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.     

Structural and magnetic properties of Li–Al-substituted Ni–Zn–Cu ferrite powders prepared via chemical coprecipitation method

Li–Al substituted Ni–Zn–Cu ferrite powder specimens with the nominal composition Ni_0.25?2x Li _x Al _x Cu_0.15Zn_0.60Fe₂O₄ (x?=?0.00, 0.01, 0.02, 0.03, 0.04) were prepared via an improved chemical coprecipitation method. An X-ray diffractometer, a scanning electron microscope and a vibrating sample magnetometer were used to study their structural and magnetic properties. It is found that all the specimens exhibit typical single-phase spinel structures after annealing, and the saturation magnetization decreases with increase of x. The initial susceptibility first increases but then decreases, and obtains the maximum when x?=?0.02, which shows the proper content of Li–Al substitutions is favourable for the increase of initial susceptibility. It is also found that the Li–Al substitutions affect the grain growth slightly.     

Microwave absorbing properties of double-layer cementitious composites containing Mn–Zn ferrite

Double-layer cementitious composites filled with Mn–Zn ferrite as microwave absorbers were designed based on the impedance matching theory and electromagnetic wave propagation laws. The results showed that the addition of silica fume can improve the impedance matching between the cementitious composites and free space. Comparing with the single-layer structure, the reflectivity of the double-layer cementitious plates can decrease by 6–8 dB and decrease by 15 dB maximum with 30 wt.% ferrite; in addition, the reflectivity of electromagnetic wave is lower than 10 dB in the frequency range of 11.4–18 GHz. These composites can be potentially used as electromagnetic interference (EMI) materials for buildings.     

The effect of chelating/combustion agent on catalytic activity and magnetic properties of Dy doped Ni–Zn ferrite

The spinel ferrite Ni_0.8Zn_0.2Fe_1.98Dy_0.02O₄ was prepared by sol–gel low temperature autocombustion method using four different chelating/combustion agents: citric acid, tartaric acid, urea and cellulose. Infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) specific surface area measurement, the catalytic H₂O₂ decomposition and the magnetic behavior were employed to investigate the influence of the combustion agents on structural characteristics, catalytic activity and magnetic properties. Spinel-type phase in the nano-scale domain was accomplished during sol–gel synthesis and was confirmed by XRD and IR. The best catalytic activity is belonging to the sample obtained using urea, which shows the smallest grain size (SEM), the highest specific surface area (BET measurements) and DyFeO₃ phase (XRD), while ferrimagnetic behavior prevails for all the samples independently of fuel agent.     

Aspect ratios and morphology of acicular ferrite in C–Mn–Ni weld metals

Abstract

The aspect ratio and morphology of acicular ferrite formed in C–Mn–Ni weld metals and the effect of nickel and oxygen contents have been investigated. The experimental results revealed that nickel has a strong effect on the acicularity of acicular ferrite in C–Mn–Ni weld metals. High nickel contents resulted in sharper acicular ferrite laths with a larger aspect ratio. It is considered that the two dominant mechanisms are the role of nickel in changing the balance of incoherent/coherent growth ledges, and the transformation temperatures at which this growth takes place. Reducing the oxygen content in the weld metals was also found to increase the aspect ratio.

MST/3071     

Precipitation in Cu–Ni–Si–Zn alloy for lead frame

The aging of Cu–Ni–Si–Zn alloy for lead frame is investigated. The results showed that the peak of hardening effect occurs after aging for about 1 h and the electrical conductivity increases continuously with aging times. The hardness of the alloy reached a peak at 430–460 °C for 2 h and electrical conductivity reached a peak at 500–550 °C and continuously decreased afterwards. The cold rolling prior to the aging treatment was used to increase the precipitation rate. The precipitates responsible for the age-hardening effect are disc-shaped δ-Ni₂Si, which has an orthorhombic structure.     

Microstructure and magnetic studies of Mg–Ni–Zn–Cu ferrites

Soft Mg–Ni–Zn–Cu spinel ferrites having general chemical formula Ni_xMg_0.5−xCu_0.1Zn_0.4Fe₂O₄ (where x = 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by standard double sintering ceramic method. The samples were characterized by X-ray diffraction at room temperature. The X-ray diffraction (XRD) study revealed that lattice parameter decreases with increase in Ni content, resulting in a reduction in lattice strain. The electrical and magnetic properties of the synthesized ferrites have been investigated as a function of temperature. The variation of initial permeability and AC susceptibility with temperature exhibits normal ferrimagnetic behavior. The variation of initial permeability with frequency is studied. The Curie temperature (T_C) in the present work was determined from initial permeability and AC susceptibility. The Curie temperature increases with Ni content.     

Anomalies in electrical and dielectric properties of nanocrystalline Ni–Co spinel ferrite

Nanocrystalline Ni-substituted cobalt ferrite sample is prepared by chemical co-precipitation method. X-ray diffraction and scanning electron microscopy techniques are used to obtain structural and morphological characterizations. Nanocrystalline nature is clearly seen in SEM picture. Variation of electrical resistivity as a function of temperature in the range 300–900 K is investigated. ln ρ versus 1/T plot shows four break resulting into five regions in 300–900 K temperature range of measurements. The magnetic transition temperature of the sample is determined from resistivity behavior with temperature. The activation energy in different regions is calculated and discussed. Variation of dielectric constant (?′) with increasing temperature show more than one peak; one at around 773 K and other around 833 K, which is unusual behavior of ferrites. The observed peaks in ?′ variation with temperature show frequency dependence. Electrical and dielectric properties of Ni_0.4Co_0.6Fe₂O₄ sample show unusual behavior in the temperature range 723–833 K. To our knowledge, nobody has discussed anomalous behavior in the temperature range 723–833 K for Ni_0.4Co_0.6Fe₂O₄. The possible mechanism responsible for the unusual electrical and dielectric behavior of the sample is discussed.     

Preparation and properties of electroless Ni–Zn–P alloy films

Electroless deposition of Ni–Zn–P layers was studied on steel electrodes by varying the bath temperature (40–90°C), pH and chemical composition. The deposition parameters were optimized. Alloys containing 70–86 wt % Ni, 6–20 wt % Zn and 6–10 wt % P are obtained at 20 m h^–1 and 85°C. Corrosion measurements were performed in aerated 5% sodium chloride solution, the corrosion potential and current density are, respectively, –0.49 V/SCE and 2.6 A cm^–2.     

Influence of evolving microstructure on magnetic-hysteresis characteristics in polycrystalline nickel–zinc ferrite,Ni0.3Zn0.7Fe2O4

We report some research findings on the parallel evolutions of microstructural properties and magnetic hysteresis-loop properties; we attempt to elucidate their relationships. The Ni_0.3Zn_0.7Fe₂O₄ toroidal samples were prepared via high-energy ball milling and subsequent moulding; the samples with nanometer/submicron sized compacted powder were sintered from 600 °C to 1400 °C using 100 °C increments. An integrated analysis of phase, microstructural and hysteresis data would point to the existence of three distinct shape-differentiated groups of B–H hysteresis loops which belong to samples with weak, moderate and strong magnetism. The observed grain size with respect to the magnetic-hysteresis behaviour varied from 0.19 μm to 0.23 μm, 0.24 μm to 0.43 μm and 1.07 μm to 4.98 μm for weak, moderate and strong ferromagnetic behaviour respectively. The first occurrence of a strikingly erect and well-defined sigmoid-shape was observable only when sufficient single-phase purity and crystallinity and a sufficiently high volume fraction of multi-domain grains (>0.25 μm) were attained.     

Temperature dependence on the mass susceptibility and mass magnetization of superparamagnetic Mn–Zn–ferrite nanoparticles as contrast agents for magnetic imaging of oil and gas reservoirs

The mass susceptibility (χ_mass) and mass magnetization (M_mass) were determined for a series of ternary manganese and zinc ferrite nanoparticles (Mn–Zn ferrite NPs, Mn_xZn_1?xFe₂O₄) with different Mn:Zn ratios (0.08 ≤ x ≤ 4.67), prepared by the thermal decomposition reaction of the appropriate metal acetylacetonate complexes, and for the binary homologs (M_xFe_3?xO₄, where M = Mn or Zn). Alteration of the Mn:Zn ratio in Mn–Zn ferrite NPs does not significantly affect the particle size. At room temperature and low applied field strength the mass susceptibility increases sharply as the Mn:Zn ratio increases, but above a ratio of 0.4 further increase in the amount of manganese results in the mass susceptibility decreasing slightly, reaching a plateau above Mn:Zn ≈ 2. The compositional dependence of the mass magnetization shows less of a variation at room temperature and high applied fields. The temperature dependence of the mass magnetization of Mn–Zn ferrite NPs is significantly less for Mn-rich compositions making them more suitable for downhole imaging at higher temperatures (>100 °C). For non-shale reservoirs, replacement of nMag by Mn-rich Mn–Zn ferrites will allow for significant signal-to-noise enhancement of 6.5× over NP magnetite.     

Depth dependent hardness variation in Ni–P amorphous film under nanoindentation

Abstract

The deformation behaviour and the depth dependent hardness variation in Ni–P amorphous alloy were investigated by nanoindentation. It was found that in addition to circular shear bands around the indent and on the indent surface, which have been previously observed, straight shear bands on the indent surface were also formed during nanoindentation. The indentation depth dependent hardness in the metallic glass is not modelled by the conventional dislocation based strain gradient theory for crystalline materials; instead it can be well described by a function of the inverse square root of the indentation depth. The structure evolution beneath the indentor is proposed to be the probable cause for the length scale dependent properties in metallic glass.     

Deeply Reconstructed Hierarchical Ni–Co Microwire for Flexible Ni–Zn Microbattery with Excellent Comprehensive Performance

The rise of flexible electronics calls for efficient microbatteries (MBs) with requirements in energy/power density, stability, and flexibility simultaneously. However, the ever-reported flexible MBs only display progress around certain aspects of energy loading, reaction rate, and electrochemical stability, and it remains challenging to develop a micro-power source with excellent comprehensive performance. Herein, a reconstructed hierarchical Ni–Co alloy microwire is designed to construct flexible Ni–Zn MB. Notably, the interwoven microwires network is directly formed during the synthesis process, and can be utilized as a potential microelectrode which well avoids the toxic additives and the tedious traditional powder process, thus greatly simplifying the manufacture of MB. Meanwhile, the hierarchical alloy microwire is composed of spiny nanostructures and highly active alloy sites, which contributes to deep reconstruction (≈100 nm). Benefiting from the dense self-assembled structure, the fabricated Ni–Zn MB obtained high volumetric/areal energy density (419.7 mWh cm⁻³, 1.3 mWh cm⁻²), and ultrahigh rate performance extending the power density to 109.4 W cm⁻³ (328.3 mW cm⁻²). More surprisingly, the MB assembled by this inherently flexible microwire network is extremely resistant to bending/twisting. Therefore, this novel concept of excellent comprehensive micro-power source will greatly hold great implications for next-generation flexible electronics.     

Microstructure and electrical properties of Ni–Zn manganite ceramics

Nickel zinc manganite ceramics Mn_2.34−xNi_0.66Zn_xO₄ (0≤x≤1.02) were investigated using structure, microstructure and electrical property interrelationships. The resistivity increased with zinc content whereas the activation energy remained constant. The drift of resistivity under thermal constraint, commonly observed in NTC thermistors was almost nil when the zinc content was sufficiently high (x≥0.7). Homogeneous microstructures and high densities were obtained when the ceramics were prepared from fine powders. The Ni/Zn/Mn/O system prepared by ‘chimie douce’ has interesting NTC properties for industrial applications.     

The effects of silica content,sintering temperature and sintering time on a Ni‐Zn ferrite

Abstract

In this experiment the effects of silica content, sintering time, and sintering temperature on the microstructure and magnetic properties of a ferrite, Ni₀₃₂Zn₀₆₈Fe₂O₄, were studied.

The initial permeability is reduced only slightly when the silica content is less than 0.2 wt %. The Q value is proportional to the silica content approximately. The peak value of μ _iQ product is about constant when the silica content is less than 0.2 wt %.

The best sintering temperature is between 1175°C and 1200°C. The addition of silica (<0.2 wt%) enhances the rate of densification, but the control of sintering time has to be more precise because the addition of silica makes the shape of μ _iQ product peak become sharper and narrower.     

In–Ga–Zn–O thin film transistor with HfO2 gate insulator prepared using various O2/(Ar + O2) gas ratios

We have investigated the effect of the deposition of an HfO₂ thin film as a gate insulator with different O₂/(Ar + O₂) gas ratios using RF magnetron sputtering. The HfO₂ thin film affected the device performance of amorphous indium–gallium–zinc oxide transistors. The performance of the fabricated transistors improved monotonously with increasing O₂/(Ar + O₂) gas ratio: at a ratio of 0.35, the field effect mobility of the amorphous InGaZnO thin film transistors was improved to 7.54 cm²/(V s). Compared to those prepared with an O₂/(Ar + O₂) gas ratio of 0.05, the field effect mobility of the amorphous InGaZnO thin film transistors was increased to 1.64 cm²/(V s) at a ratio of 0.35. This enhancement in the field effect mobility was attributed to the reduction of the root mean square roughness of the gate insulator layer, which might result from the trap states and surface scattering of the gate insulator layer at the lower O₂/(Ar + O₂) gas ratio.