Effects of Ni2+ concentration on the composition,structure, magnetic properties,and DC-bias superposition characteristics of NiCuZn ferrites

Ni_xCu_0.2Zn_yFe_1.98O₄ (x = 0.16, 0.26, 0.35, 0.43, 0.50; y = 0.8?x) ferrites were prepared via solid-state reaction. The influence of Ni²⁺ concentration on ferrites composition, microstructure, magnetic properties and DC-bias superposition characteristics was studied by XRD, SEM, XPS, and VSM. Then, the effect of magnetic properties on the DC-bias superposition characteristics was analyzed. The results showed that the ferrites sintered at 900 °C for 3 h were all in pure spinel phase with an average grain size of 7.5 μm and a relative density of about 5.15 g cm^?3. With the increase in Ni²⁺ concentration, the saturation magnetization (M_s) and coercivity (H_c) of ferrites increased, but the magnetocrystalline anisotropy constant (K₁) first increased and then decreased. And the M_s, H_c, and K₁ of the specimen with x = 0.43 were 63.62 emu·g^?1, 27.36 Oe, and 1813.17 Oe·emu·g^?1, respectively. In particular, the specimen of x = 0.50 achieved the best DC superposition characteristics, where the H_70% was about 220 A m^?1. The incremental permeability of the specimens decreased rapidly at a bias magnetic field <400 A m^?1. The variation mainly originated from the domain wall displacement, and the rate of decrease was influenced by both M_s and K₁. At a bias magnetic field ≥400 A m^?1, the incremental permeability of the specimens decreased slowly, mainly because the number of domain walls decreased until disappearing, and the specimens tended to become a single domain structure. And the rate of decrease of incremental permeability was mainly affected by K₁.     

Effects of Bi2O3 and Li2OB2O3Bi2O3SiO2 glass on electromagnetic properties of NiCuZn/BaTiO3 composite material at low sintering temperature

Bi₂O₃ and Li₂OB₂O₃Bi₂O₃SiO₂ (LBBS) glass were introduced into Ni_0.15Cu_0.24Zn_0.61Fe₂O₄BaTiO₃ ((NCZF-BTO) composite materials as sintering aids and sintered at 920?°C. Effects of Bi₂O₃ and LBBS glass on phases, microstructures, magnetic and dielectric properties of these composites were comparatively studied. In contrast to undoped composites, the addition of Bi₂O₃ or LBBS glass to samples enhances performance. Hence, when Bi₂O₃ content reached 1.5?wt%, saturation magnetization (4πM_s) increased from 3825.4 to 4912.5 Gs, static permeability (μ₀) increased from 53.2 to 197, and dielectric constant (ε′) increased from 18.3 to 23.4. When LBBS glass content reached 1.5?wt%, 4πM_s increased to 4145.6 Gs, μ₀ increased to 79.3, ε′ increased to 25.4. However, both coercivity (H_c) and dielectric loss (tan?δ) were reduced. In short, Bi₂O₃ promoted magnetic properties, whereas LBBS glass promotes dielectric properties more effectively.     

Effects of Bi2O3-Nb2O5 additives on microstructure and magnetic properties of low-temperature-fired NiCuZn ferrite ceramics

NiCuZn ferrite with superior magnetic performance is vital ceramic material in multilayer chip inductors (MLCI) applications. In this study, low-temperature-sintered Ni_0.22Cu_0.2Zn_0.58Fe₂O₄ ferrite ceramic doped with 1.0?wt% Bi₂O₃-x?wt% Nb₂O₅ (where x?=?0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) was synthesized via solid-state reaction method. Effects of Bi₂O₃-Nb₂O₅ additives on microstructures and magnetic properties of NiCuZn ferrite ceramics sintered at 900?°C were systematically investigated. Results indicate that an appropriate amount of Bi₂O₃-Nb₂O₅ composite additives can significantly promote grain growth and densification of NiCuZn ferrite ceramics when sintered at low temperatures. Specifically, samples doped with 1.0?wt% Bi₂O₃ and 0.4?wt% Nb₂O₅ additives exhibited excellent initial permeability (~ 410 @ 1?MHz), high cutoff frequency (~ 10?MHz), high saturation magnetization (~ 54.92?emu/g), and low coercive force (~ 20.32?Oe). These observations indicate that NiCuZn ferrite ceramics doped with appropriate amounts of Bi₂O₃-Nb₂O₅ additives are great candidate materials for MLCI applications.     

Sintering and cooling atmosphere effects on the microstructure,magnetic properties and DC superposition behavior of NiCuZn ferrites

This study investigated the sintering and cooling atmosphere effects on the microstructure and magnetic properties of NiCuZn ferrites. The copper-rich phase segregated during sintering near the grain boundaries. The sample sintered in N₂ and cooled in air (N₂-Air) exhibited the highest amount of segregated copper-rich second phase, followed by the sample sintered and cooled both in air (Air-Air). However, no precipitate was observed for the sample sintered and cooled both in N₂ (N₂-N₂). This can be explained by the fact that Cu²⁺ was reduced into Cu⁺, promoting Cu₂O phase precipitation and then reacting with CuO to form a liquid phase. The Air-Air sample exhibited the highest initial permeability (μ_i ≈ 250) and saturation magnetization (B_s ≈ 88 emu/g), followed by N₂-N₂ (μ_i ≈ 180, B_s ≈ 82) and N₂-Air (μ_i ≈ 150, B_s ≈ 80). The highest DC superposition behavior was obtained for N₂-Air sample due to the highest nonmagnetic copper-rich precipitate thickness at the grain boundaries.     

Nb5+ ion substitution assisted the magnetic and gyromagnetic properties of NiCuZn ferrite for high frequency LTCC devices

Nowadays, developing nickle zinc ferrites with excellent magnetic and gyromagnetic properties are of great importance for solving the matching problem of 5G communication system. However, much is discussed about soft magnetic properties, but little is reported gyromagnetic properties that is critical for microwave device applications. Herein, Nb⁵⁺ ions substituted Ni_0.29Cu_0.18Zn_0.53Nb_xFe_2-xO₄ (x = 0.00-0.05), possessing high saturation magnetization, approriate initial permeability, high cut-off frequency and low ferromagnetic resonance linewidth (@9.55 GHz), were synthesized by low-temperature firing (900 °C). The phase structure and morphology evolutions were studied in detail. The results of morphology observations revealed that Nb⁵⁺ substitution has significant role in determining produce compact and uniform microstructures of NiCuZn ferrites via suppress the grain growth, which further corresponding enhance the magnetic and gyromagnetic properties. As a result, a uniform and compact grain size can be obtained, corresponding to the change of magnetic and gyromagenetic properties have different trends. Enhanced magnetic and gyromagnetic performance including high initial permeability (μ' = 203 @1 MHz), saturation magnetization (4πM_s = 3966 Gauss) and low ferromagnetic resonance linewidth (ΔH = 203 Oe) of the NiCuZn ferrites is achieved though adjusting Nb⁵⁺ ions substitution. More importantly, this work not only for low temperature co-fired ceramic (LTCC) technology but also for high frequency and microwave frequency devices including phase shifter and radars.     

Microstructure,magnetic, and power loss characteristics of low-sintered NiCuZn ferrites with La2O3-Bi2O3 additives

Low-temperature-sintered Ni_0.5Cu_0.125Zn_0.375Fe_1.98O₄ ferrites co-added with x wt% (x = 0.00-0.25 wt%) La₂O₃ and 0.25 wt% Bi₂O₃ were successfully prepared via conventional solid-phase reaction method. The phase composition, microstructure, magnetic properties, and especially power loss variation of the samples were systematically studied. The results showed that all samples possessed a single spinel phase structure at a sintering temperature of 900°C, exhibiting high degree of densification and uniform grains. The appropriate amount of La₂O₃ additive improved the saturation flux density and permeability of NiCuZn ferrites, simultaneously reducing the coercivity and power loss. The maximum permeability and the lowest power loss were achieved at x = 0.15 wt%. The corresponding sample had the homogeneous microstructure and excellent magnetic properties, being a promising low-temperature co-fired ferrite candidate for magnetic power components.     

Electrosynthesis of Co,Ni and Zn ferrites nanoparticles in the presence of external magnetic field

Magnetic complex oxides of iron nanoparticles are among the most important materials that have been studied. They have been widely used in different areas such as electronic devices, information storage, biomedical areas, drug-delivery, catalyst, and wastewater treatment. In different applications of nanoparticles, the shape and size of particles are very important because the electrical, optical, and magnetic properties of the nanoparticles depend on their dimension. In this study, nanoparticles of cobalt, nickel, and zinc ferrites were synthesized in uniform size by an electrochemical technique. First, the anode was made electrochemically by depositing each metal of zinc, nickel, and cobalt on the iron sheet from the solutions of 0.1 M Co²⁺, Ni²⁺, and Zn²⁺ ions as the precursor. Then the electrosynthesis of ferrite nanoparticles was performed in a second electrochemical cell where the prepared electrode was anode and stainless steel (316L) was cathode in the electrolyte solution of CTAB 0.04 M. The optimized value of current density was applied to the electrochemical cell. After then the same synthesis was carried out in the magnetic field supplied by two magnets. The prepared nanoparticles were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The magnetic properties were investigated by vibrating sample magnetometer (VSM). The comparison of two samples prepared in the magnetic field and without it showed the average size of the samples synthesized in the magnetic field was in the narrower size distribution of 20–30 nm and the saturation magnetization of the nanoparticles increased in the magnetic field.     

Effects of solid-state reaction temperature on the activation energy and DC-bias superposition of NiCuZn ferrites based on master sintering curve

This work reports our recent studies on the microstructure and properties of NiCuZn ferrites, with particular interests in effects of solid-state reaction temperature on the sintering activation energy and DC-bias superposition characteristic. The theory of master sintering curve was used to investigate the densification evolutions of NiCuZn ferrites during sintering process. Experimental results demonstrated that materials with solid-state reaction temperature of 850°C exhibited the lowest value of activation energy, 577.6?kJ?mol^?1. When the solid-state reaction temperature was lower than 800°C, reaction could not be perfectly completed, which would hinder the consolidation process during heating up. In addition, increased solid-state reaction temperature could facilitate the homogeneous grain growth, reduce the final grain size and improve DC-bias superposition characteristic. Possible mechanisms behind are discussed.     

On the structural and magnetic properties of La-substituted NiCuZn ferrites prepared using egg-white

Ni_0.50Cu_0.25Zn_0.25La_xFe_2−xO₄ ferrites (with x = 0.00–0.09) were prepared by a simple method using metal nitrates and freshly extracted egg white. The proper calcination temperature for ferrites formation was estimated using thermo-gravimetry technique (TG). The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared spectroscopy (FT-IR) measurements. XRD of the powders calcined at 550 °C for 2 h showed single-phase crystalline cubic ferrites with crystallite sizes in the range 17.2–21.6 nm. Both the lattice parameter and X-ray density are found to increase by the addition of rare earth ion. TEM image showed agglomerated nano-particles with irregular sizes and shapes. FT-IR spectra showed two absorption bands (ν₁ and ν₂) attributed to stretching vibration of tetrahedral and octahedral complex Fe³⁺–O²⁻, respectively. The shifting of the ν₂ band towards lower frequencies indicates the preference of lanthanum ions to occupy the octahedral sites. The effect of La-substitution on the magnetic properties was studied using vibrating sample magnetometry (VSM) and susceptibility measurements. The decrease in the saturation magnetization with increasing La content can be attributed to the decreasing of Fe³⁺–Fe³⁺ interactions in the octahedral sites. Coercivity shows size dependent behavior due to the combination of surface effect and surface anisotropy. The obvious decrease in the Curie temperature (T_C) with increasing La content indicates that the highly paramagnetic character of La³⁺ ions decreases the ferromagnetic region at the expense of the paramagnetic one.     

Effects of Sr doping on the structure,magnetic properties and microwave absorption properties of LaFeO3 nanoparticles

Lightweight, broadband microwave absorbing materials, with strong absorption capacities, are an urgent demand for practical applications. The microstructural and microwave absorption properties of LaFeO₃ samples prepared by a sol-gel method using different amounts of Sr are investigated systematically. X-ray diffraction and Rietveld refinement studies showed that Sr²⁺ doping can distort the crystal structure of LaFeO₃, leading to lattice expansion and spin tilt of the Fe-O-Fe bond angle. The improvement of magnetic properties mainly originates from the synergistic effect of the bond angle spin tilt and crystal structure defects. Oxygen vacancies will be generated due to the fluctuations in the valence state of Fe³⁺ resulting from the substitution of La³⁺ by Sr²⁺ as deduced from the X-ray photoelectron spectroscopy analysis. The generation of oxygen vacancies, electronic hopping and polarization loss may be one of the main reasons for changes in the electromagnetic parameters. The minimum reflection loss (RL) of La_1–xSr_xFeO₃ nanoparticles with the Sr doping of 0.2 can reach approximately -39.3 dB at 10 GHz for the thickness of 2.2 mm, and the effective absorption bandwidth (RL ≤ -10 dB) can reach approximately 2.56 GHz. In addition, the La_1–xSr_xFeO₃ nanoparticles also can obtain better microwave absorbing performance in the C-band (4–8 GHz) with the minimum RL of -36.8 dB for the matching thickness of 3.0 mm and Sr content of 0.3. Consequently, La_1–xSr_xFeO₃ nanoparticles are promising materials for use in a high-performance and adjustable electromagnetic wave absorber, particularly in C-band and X-band.     

Effects of dopants on the reliability of low temperature sintered Li2ZnTi3O8 ceramics

The effects of acceptor dopant (typical Mn²⁺) and donor dopant (typical V⁵⁺) on the reliability of Li₂ZnTi₃O₈ based low temperature co-fired ceramics (LTCC, in short) have been investigated. Large difference occurs among different types of dopants. V⁵⁺ doping decreases the breakdown voltage of the multilayer capacitors which were manufactured by low temperature sintered Li₂ZnTi₃O₈ ceramics, however, Mn²⁺ doping increases the breakdown voltage and lowers down the leakage current significantly. This may very likely due to the fact that donor induces the generation of weak bound electrons while acceptor capture the weak bound electrons. The results suggest that Mn²⁺ is a very effective additive for improving the reliability of low temperature sintered Li₂ZnTi₃O₈ ceramics.     

Influence of Zn2+ doping on the microstructure and magnetic properties of CuFeO2

The mineral delafossite CuFeO₂ exhibits triangular spin frustration with strong magnetoelectric coupling and unique magnetic properties. In this work, the crystal structure, microstructure, oxidation states, and magnetic properties of synthetic CuFe_1-xZn_xO₂ samples have been systematically studied with a view to understanding the effect of small amounts of the diamagnetic Zn²⁺ ion on the magnetoelectric properties of CuFeO₂. Samples were confirmed by XRD as having a single-phase delafossite structure, although the introduction of Zn²⁺ resulted in distortion of the crystal lattice. Addition of Zn²⁺ also increased the particle size and the number of pores, but did not change the oxidation states of either the Cu or Fe. Magnetic susceptibility measurements show that Zn²⁺ disrupted the antiferromagnetic structure of the samples, and resulted in generation of significant ferromagnetism. Overall, the magnetic properties of CuFeO₂ are closely related to ionic substitution, lattice distortion and microscopic defects.     

Effects of pH value on the microstructure and magnetic properties of solution combusted Fe3O4 powders

Magnetite (Fe₃O₄) powders were prepared by solution combustion synthesis method using conventional and microwave ignition at various pH values of starting solution, adjusted by NH₄OH. The chelated species in dried gels were predicted by theoretical calculations and Fourier transform infrared spectroscopy. The combustion reaction rate strongly depended on pH values as investigated by thermal analysis. Phase evolution and structure characterized by X-ray diffraction method showed single phase and well-crystalline Fe₃O₄ powders which were achieved using conventional ignition at pH ≥ 7. However, the microwave ignition led to the formation of impure FeO phase together with Fe₃O₄. The microwave combusted powders exhibited the disintegrated structure in comparison with the bulky microstructure for conventionally combusted powders, as observed by scanning electron microscopy. Magnetic properties of the as-combusted powders studied by vibration sample magnetometry showed the highest saturation magnetization of 81.3 emu/g for conventional ignition at pH of 7, due to the high purity and large crystallite size.     

Enhanced electromagnetic properties of low-temperature sintered NiCuZn ferrites by doping with Bi2O3

NiCuZn ferrite is a material suitable for low-temperature co-fired ceramic (LTCC) technology due to its high permeability and relatively low sintering temperature. The main research questions regarding NiCuZn ferrites are focused on reducing the sintering temperature of the NiCuZn ferrites to achieve compatibility with the Ag electrodes and improve their electromagnetic properties. In this study, the electromagnetic properties of NiCuZn (Ni_0.29Cu_0.14Zn_0.60Fe_1.94O_3.94) ferrites were enhanced by doping with Bi₂O₃, resulting in a reduction of the sintering temperature to 925 °C. The findings show that a suitable concentration of Bi₂O₃ doping could promote the growth of grains and result in NiCuZn ferrites with denser microstructures sintered at a low temperature. Furthermore, adding 0.30 wt% Bi₂O₃ to NiCuZn ferrite enhances its electromagnetic properties, such as a high real part of permeability (～937.6 @ 1 MHz), high saturation magnetization (～60.353 emu/g), low coercivity (～0.265 kA/m), and excellent dielectric constant (～14.71 @ 1 MHz). In addition, the chemically compatible Ag electrodes suggest that the NiCuZn +0.30 wt% Bi₂O₃ ceramics may be acceptable for LTCC technology.     

The effects of surface spin on magnetic properties of weak magnetic ZnLa0.02Fe1.98O4 nanoparticles

In order to prominently investigate the effects of the surface spin on the magnetic properties, the weak magnetic ZnLa_0.02Fe_1.98O₄ nanoparticles were chosen as studying objects which benefit to reduce as possibly the effects of interparticle dipolar interaction and crystalline anisotropy energies. By annealing the undiluted and diluted ZnLa_0.02Fe_1.98O₄ nanoparticles at different temperatures, we observed the rich variations of magnetic ordering states (superparamagnetism, weak ferromagnetism, and paramagnetism). The magnetic properties can be well understood by considering the effects of the surface spin of the magnetic nanoparticles. Our results indicate that in the nano-sized magnets with weak magnetism, the surface spin plays a crucial rule in the magnetic properties.     

Influence of Al2O3 addition on microstructure,defects level and magnetic properties of LiTiZn ferrite ceramics

In the present work, the results of the influence of diamagnetic additives on the defects level of ferrite ceramics, its microstructure and magnetic properties are presented. A method based on a mathematical analysis of the experimental temperature dependences of the initial permeability was used for estimation of the defects level in the samples. Model samples containing a controlled amount of the diamagnetic additive Al₂O₃ served to test the possibility of monitoring this method of nonmagnetic phases of ferrite ceramics. It was shown that with an increase in the concentration of the Al₂O₃ additive in the range of (0–0.5) wt%, a significant increase in the defects level was observed almost 6-fold. The data from SEM micrographs showed that the addition of Al₂O₃ affects the type of grains of ferrite ceramics, but does not affect their grain size. Grains are highly agglomerated and show large grain size dispersion and also pore. Obtained data were compared to hysteresis loop parameters. It is shown that with an increase in the concentration of the Al₂O₃ addition, there is a regular decrease in the residual induction and an increase in the coercive force. However, such changes in hysteresis loop parameters are small in comparison to defects level. Investigations of the true physical broadening of the diffraction reflections were performed for the same model samples in order to compare the change in the defects level to the direct X-ray diffraction measurements of micro deformations. The defects level as a characteristic of the elastic stress of a ferrite ceramics is proposed. This assumption follows from a linear relationship between the defects level and the width of the diffraction reflections. The consistency of the obtained results made it possible to evaluate the high efficiency and sensitivity of the method for defects level estimating.     

The impact of the addition of Bi2Te3 nanoparticles on the structural and the magnetic properties of the Bi-2223 high-Tc superconductor

The polycrystalline granular BSCCO high T_c superconductors (HTSC) have limitations in various applications. These limitations appear due to the flux pinning's weakness and the weak links between the grains comparatively in high temperatures and high applied magnetic fields. Bi₂Te₃ nanoparticles are artificially introduced into the Bi-2223 HTCS matrix to be employed as effective flux pinning centers to enhance the flux pinning capability and the critical current density. The effect of the additive of Bi₂Te₃ nanoparticles on the structural and physical properties of Bi-2223 were investigated for the polycrystalline (Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ)_1-x/(Bi₂Te₃)_x where (x = 0.00,0.01,0.02& 0.03). The phase structure/formation, volume fraction, the lattice constants were described by X-ray powder diffraction (XRD) measurements. Diamagnetic signal has been investigated with two onset temperatures (T_c1&T_c2) for the common BSCCO phases (Bi-2223 and Bi-2212) which confirm the XRD obtained data without any indication for unwanted impurities. The magnetic interactions between Bi₂Te₃ nanoparticles addition and the superconductor matrix are discussed at 5 and 50 K. The relation between the microstructure, BSCCO phase's contents, the hysteresis loops, the calculated critical current densities, and the flux densities were also reported for the samples. Nano-Bi₂Te₃ shows a great impact on the BSCCO superconducting properties and influences its flux densities and the flux pinning mechanisms as reported experimentally and theoretically. Consequently, the additive of Bi₂Te₃ nanoparticles must be carefully controlled to balance the microstructure and superconducting parameters of the BSCCO HTSC.     

Al_2O_3对硼硅酸铅钙系玻璃性能的影响

用熔融法制备CaO-PbO-B2O3-SiO2系玻璃,以低温共烧法制备玻璃烧结体,研究不同Al2O3含量和烧成温度对玻璃的烧结性能和电性能的影响。结果表明:随着Al2O3含量的增加,玻璃的玻璃化转变温度升高,介电常数增加,介电损耗增加;X线衍射分析(XRD)显示G1玻璃在800℃析出CaSiO3和β-SiO2;G1玻璃于725℃保温30 min烧结,于10 MHz测试,介电常数(εr)=6.1,介电损耗(tanδ)=5.9×10-4;该玻璃有较低的玻璃化转变温度(tg=697.1℃)、较差的析晶能力、较低的介电损耗,适合作为低温共烧陶瓷(LTCC)的玻璃料使用。     

Effects of a non-magnetic CuZn ferrite layer on cofiring and electrical properties of a low-fire,multilayer NiCuZn ferrite inductor

Stress development during cofiring a bi-layer laminate with a non-magnetic (Cu_0.2Zn_0.8O)–(Fe₂O₃)_0.8 (CZF) and a magnetic (Ni_0.25Cu_0.25Zn_0.5O)–(Fe₂O₃)_0.75 (NCZF) ferrite layer has been investigated by measuring camber development and shrinkage rate difference. Development of camber follows a similar trend to that of linear shrinkage rate difference between CZF and NCZF. The sintering mismatch stress generated during cofiring is much less than those of sintering potentials, resulting in no cofiring defects observed at the interface of CZF/NCZF. Results of electrical and magnetic property measurements show that the multilayer NCZF inductor with an embedded CZF layer has a lower electrical resistance at high frequencies and less significant magnetic inductance reduction with increasing DC current than those of a pure multilayer NCZF inductor.     

The effects of Barium Strontium Titanate (BST) on the soft magnetic properties and loss performance of MnZn ferrites

With the increasing power density of the switched mode power supply (SMPS) developed nowadays, higher efficiency is required from the magnetic core, where the MnZn ferrites are often adopted. However, the relatively high operating temperature of the SMPS often results in reduced resistivity of the MnZn, which increases the eddy current loss. To enhance the resistivity of MnZn ferrite at high temperature range (>100 °C), donor-doped barium strontium titanate (BST) with a positive temperature coefficient of resistivity (PTCR) is prepared and dopped in the MnZn ferrite. The influence of BST addition from 0.000 wt% to 0.020 wt% on the MnZn ferrite is investigated over a wide temperature range from 25 °C to 140 °C. The XRD result suggests ionic exchange between the spinel phase and perovskite phase. The SEM result shows a refined and more uniform microstructure of MnZn ferrite brought about by the BST addition. At the maximum of 0.020 wt%, the BST addition shows almost no influence on density and the saturation magnetic induction. However, the initial permeability is slightly reduced by the BST addition, due to the microstructural change. Moreover, the BST concentrating at the grain boundaries improves the DC-resistivity across the temperature range from 25 °C to 140 °C. Due to the addition of BST, the reduction in eddy current loss at 300kHz/100 mT is around 35% at 25 °C, and ∼20% reduction at 140 °C.