Structural and magnetic properties of nanocrystalline Mg–Cd ferrites prepared by oxalate co-precipitation method

Polycrystalline spinel ferrites with general formula Mg_1−x Cd _x Fe₂O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared by oxalate co-precipitation method using high purity sulfates. The samples were sintered at 1,050 °C for 5 h. The structural properties of these samples were investigated by XRD, SEM and FTIR techniques. The X-ray diffraction analysis confirms the formation of single phase cubic spinel structure of all the samples. The lattice constant, X-ray density, physical density, porosity, crystallite size, site radii (r _A, r _B), bond length (A–O, B–O) on tetrahedral (A-site) and octahedral (B-site) were calculated for the samples. The lattice constant increases with increase in Cd²⁺ content. The X-ray density increases with increase in Cd²⁺ content. The crystallite size calculated by Scherrer formula is in the range of 27.79–30.40 nm. Physical densities are calculated by Archimedes principle. The SEM study shows that the grain size increases with increasing Cd²⁺ content. The FTIR spectra shows two strong absorption bands around 576 and 431 cm⁻¹ on the tetrahedral and octahedral sites, respectively. The dependence of saturation magnetization on Cd²⁺ content suggests that A–B and B–B super exchange interaction are comparable in strength. Neel’s two sub lattice model is applicable up to x ≤ 0.4, while Y–K three sub lattice models (canted spin) is predominant for x ≥ 0.4.     

Electrical and dielectric properties of nano crystalline Ni–Co spinel ferrites

Nanocrystalline samples of Ni_xCo₁–_xFe₂O₄, where x = 1, 0.8, 0.6, 0.4, 0.2 and 0, were synthesized by chemical co-precipitation method. The spinel cubic phase formation of Ni–Co ferrite samples was confirmed by X-ray diffraction (XRD) data analysis. All the Bragg lines observed in XRD pattern belong to cubic spinel structure of ferrite. Scanning Electron Microscopy (SEM) technique was used to study the surface morphology of the Ni–Co ferrite samples. Nanocrystalline size of Ni–Co ferrite series was observed in SEM images. Pellets of Ni–Co ferrite were used to study the electrical and dielectric properties. The resistivity measurements were carried out on the samples in the temperature range 300–900 K. Ferrimagnetic to paramagnetic transition temperature (T_c) for all samples was noted from resistivity data. The activation energy below and above T_c was calculated. The dielectric constant (ɛ′) measurements with increasing temperature show two peaks in the temperature range of measurements for all samples under investigation. The peaks observed show frequency and compositional dependences as a function of temperature. Electrical and dielectric properties of nanocrystalline Ni_xCo₁–_xFe₂O₄ samples show unusual behavior in temperature range of 500–750 K. To our knowledge, nobody has discussed such anomalies for nanocrystalline Ni_xCo₁–_xFe₂O₄ at high temperature. Here, we discuss the mechanism responsible for electrical and dielectric behavior of nanocrystalline Ni_xCo₁–_xFe₂O₄ samples.     

Structural, electrical and magnetic properties of copper substituted Zn–Mn ferrites

Optimum composition (x = 0.0–0.75) of copper substituted Zn_0.25Mn_0.75?xCu_xFe₂O₄ ferrites system have been synthesized by simple chemical co-precipitation method. X-ray diffraction pattern of all samples shows characteristic features of nanocrystalline cubic spinel structure of ferrites. The average grain size of the samples was measured using scanning electron micrographs. The saturation magnetization, coercivity and remanance were studied as a function of copper content in the host ferrite materials. Electrical resistivity of the samples was measured by two probe method. The semiconducting nature of the samples was noted from variation of electrical resistivity with temperature. The effect of copper substitution in ferrites was studied through the measurements of structural, electrical and magnetic properties.     

Structural and microwave absorption properties of nanostructured Fe–Co alloys

We analyzed nanostructured Fe₆₀Co₄₀ alloy obtained by mechanical alloying using a planetary ball mill. The prepared powders were characterized using X-ray Diffraction (XRD), Laser particle-measurement, scanning electron microscopy (SEM), X band waveguide and cavity resonator associated with Network analyzer. Obtained results are discussed according to milling time.XRD patterns show after 12 h of milling the formation of a disordered solid solution having body-centerd cubic (bcc) structure. After 36 h milling, morphological studies indicated that the average crystallites size is around 13 nm and the particles average diameter is about 3.6 μm. The microwave absorbing characteristic was enhanced between 0 and 54 h of milling (from ?0.8 to ?13.807 dB) with decreasing in the relative dielectric permittivity ε_r.     

Magnetic properties of Ni–Co–Cr-base Elgiloy

The Ni–Co–Cr-base Elgiloy is one of the commonly used engineering materials. Most applications rely on its high strength, ductility, corrosion resistance and excellent fatigue life over a wide temperature range. However, in the medical application of cerebral aneurysm clips, the alloy is often subjected to strong magnetic fields associated with magnetic resonance imaging (MRI). Its paramagnetic behavior meets MRI safety requirements, but is the source of relatively large artifacts and thus less MRI-compatible for MRI procedure involving the brain. This article reports superconducting quantum interference device (SQUID) measurements on the magnetic properties of a series of Elgiloy wires in either as-drawn or heat-treated conditions. Furthermore, low-temperature calorimetry was employed to reveal the existence of submicroscopic clusters containing ferromagnetic elements such as Ni or Co in the macroscopically paramagnetic matrix. © 1999 Kluwer Academic Publishers     

Structural and magnetic properties of plate-like W-type barium ferrites synthesized with a combination method of molten salt and sol–gel

Plate-like W-type barium ferrites (BaCoZnFe₁₆O₂₇) were prepared by using a combined method of molten salt and a sol–gel process. Pure plate-like W-type barium ferrite with large size about 25 μm and high aspect ratio (diameter/thickness) of ∼35 was obtained at a sintering temperature of 1200 °C. Morphology, phase evolution and static properties of the samples sintered at different temperatures (800–1200 °C) and dynamic magnetic properties of their composites with silicon resin were investigated by using SEM, XRD, VSM and VNA. It was found that the saturation magnetization M_s increased with increasing sintering temperature, whereas the coercivity H_c decreased. Silicon resin composites filled with 45 vol% of the plate-like BaCoZnFe₁₆O₂₇ particles sintered at 1200 °C exhibited promising microwave attenuation properties.     

Interfacial properties of immiscible Co–Cu alloys

Using electromagnetic levitation under microgravity conditions, the interfacial properties of an Cu₇₅Co₂₅ alloy have been investigated in the liquid phase. This alloy exhibits a metastable liquid miscibility gap and can be prepared and levitated in a configuration consisting of a liquid cobalt-rich core surrounded by a liquid copper-rich shell. Exciting drop oscillations and analysing the frequency spectrum, both surface and (liquid–liquid) interfacial tension can be derived from the observed oscillation frequencies. This paper briefly reviews the theoretical background and reports on a recent experiment carried out on board the TEXUS 44 sounding rocket.     

Effect of Al-ion substitution on structural and magnetic properties of Co–Ni ferrites nanoparticles prepared via citrate precursor method

Nanocrystalline Co_0.8Ni_0.2Al_yFe_2−yO₄ (y = 0.00, 0.15, 0.30, 0.45, 0.60, 0.75) powders have been synthesized by the citrate precursor auto-combustion method. The effect of the nonmagnetic aluminum ion substitution on the structural and magnetic properties has been studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy revealed that the obtained powders have a single phase of cubic spinel structure. The crystallite sizes estimated from XRD data have been confirmed using high-resolution transmission electron microscopy (HRTEM). Photographs showed powders consisting of nanosized grains with an average size ranging from 10 to 45 nm, depending on the Al content. Magnetic hysteresis loops were traced at room temperature using vibrating sample magnetometer (VSM). It was found that, due to the aluminum substitution, the values of magnetic losses and saturation and remanent magnetization were decreased, indicating a reduction in the ferrimagnetic behavior. This reduction of magnetization, compared to the undoped sample, was attributed to the increase of spin noncollinearity with increasing Al content. Samples with toroidal forms were used to measure both the initial permeability (μ_i) and Curie temperature (T_C). The obtained results showed a decrease in the values of both μ_i and T_C as the Al content increases. This behavior was explained in view of the weakness in the interaction of A and B sublattices with increasing Al³⁺ ion concentration.     

Structural and physical properties of Ni–Tb–Fe–O system

A series of soft ferrites in the system Ni_1 ? xTb_xFe₂O₄ (0 ≤ x ≤ 0.2), was prepared by a standard ceramic technique. The influence of terbium content was investigated by means of X-ray diffraction, Fourier Transform Infrared (FTIR) spectroscopy and scanning electron microscopy. The X-ray diffraction analysis reveals that the samples have a cubic spinel (single phase) structure for 0 ≤ x ≤ 0.08; for x > 0.08 a small peak of orthorhombic phase (TbFeO₃) appears and becomes more conspicuous with increased terbium substitution. The lattice parameter changes in a non-linear way as a function of terbium content which may be attributed to differences in the ionic radii of the cations involved and the solubility limit of terbium ions. A gradual increase in the bulk density was observed with the increase of terbium concentration, from 5.13 g/cm³ to 5.69 g/cm³. FTIR absorption spectra of the Ni–Tb–Fe–O system were investigated in the wave number range 370–1500 cm^? 1. Each spectrum exhibited two main absorption bands, thereby confirming the spinel structure.     

Structural and Magnetic Properties of Nanocrystalline Mg–Co Ferrites

Mg?CCo nano crystalline ferrites having the general formula Mg_1?x Co _x Fe₂O₄ (x=0, 0.05, 0.1, 0.15, 0.2, 0.25) were prepared by the sol?Cgel method. X-ray powder diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR) were carried out to investigate the structural properties of the samples. X-ray powder diffraction patterns indicated the formation of a spinel structure of the prepared compounds. Fourier Transform Infrared (FTIR) spectroscopy of the samples confirmed the XRD results. The crystallite size, lattice parameters and porosity of samples were calculated by XRD data analysis as a function of cobalt concentration. The dielectric constant (?? _r ), dielectric loss tangent (tan???) and ac electrical conductivity (?? _ac) of nanocrystalline Mg?CCo ferrites were investigated as a function of frequency and Co concentration. The frequency dependence of ?? _r , tan??? and ?? _ac is in accordance with the Maxwell?CWagner model. The effect of Co doping on dielectric and electric properties was explained on the basis of cations distribution in the crystal structure. The saturation magnetization M_S, remanent magnetization M_r and coercivity H_C of all samples were explained as a function of cobalt concentration on the basis of Néel??s two-lattice model.     

Structural and durability properties of hydraulic lime–pozzolan concretes

This paper discusses the results of a suite of tests designed to assess the structural and durability characteristics of hydraulic lime–pozzolan concretes. Specifically, this paper reports on the rate of strength development, elastic modulus, linear shrinkage and rate of carbonation of four hydraulic-lime–pozzolan concretes. The purpose of this investigation was to ascertain the technical feasibility of producing high strength concretes using hydraulic lime and pozzolans as an alternative binder to Portland cement. Results have demonstrated that 28-day compressive cube strengths of 35 MPa can be attained by water-cured lime–pozzolan concretes. The results are presented alongside comparable test results for Portland-cement (CEMI) and blastfurnace cement (CIII/A) concretes. Similarities and differences in material characteristics are discussed in terms of fundamental material properties and in terms of the emergent threats and opportunities for the potential development of these novel concretes.     

Magnetic and dielectric properties of Co–Zn ferrite

Nanocrystalline powders of Co substituted Zn ferrite with the chemical formula Co_xZn_1−xFe₂O₄ (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were synthesized by sol–gel autocombustion method using tartaric acid as fuel agent. The samples were sintered in static air atmosphere for 7 h at 773 K, 7 h at 973 K and 10 h at 1173 K. The organic phase extinction and the spinel phase formation were monitored by means of Fourier transform infrared spectroscopy. The X-ray diffraction patterns analysis confirmed the spinel single phase accomplishment. Crystallite size, average grains size, lattice parameter and cation distribution were estimated. Magnetic behavior of the as-obtained samples by means of M-H hysteresis measurements was studied at room temperature. Permeability and dielectric permittivity at room temperature versus frequency was the subject of a comparative study for the Co_xZn_1−xFe₂O₄ series. In agreement with the proposed cation distribution the sample with Co_0.8Zn_0.2Fe₂O₄ formula exhibits the optimal magnetic and dielectric properties.     

Preparation and properties of WC–Co textured components

Abstract

WC–Co components having one {0001} textured surface have been produced and tested. The textured surface has beenfound to be harder and more resistant to fracture and abrasive wear than standard surfaces. A method is proposed to produce WC–Co components having a bulk {0001} texture.

MST/1337     

Structural,electrical, and magnetic properties of erbium (Er3+) substituted Cu–Cd nano-ferrites

In the present work, we reported the structural, electrical, and magnetic properties of erbium Er³⁺-substituted Cu–Cd nano-ferrites with generalized formula Cu_0.8Cd_0.2Er_xFe_2?xO₄ (where x?=?0.000, 0.0010, 0.0015, 0.002, 0.0025, 0.003), as synthesized by the Citrate-Gel Auto-Combustion. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies were carried out to investigate their microstructural and surface morphology. The XRD measurements confirm pure cubic spinel phase composition of these nanoparticles. The crystallite size ranges over 9.22–19.22 nm and it reduces with the increase in erbium Er³⁺ concentration from 0.000 to 0.003. The vibration properties were carried out by using FTIR spectrometer. The two probe measurements were used to determine DC resistivity, Curie temperature, and DC conductivity. The plot between DC electrical resistivity and temperature indicates the semiconductor behavior. At room temperature, the vibrating sample magnetometer (VSM) was used to investigate magnetic properties, and the observed values revealed the ferrimagnetic behavior with high saturation magnetization (34.24 emu/g) and high coercivity (1121.70 Oe).

     

Structural and dielectric properties of nanocrystalline Nd<Superscript>3+</Superscript> substituted nickel–zinc ferrites

Ferrite samples with general formula Ni_1−xZn_xNd_yFe_2−yO₄ (x = 0, 0.2, 0.4, 0.6, 0.8 and 1; y = 0.01, 0.02 and 0.03) were synthesized by oxalate co-precipitation technique. The X-ray diffraction study confirms the formation of single-phase cubic spinel structure. The lattice constant of the samples increases with increase in zinc content and obeys Vegard’s law. On Nd³⁺ substitution lattice constant of the samples slightly increases except zinc ferrite. The frequency dependence of the dielectric constant, dielectric loss and AC conductivity of the samples were determined in the frequency range from 20 Hz to 1 MHz at room temperature. The experimental results reveal that the dielectric constant and dielectric loss decreases where as AC electrical conductivity increases with increase in frequency. The dielectric loss increases with increase in zinc content whereas it decreases with increase in Nd³⁺ content. There is no appreciable change in permittivity of the samples with increase in Nd³⁺ content. Permeability of all the samples increases with increase in Nd³⁺ content. Because of lower dielectric loss, Nd³⁺ substituted Ni–Zn ferrites are useful in electronic devices.     

Structural characterizations and optical properties of new Li–Sr–Nb-phosphate glasses

A new Li₂O–SrO–Nb₂O₅–P₂O₅ glass system was prepared by a high-temperature alumina crucible, and structural characterization and optical properties were investigated. Proper content of Li₂O and Nb₂O₅ was employed to replace partial SrO and P₂O₅ to improve the optical properties. It was observed that the enhancement of the refractive index from 1.75 to 1.85 is mainly due to the Nb₂O₅ content. An addition of Li₂O significantly increases the optical transmittance; optical transparency can be enhanced from 60% to higher than 85% in the UV–visible region with addition of 20–40 mol% Li₂O species. However, optical transmittance is monotonically decreased from about 90% to 80% under 10–30 mol% Nb₂O₅ addition. The 40P₂O₅–20Nb₂O₅–20SrO–20Li₂O glasses demonstrate the optimum refractive index (n > 1.75) and high optical transparency (>80%) in the UV–visible region.     

Effect of γ-rays irradiation on the structure and magnetic properties of Mg–Cu–Zn ferrites

The effect of γ-irradiation on the structure and magnetic properties of ferrite samples with chemical formula Mg _x Cu_0.5−x Zn_0.5Fe₂O₄ (where x = 0.0, 0.2, and 0.4) prepared by conventional ceramic method has been studied. X-ray diffraction patterns (XRDPs) indicated the presence of a single spinel phase for all the investigated samples. The initial permeability and magnetization were measured, before and after irradiation on toroidal samples used as transformer cores. The initial permeability μ_i was measured as a function of temperature at constant frequency of 10 kHz and Curie temperatures (T _C) were determined. It was found that, due to irradiation, both of lattice parameter and porosity were increased. On the other hand, the values of magnetization and initial permeability were decreased as a result of irradiation. In addition, there was a decrease in the crystallite size, homogeneity, and the values of Curie temperature with significant decrease in the values of μ_i and T _C for the sample with x = 0.0. The results are discussed in the light of γ-rays interaction with ferrite lattice.     

Electrical and magnetic properties of Mn–Ni–Zn ferrites processed by citrate precursor method

Mn_xNi_0.5−xZn_0.5Fe₂O₄, (x=0.05, 0.1, 0.2, 0.3, 0.4) ferrites synthesized by the citrate precursor method are investigated in the present work. Compositional variation of AC resistivity is studied and values up to 10³ times greater than those for samples prepared by the conventional ceramic method are observed. It is found that resistivity decreases with increase in Mn concentration except for x=0.3, where it shows a rise. Frequency variations of both dielectric constant and relative loss factor (rlf) are reported in the present work. It is observed that dispersion in dielectric constant is greatly influenced by the Mn concentration. Possible mechanisms contributing to these properties are discussed. Hysteresis properties are also reported.