. This demonstrates that the majority of charge carriers are p-type, suggesting that the mechanism of conduction is predominantly caused by hopping of holes.

Metamagnetism in manganate magnesium ferrite

Abstract The metamagnetic properties of the manganese magnesium ferrites having the general formula Mn0.7Mg0.3Fe2O4 prepared by the standard ceramic technique have been studied. It is proposed that when a change of temperature at adequate magnetic field is applied in a Mn0.7Mg0.3Fe2O4 a magnetic phase transition will be generated, giving rise to an antiferromagnetic (AFM) state from ferrimagnetic (FM) phase. The critical transition field H ac = 300 A/m was estimated for critical magnetization curve of transition from the metamagnetic behavior to FM behavior of sample. The FM to AFM transition in these ferrites is accompanied by a Néel type to Yafet-Kittel type transition and gradual spin ordering changes of the unit cell volume. The application of an external magnetic field to the low-temperatures AFM state causes the sample to reset to the original FM state.

Effect of sintering regimes on the microstructure and magnetic properties of LiTiZn ferrite ceramics

In present work, the influence of sintering regimes on the microstructure, saturation magnetization, density and porosity, the grain size, the Curie point, and the temperature dependence of the initial permeability of LiTiZn ferrite ceramics was investigated. Ceramics was prepared by a standard ceramic technique. The formation of a single-phase cubic spinel structure was confirmed by XRD analysis. The Curie point was determined from both the temperature dependences of the initial permeability and the method of thermogravimetric measurements in a magnetic field. Density/porosity and the grain size, the Curie point and magnetization are sensitive to the sintering regime. The initial permeability of ferrite decreases with sintering temperature (in the range of 1010–1150 °С) and grain size increasing that contradicts the generally accepted Globus and Smith-Wijn theories. A possible reason of such behavior is the formation of intragranular pores growing with the increase in the sintering temperature and inhibiting the domain wall motion inside the grain. These results correspond to the porosity of the investigated ferrite ceramic samples, which grows with sintering temperature increasing.The non-stoichiometry arising due to evaporation of lithium and zinc oxides at temperature above 1010 °C affects the initial permeability. In this work, a qualitative assessment of the defective state of ferrite samples obtained under various sintering regimes was given.

Preparation and investigation of structure, magnetic and dielectric properties of (BaFe11.9Al0.1O19)1-x - (BaTiO3)x bicomponent ceramics

(BaFe11.9Al0.1O19)1-x - (BaTiO3)x with x = 0, 0.25, 0.5, 0.75 and 1 bicomponent ceramics has been prepared from single-phase compounds of BaFe11.9Al0.1O19 (x = 0) (BFO) and BaTiO3 (x = 1) (BTO) by a standard ceramic technique. The constituent materials have been chosen considering their perspective ferrimagnetic and ferroelectric properties, respectively for BFO and BTO. Moreover, Ba-hexaferrites are reported to exhibit ferroelectricity at room temperature as well, and the combination of two ferroelectric phases is of interest. Systematic investigations of the structural, magnetic and dielectrical properties versus chemical composition (x) have been performed. The ferrimagnetic phase transition temperature is almost independent of the BTO content, which is determined by intensity of the Fe3+-O2--Fe3+ indirect superexchange interactions in the BFO hexaferrite phase. However, the coercivity of composite samples is lower due to the contribution of the microstructure-dependent shape anisotropy to the total magnetic anisotropy energy. The permittivity vs. temperature behavior confirmed the existence of two ferroelectric phase transitions corresponding to structural phase transitions in BTO at ~ 400 K and BFO at ~ 700 K. It has been observed that the dielectrical properties of composite samples, including the temperatures of the phase transitions, critically depended on concentration x which affects the composite microstructure. This behavior has been discussed in terms of microstructure analysis and such parameters as the grain size, porosity and density.

Influence of gamma irradiation and Er3+ substitution on the structure, magnetic and electrical properties of Mn2+ substituted Ni–Zn ferrite

The effect of gamma irradiation and the substitution by Er3+ ions on the microstructure, magnetic and electrical properties was studied for some ferrite samples of the general formula Ni0.1Mn0.5Zn0.4ErxFe2−xO4, (0 ≤ x ≤ 0.1, step 0.025). The samples are prepared using the standard ceramic technique. The structure of the prepared samples is confirmed using x-ray diffraction patterns. The samples are irradiated at a certain dose of 100 kGy using gamma rays of 60Co source. The obtained results show high stability of the crystalline structure where no new phases were found as a result of the high dose of gamma irradiation. The lattice parameter of the prepared samples is found to increase with increasing Er3+ content. The surface morphology of the samples and the percentage of the ions are studied using scanning electron microscope and EDAX analysis respectively. The effect of temperature and substitution by Er3+ ions on the saturation magnetization and initial permeability are also studied. The experimental results indicate that, the substitution by Er3+ ions led to improve the magnetic properties of the studied samples. Also, the obtained results show a decrease in the saturation magnetization and improvement in the coercivity of the samples as a result of gamma irradiation. On the other hand, the present study shows an increase in the DC conductivity due to the substitution by Er3+ ions and gamma irradiation. The final results show that, the sample of x = 0.025 has high magnetic properties and low porosity which can be exploited in a certain technical applications.

Development of Ferrite-Based Temperature Sensors for Magnetic Resonance Imaging: A Study of Cu1−xZnxFe2O4

We investigate the use of Cu1-x Zn x Fe2O4 ferrites (0.60 < x < 0.76) as potential sensors for magnetic- resonance-imaging thermometry. Samples are prepared by a standard ceramic technique. Their structural and magnetic properties are determined using x-ray diffraction, scanning electron microscopy, super-conducting quantum-interference device magnetometry, and Mossbauer and 3-T nuclear-magnetic-resonance spectroscopies. We use the mass magnetization of powdered ferrites and transverse relaxivity r*2 of water protons in Ringer's-solution-based agar gels with embedded micron-sized particles to determine the best composition for magnetic-resonance-imaging (MRI) temperature sensors in the (280-323)-K range. A preclinical 3-T MRI scanner is employed to acquire T*2 weighted temperature-dependent images. The brightness of the MRI images is cross-correlated with the temperature of the phantoms, which allows for a temperature determination with approximately 1°C accuracy. We determine that the composition of 0.65 < x < 0.70 is the most suitable for MRI thermometry near human body temperature.

A Comparative Study of Physical Properties of Er and Yb Nanophase Ferrite for Industrial Application

Nano ferrites CuCr0.3Er0.03Fe1.67O4 and CuCr0.3Yb0.03Fe1.67O4 were synthesized using standard ceramic technique. X-ray diffraction (XRD) patterns confirmed that the samples had cubic spinel structures. The average crystallite sizes of Er and Yb samples were in the range of 104.2–100 nm. The morphology analyses using field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) confirmed that the samples were in the nanoscale range. The compositional analyses using energy-dispersive x-ray (EDX) showed the atomic percentage (at.%) and weight percentage (wt%) of the investigated samples. The magnetic properties were carried out at room (300 K) and at low (100 K) temperatures magnetic hysteresis loop. The data showed that Er sample had higher saturation magnetization (Ms) and lower coercivity (Hc) than that of Yb sample suggesting that Er sample can be applied in magnetic applications. Moreover, Er sample had higher dielectric constant (e’), dielectric loss (e”) and dielectric loss tangent (tan δ) than that of Yb sample. However, Yb sample had higher resistivity than that of Er sample suggesting that Yb sample can be applied in electrical applications.

Laser induced adjustment of the conductivity of rare earth doped Mn-Zn nanoferrite

AbstractTwo series of Mn-Zn nanoferrites (namely Mn1-xZnxFe2O4and Mn1-xZnxFe2-yRyO4) were synthesized using standard ceramic technique. X-ray diffraction and FT-IR were employed in the chacterization of the nanopowder. The X-ray density for each sample increased after laser irradiation which was correlated with the decrease in the unit cell volume. The study involved the thermal and frequency variation of the dielectric constant and AC conductivity of the investigated samples before and after laser irradiation. The later altered the conductivity by decreasing its value for the rare earth doped samples except for the Sm3+doped one. The results suggested the exploitation of Mn-Zn doped rare earth nanoferrites in many technological applications demanding high resistivity.

Influence of La substitutions on the magnetic after-effect in hexaferrites and garnets

Magnetic relaxation has been measured in La-Co substituted M-type Sr hexaferrites and La substituted YIG polycrystalline samples prepared by means of standard ceramic techniques. In the temperature range between 80 and 420 K, the magnetic disaccommodation has been measured. The isochronal disaccommodation spectra show the presence of different relaxation processes. In hexaferrites, the La doping distort the lattice size and the arrangement of cations within the structure, changing the strenght of relaxation processes regarding unsubstituted samples. In garnets, substitution rate only modify lattice size, whereas with CO2 atmosphere the formation of secondary perovskite phase is detectable with this technique.

Structural and electro-magnetic properties of low temperature co-fired BaSrTiO3 and NiCuZn ferrite composites for EMI filter applications

For the application of electro-magnetic interference filter, magneto-electric composites of spinel ferrite (Ni0.25Cu0.20Zn0.55)Fe2O4 and dielectric (Ba0.75Sr0.25)TiO3 have been prepared by a standard ceramic technique and the effects on structural, dielectric and electro-magnetic properties have been investigated. Ferrite-dielectric mixed powder is uniaxially pressed into toroids and pellets. Specimens are sintered at 950 °C. Powder X-ray diffraction (XRD) indicates a mixed phase of composites with spinel and perovskite phase. The microstructural analysis shows dense structure with some porosity. The variations in dielectric constant and loss tangent with frequency are also studied. The dielectric constant of composite continuously decreases and permeability increases with increasing ferrite content. Observations of P–E hysteresis loops and M–H hysteresis loops, respectively, confirm the dielectric and ferromagnetic nature of the composite samples.

Dielectric and magnetoelectric properties of Li-Mg ferrite: Barium titanate composites

The magnetoelectric composites with composition, (y) Li0.45Mg0.1Fe2.45O4 + (1-y) BaTiO3, where, y = 0.1, 0.3, 0.5, 0.7 and 0.9 are prepared by standard ceramic technique. The X-ray diffraction studies revealed the coexistence of two phases without chemical reaction. The dielectric properties are measured at room temperature in the frequency range from 100 Hz to 5 MHz. Same parameters were also measured by changing the temperature from 25 to 500 °C. The dielectric constant initially decreases rapidly with rise in frequency exhibiting dielectric dispersion at lower frequencies and then remains fairly constant at higher frequencies. The dielectric dispersion observed at low frequencies is of the interfacial polarization type and is attributed to various types of polarizations mechanisms. AC resistivity and dielectric constant show a opposite trend of variation with increase in content of ferrite. The variation of dielectric loss with frequency is in analogous to that of dielectric constant vs. Logf. The dielectric constant vs. temperature curves exhibit peaks around two temperatures i.e. one at around 400 K and other at around 725 K which refers to the ferroelectric and ferromagnetic Curie temperatures. The intensity of the peaks at both the transition temperatures decreases as the fixed applied frequency increases. AC resistivity decreases rapidly with rise in frequency initially, then it do not depend on frequency applied. The rapid fall of resistivity at lower frequency is due to increase in the hopping frequency of the electrons between different ionic sites. The linearity in Logσac vs. Logω2 reveals that the conductivity is due to small polarons. ME output increases with rise in dc magnetic field up to the range 2000–2500 Oe and then decreases for further rise in the field. The peaks observed in the ME output curves is attributed to the enhanced domain wall movements near Curie temperature.

Enhancing the Magnetic Properties of Li-Sb Ferrites

A series of Li0.5 + zSbzLaxFe2.5−2z−xO4 spinel ferrites were prepared by a standard ceramic technique. All samples sintered at 1100 ∘C with a heating rate of 4 ∘C/min. A single-phase cubic spinel structure was confirmed by X-ray diffraction analysis with the appearance of small peaks that represent secondary phases. AC conductivity as a function of frequency and temperature was carried out. The calculated values of the activation energy approve the obtained results and indicate the semiconductor properties of the investigated samples. Due to large ionic radius, La3+ ions cannot completely substitute Fe3+ ions. These ions occupy grain boundaries instead of spinel lattice and form secondary phases after interaction with other ions present in grain boundaries. The magnetic parameters were calculated from the magnetic susceptibility data, in the temperature range 300–900 K at three different magnetic field intensities of 2160, 3000, and 3800 Oe. The data showed a decrease in the magnetic susceptibility till it reaches the Curie temperature (TC). The observed decrease in the Curie temperature with La content was explained on the basis of Neel’s model and the cation distribution. One recommends the use of such sample in the application that demands high resistivity and high Curie temperature.

Structural and magnetic studies of the Co1+xTixFe2(1−x)O4 ferrites

The cubic spinel Co1+xTixFe2(1−x)O4 ferrites, 0.0≤x≤0.5, were prepared by the standard ceramic technique. The samples were examined using the techniques; XRD, FT-IR, SEM and VSM. The average lattice parameter showed dependence on x, whereas the crystallite and grain size and strain did not. The infrared spectra showed six absorption bands in the range of 200–1000cm−1. They were assigned to the corresponding metallic ion–oxygen bonds among the A- and B-sites. The absorption bands ν1 and ν2 and their intensities and force constants F1 and F2 were increased against x. Using the transmitted and absorbed energy, the IR velocity and refractive index and jump rate of vacancies were determined and discussed as functions of x. The trend of sauration magnetization Ms was decreased with x, whereas that of coercivity and anisotropy constant was increased. The determined Debye temperature and stiffness constant of the samples were discussed as functions of x. The absorption bands ν1 and ν2 proved dependence on the distance between magnetic ions (hopping length) LA-A and LB-B at the A- and B-sites, respectively, whereas F1 and F2 proved dependence on Ms.

Structural Rietveld refinement and vibrational study of MgCrxFe2−xO4 spinel ferrites

Spinel ferrites with the general formula MgCrxFe2−xO4 (0≤x≤1) were synthesized by the standard ceramic technique and characterized by X-ray diffraction. The XRD patterns confirmed that the mixed ferrite samples are in the cubic spinel structure which is further validated by Rietveld refinement in the space group Fd3m. The crystal structure and cell parameters were refined by Rietveld analysis. The vibrational study was achieved using Fourier Transform-InfraRed (FT-IR) and Raman spectroscopy. From FT-IR band frequencies, the force constants Kt and Ko , for tetrahedral (A) and octahedral (B) sites respectively, have been calculated and discussed with the trend of bond lengths obtained from Rietveld refinement. For all compositions, Raman spectra revealed the five active modes showing the vibration of O2− ions at both the A-site and B-site ions. The frequencies trend with chromium content of both FT-IR and Raman spectra showed a shift toward higher values for all modes.

Influence of La doping and synthesis method on the properties of CoFe2O4 nanocrystals

Nanocrystals of La doped CoFe2O4 were synthesized using three different techniques: flash autocombustion, citrate–nitrate and the standard ceramic technique. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the obtained nanocrystals. All samples were crystallized in a spinel structure with cubic symmetry. The decrease in the lattice constant was endorsed to the large difference in ionic radii of both La+3 (1.216Å) and Fe (0.65Å) in 6-f coordination. The citrate method displayed superior Ms values amongst all techniques. The coercivity was found to exhibit largest values for the citrate method and then the flash while smallest values are associated with ceramic technique.

Effect of Different Gd3+ Ion Content on the Electric and Magnetic Properties of Lithium Antimony Ferrite

A series of Li0.5+zSbzRxFe2.5−2z−xO4 spinel ferrite with (R = Gd, z = 0.1 and 0.025 ≤ x ≤ 0.200) Sintered at 1100 °C with heating rate of 4 °C/min have been prepared by standard ceramic technique. Structural studies have been performed using X-ray diffraction and Fourier transform infrared spectroscopy. Ac conductivity and dielectric constant as a function frequency and temperature are carried out. The replacement of Gd3+ ions as a rare earth element instead of Fe3+ ions affect directly on the electrical and magnetic properties. By increasing frequency, the conductivity increases because the pumping force of the applied frequency helps in transferring the charge carriers between the different conduction states. Introducing Gd ions into the samples reduce the magnetic moment owing to the decreasing Fe–Fe interaction. The effective magnetic moment also decreases with increasing magnetic field intensity. The general trend of the data is the decrease in TC with increasing the rare earth ionic radius, i.e., the ferromagnetic coupling between the A and B-sites increases with the decrease of the ionic radius of the rare earth ions if it enters the spinel lattice as the result of a small probability.

Magnetic and magnetostrictive properties of Cu substituted Co-ferrites

Copper substituted cobalt ferrite, Co1−xCuxFe2O4 (x=0.00–0.25), nanoparticles were synthesized by sol–gel autocombustion method. X-ray diffraction analysis on the samples was done to confirm the cubic spinel structures and Scherrer equation was used to estimate the mean crystallite size as 40nm. Using the obtained nanoparticles, fabrication of the sintered pellets was done by standard ceramic technique. Magnetic and magnetostrictive measurements on the samples were made by strain gauge and vibrating sample magnetometer techniques, respectively. Maximum magnetostriction and strain derivative values were deduced from the field dependent magnetostriction curves while the magnetic parameters such as saturation magnetization (51.7–61.9emu/g) and coercivity (1045–1629Oe) on the samples were estimated from the obtained magnetic hysteresis loops. Curie temperature values (457–315°C) were measured by a built in laboratory set-up. Copper substituted cobalt ferrites have shown improved strain derivative values as compared to the pure cobalt ferrite and thus making them suitable for stress sensing applications. The results have been explained on the basis of cationic distributions, strength of exchange interactions and net decreased anisotropic contributions due to the increased presence of Co2+ ions in B-sites as a result of Cu substitutions.

Structural Properties, Impedance Spectroscopy and Dielectric Spin Relaxation of Ni-Zn Ferrite Synthesized by Double Sintering Technique

Structural properties, impedance, dielectric and electric modulus spectra have been used to investigate the sintering temperature (Ts) effect on the single phase cubic spinel Ni0.6Zn0.4Fe2O4 (NZFO) ceramics synthesized by standard ceramic technique. Enhancement of dielectric constants is observed with increasing Ts. The collective contribution of n-type and p-type carriers yields a clear peak in notable unusual dielectric behavior is successfully explained by the Rezlescu model. The non-Debye type long range dielectric relaxation phenomena is explained by electric modulus formalism. Fast response of the grain boundaries of the sample sintered at lower Ts sample leading to small dielectric spin relaxation time, t (several nanoseconds) have been determined using electric modulus spectra for the samples sintered at different Ts. Two clear semicircles in impedance Cole-Cole plot have also been successfully explained by employing two parallel RC equivalent circuits in series configuration taking into account no electrode contribution. Such a long relaxation time in NZFO ceramics could suitably be used in nanoscale spintronic devices.

On the Structure and Some Properties of LaCo Co-substituted NiZn Ferrites Prepared Using the Standard Ceramic Technique

AbstractZn0.5Ni0.5-xCoxFe2-yLayO4 ferrites (with x=0, 0.02 and y=0, 0.02) were prepared by an industrial method using the standard ceramic technique and sintered at 1,250°C in air. X-ray diffraction (XRD) was used to obtain the phase formation of the NiZn ferrites. The microstructure of ferrites was investigated by scanning electron microscopy (SEM). The XRD reveals that lattice parameter (a) is decreased and a secondary phase (LaFeO3) is formed in the La–Co co-substituted NiZn ferrite sample, meanwhile, the grain size (D) of this sample decreased obviously by observing SEM photographs. Vibrating sample magnetometry (VSM), B-H analyzer, impedance analyzer and electrometer were carried out in order to characterize some properties of the ferrites. This investigation indicates that, La–Co co-substituted NiZn ferrite sample has higher power loss (Pcv) than other samples at low frequency with an increase in coercive field (Hc) and magnetocrystalline anisotropy (K1), a decrease in initial permeability (μi) and saturation magnetization (Ms). However, at high frequency, the power loss of La–Co co-substituted sample is low, which is attributed to high resistivity (ρ), small grain size (D), less number of Fe2+ ions and low porosity (P).

Magnetic properties of the Ni–Cu–Zn system doped with magnesium oxide

A series of ferrite samples, Ni0.1Cu0.2MgxZn0.7−x Fe2O4, (x=0.00, 0.15, 0.25, 0.35, 0.45, 0.55 and 0.70) has been prepared by the standard ceramic technique, sintered at 1200°C for 2h, and their crystalline structures were investigated by using X-ray diffraction. The IR spectra and the ESR spectra analysis have been studied. DC electrical resistivity, thermoelectric power, charge carriers concentration and charge carrier mobility have been calculated at different temperatures. The value of dc electrical resistivity reach minimum at x=0.35 and above this value the electrical resistivity start to increase. It is noticed that thermoelectric power α for the “Ni–Cu–Zn” system exhibits a positive sign indicating the majority carriers are holes without excluding the presence of electrons. Saturation magnetization Ms for the “Ni–Cu–Zn” system was calculated from M–H loop. It is noted that Ms decreases with Mg content up to x=0.55 and rapidly decrease above x>0.55 for the “Ni–Cu–Zn” system.