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In order to adjust the initial permeability and the dielectric constant for suppressing electromagnetic interference (EMI), a series of the composites with Pb_0.95Sr_0.05(Zr_0.52Ti_0.48)O₃ (PZTS) powders and NiCuZn ferrite (NCZF) powders as raw materials were synthesized by a solid-state reaction method. The effects of different PZTS content on the sintering behaviors, phase composition, microstructures and electromagnetic properties of the composites co-fired at 900°C were investigated. The acquired ferroelectric–ferromagnetic composites are of perovskite phase and spinel phase, exhibiting both capacitance and inductance properties and excellent frequency stability due to the mutual effects of magnetization of NCZF phase and the polarization of PZTS phase. As PZTS content increased, the initial permeability and the saturation magnetism (B_m) decreased gradually, the coercive force (Hcb) and the quality factor (Q) increased, the resonance frequency shifts toward a higher frequency. Simultaneously, the dielectric constant evidently increased with PZTS content when x varied from 0 to 50wt%. A maximum Q-factor (50), a maximum dielectric constant (80), a higher DC resistivity (4.96×10¹⁰Ωm), a higher ferromagnetic resonance frequency (over 1.8GHz) and a relatively higher initial permeability (5–7) were obtained for the composite with 50wt% PZTS.

▼ In this work, we studied the substitution effect of iron by gallium on the structural, magnetic and electrical properties of the ferrite system; Ni_0.5Cu_0.25Zn_0.25Fe_2-xGa_xO₄ (x=0-1.0), synthesized by using the urea combustion method. XRD patterns of the samples calcined at 700^oC show only cubic spinel ferrite with an average crystallite sizes in the range of 40-54nm. The lattice parameters were slightly changed with increasing Ga content which can be explained on the basis of the relative ionic radii of Ga^3^+ and Fe^3^+ ions. FT-IR measurements show two fundamental absorption bands, assigned to the vibration of tetrahedral and octahedral complexes, which were slightly changed with increasing Ga content. Mossbauer measurements enable us to predict the possible cation distribution of the system. It was found that Ga^3^+ ion prefer to substitute Fe^3^+ ions located in the octahedral site. Superparamagnetic state was observed in the Mossbauer spectra of the samples with Ga content >0.5. The decrease of the magnetic hyperfine field with gallium concentration was explained on the basis of supertransferred hyperfine interaction. A semiconducting behavior was inferred for all samples and the conductivity values were found to decrease with increasing the Ga content. The conduction mechanism in the spinel ferrite compounds was explained in terms of the hopping conduction process. The dielectric constant measured as a function of frequency and temperature was found to be dependent on the Ga concentration. The determined transition temperature was found to decrease with increasing Ga content.

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Ni_0.25Cu_0.2Zn_0.55Sm_xFe_2−xO₄ ferrite with x=0.00, 0.025, 0.05 and 0.075 compositions were synthesized through the nitrate–citrate auto-combustion method. These powders were calcined, compacted and sintered at 900°C for 4h. Effect of Sm substitution on phase composition, microstructure and relative density were studied. Permeability, magnetic loss and AC resistivity were measured in the frequency range of 1kHz–10MHz. Permeability and AC resistivity were found to increase and loss decreased with Sm substitution up to x=0.05. Saturation magnetization also increased up to that substitution limit. Observed variations in electromagnetic properties have been explained.

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Ni–Cu–Zn ferrites have been synthesized by employing co-precipitation technique using oxalate precursors. X-ray diffractograms did not show impurity phases, indicating single-phase formation of the ferrites. The diffractograms of oxalate complex decomposed at 650°C show that ferritization is complete up to 650°C. Lattice parameter a (Å) was found to decrease with the addition of Ni²⁺ which is attributed to ionic sizes of Ni²⁺ (0.69Å), which replaces Cu²⁺ (0.72Å). From the thermogravimetric studies it is observed that the experimentally observed total mass loss (%), agrees with theoretically calculated mass loss (%) indicating maintenance of requisite stoichiometry. Initial permeability (μ_i ) shows increase when Ni²⁺ is added up to Formula Not Shown while for ( Formula Not Shown ), it decreases. The increase in initial permeability (μ_i) is attributed to monotonic increase in Ms, and K₁ on addition of Ni²⁺. However, the microstructure and density (porosity) also influence μ_i variations. The decrease in μ_i is attributable to increase of K_1. The composition with density 91.14% exhibits large μ_i which also tends to increase with temperature up to 60°C. Thus its usable range extends up to 60°C. This samples has T_c near to 160°C.

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The ferrite compositions of (Ni_0.25−xMg_xCu_0.2Zn_0.55)Fe₂O₄ with Formula Not Shown , 0.07, 0.13, 0.18, and 0.25 were synthesized through nitrate-citrate auto-combustion method. The as-burnt powders showed the presence of crystalline cubic spinel ferrite with about 19–22nm crystallite sizes. The resultant powders were calcined at 700°C/2h and pressed ferrites were sintered at 950°C/4h. The initial permeability, magnetic loss and AC resistivity were measured in the frequency range 10Hz–10MHz. The permeability and AC resistivity were found to increase and the magnetic loss decreased with Mg substitution for Ni, up to Formula Not Shown . The very high permeability in the composition Formula Not Shown , was due to better densification, lower magnetostriction constant and inner stresses, etc. The AC resistivity of the composition was also highest. The composition would be better than NiCuZn-based material for more miniaturization of multi layer chip inductor.

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Nanocrystalline Mg-substituted NiCuZn ferrites were successfully synthesized, for the first time, by using metal nitrates and freshly extracted egg white. The thermal decomposition process of the nitrate–egg white precursors was investigated by thermogravimetric (TG) technique. X-ray diffraction (XRD) revealed that, single-phase cubic ferrites with average particle size of 23.9–35.1nm were directly formed after ignition at 500°C. No noticeable variation of lattice parameters with increasing magnesium content was observed, while X-ray densities were found to decrease. This can be explained on the basis of ionic radii and atomic masses of the substituted cation. Transmission electron microscope (TEM) shows that, particles are permanently magnetized and get agglomerated. The saturation magnetization (M_s) and coercivity (H_c) as a function of Mg content were investigated using vibrating sample magnetometer (VSM). It has been found that the M_s increases firstly up to x=0.2 and then decreases, while H_c continuously decreases. Magnetic susceptibility measurements give results which agree well with those obtained by VSM. The obvious decrease in the Curie temperature (T_C) with increasing Mg indicates that the ferrimagnetic grains are widely separated and enclosed by non-magnetic magnesium ions.

▼ This paper examines the effect of copper substitution on the structural and magnetic properties in nano-crystalline ferrite series of nominal composition; Ni_0.7-xCu_xZn_0.3Fe₂O₄ (where x=0.1-0.6) synthesized by a simple method using metal nitrates and freshly extracted egg-white. X-ray diffraction measurements (XRD) confirmed the formation of single-phase cubic spinel structure. The average crystallite size was calculated using XRD pattern and confirmed by transmission electron microscope (TEM). The nearly constant lattice parameters obtained with Cu substitution was attributed to the small difference in the ionic radius between Ni^2^+ and Cu^2^+ ions. FT-IR spectra showed two absorption bands assigned to the tetrahedral and octahedral complexes. The effect of Cu concentration on the magnetic properties was investigated using vibrating sample magnetometer (VSM) and molar magnetic susceptibility measurements. The decrease in the saturation magnetization and the Curie temperature values with increasing Cu content was explained in terms of the magnetic moments and magnetic exchange interaction existing between the antiparallel uncompensated electron spin of A and B sublattices. The magnetic measurements also proved that the entire preparation method has a great effect on enhancing the magnetic properties of the system.

▼ Nanocrystalline ferrites of compositions Ni_0.5+1.5xCu_0.3Zn_0.2Fe_2-xO₄ (0 x 0.5) have been synthesized by using oxalate based precursor method at very low temperature. The Ni-Cu-Zn ferrite powder particles were obtained at 450^oC and they exhibit a crystallite size of 16-24nm. The lattice constants were found nearly equal in all these samples due to minute difference in the ionic radius between Ni^2^+ and Fe^3^+ ions. The thermal analysis has showed the ferrite phase formation at very low temperature 377^oC. The two main spectroscopic bands corresponding to lattice vibrations were observed in the wavelength range from 300 to 1000cm^-^1. The IR bands at 570cm^-^1 (v₁) and 390cm^-^1 (v₂) were assigned to tetrahedral (A) and octahedral [B] groups. The spectroscopic bands shift with the increase of doping concentration. The magnetization was found to decrease with increasing doping concentration. The dielectric constant ( ') and dielectric loss tangent (tanδ) decreased with increase of frequency. The dielectric constant and dielectric loss obtained for the nanocrystalline ferrite samples appeared to be lower than that of the ferrites prepared by other synthesis techniques.

▼ 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^oC for 2h showed single-phase crystalline cubic ferrites with crystallite sizes in the range 17.2-21.6nm. 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 Fe^3^+-O^2^-, 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 Fe^3^+-Fe^3^+ 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 La^3^+ ions decreases the ferromagnetic region at the expense of the paramagnetic one.

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In this paper, the effect of Mn³⁺ doping on the high- and low-frequency electromagnetic properties of NiCuZn-ferrites is investigated. There is an optimum Mn³⁺ concentration at which low-frequency properties such as initial permeability and power losses attain maximum and minimum values, respectively. Simultaneously, the high-frequency losses increase. This optimum Mn³⁺ concentration is found to depend on iron deficiency of material composition. The low- and high-frequency behaviors of the material are found to be very consistent with the characteristics of the microstructure. An explanation according to which manganese, when added at concentrations where the total trivalent cation amount of the material remains slightly below stoichiometry (i.e. Fe³⁺+Mn³⁺⩽2), acts as grain growth promoter is proposed. At higher concentrations, the fill of the cation vacancies depresses grain growth and results to fine microstructures, which is negative for the low-frequency but positive for the high-frequency properties.

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Iron rich, stoichiometric iron and iron deficient samples of NiCuZn ferrite were prepared by conventional ceramic double sintering process. The formation of single phase was confirmed by X-ray diffraction. Initial permeability measurements on these samples were carried out in the temperature range of 30–400°C. The effect of external applied stress on the open magnetic circuit type coil with these ferrites was studied by applying uniaxial compressive stress parallel to the magnetising direction and the change in the inductance was measured. These studies show that stress sensitivity is more in the case of iron rich and stoichiometric iron samples while in the case of iron deficient samples the stress sensitivity was found to be less.

▼ For the purpose of multilayer chip electromagnetic interference (EMI) filters, a series of xBa_0.6Sr_0.4TiO₃ (BST)+(1-x)Ni_0.2Cu_0.2Zn_0.62O(Fe₂O₃)_0.98 (NiCuZn ferrite) (0 x 60wt.%) composite ceramics were primarily prepared by a solid-state reaction method. With addition of 3wt.% Bi₂O₃, all the composite ceramics can be sintered to a density >95% of theoretical density at 925^oC. The effects of composition x on the sintering behaviors, phase compositions and electromagnetic properties of BST+NiCuZn ferrite composite materials were investigated. X-ray diffraction (XRD) results showed that the composites were composed of BST and NiCuZn phases. The ions' diffusion was found to take place between NiCuZn ferrite and BST, which affected the electrical properties of the ceramics. With an increase of BST content x, the dielectric constant of the composites increases and the permeability decreases. For the specimens with 40wt.% Ba_0.6Sr_0.4TiO₃-60wt.% Ni_0.2Cu_0.2Zn_0.62O(Fe₂O₃)_0.98, the good dielectric ( _r=48, tanδ| =0.01) and magnetic properties (μ=20.8, tanδ|_10MHz=0.03) have been obtained at 950^oC. Meanwhile, it exhibited excellent frequency stability which was up to f_r=100MHz.

▼ The effects of Cu and Ti substitution on the sintering behavior, substitution mechanism, resistivity and dielectric properties of CuZn ferrites were investigated. Codoped Cu^2^+ and Ti^4^+ can effectively reduce the densification temperature of copper zinc ferrite to below 900^oC and improve the resistivity and dielectric properties. The copper and titanium-codoped CuZn ferrites and NiCuZn ferrites exhibited excellent compatibilities in physical and chemical matching during cofiring. Therefore, the copper and titanium-codoped CuZn ferrites can be a good candidate material for an effective intermediate nonmagnetic layer for NiCuZn ferrites in preparing a multilayer chip inductor with a high rated current.

▼ Egg-white method was used to produce nanocrystalline Cr-substituted NiCuZn ferrites; Ni_0.50Cu_0.25Zn_0.25Fe_2-xCr_xO₄ (0.0 x 1.0) from stoichiometric mixture of their respective metal nitrate. The structural, morphological and magnetic properties of the products were determined by X-ray powder diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The average crystallite sizes obtained from XRD were between 15 and 25nm. Magnetization measurements indicated that when the Cr substitution increases the saturation magnetization decreases due to the magnetic character of the chromium ions which prefers octahedral site occupation. The coercivity was found to change proportionally with the particle sizes of the investigated ferrites.

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Dense Ni_0.37Cu_0.20Zn_0.43Fe_1.92O_3.88/(Ba_0.6Sr_0.4)TiO₃ composite thick films were prepared through screen printing method and sintered at 880°C. The powder XRD patterns confirm the coexistence of the two phases. The dielectric and magnetic properties are also reported. The results show that this kind of magnetic–dielectric composite thick films, possessing high permittivity and saturation magnetization, moderate dielectric tunability, and very low dielectric loss and coercivity, could be used in high-frequency communications for the capacitor–inductor integrating devices such as electromagnetic interference filters and antennas.

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Dense CaTiO₃/Ni_0.37Cu_0.20Zn_0.43Fe_1.92O_3.88 (CTO/NiCuZn) composites were prepared by the conventional solid-state reaction method and sintered at 950°C. The phase compositions and surface morphologies of the composites were investigated using x-ray diffraction and scanning electron microscopy, respectively. The dielectric and magnetic properties of the composites were also investigated. The results show that the CTO/NiCuZn composites possess high dielectric constants and permeabilities, which can be used in high-frequency communications for capacitor–inductor integrating devices such as electromagnetic interference filters and antennas. With increasing NiCuZn concentration, the permeabilities of the CTO/NiCuZn composites increase, while the dielectric constants and cutoff frequencies decrease.

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For the purpose of multilayer chip EMI filters, the new ferroelectric–ferrite composite ceramics were prepared by mixing PMZNT relaxor ferroelectric powder with composition of 0.85Pb(Mg_1/3Nb_2/3)O₃–0.1Pb(Ni_1/3Nb_2/3)O₃–0.05PbTiO₃ and NiCuZn ferrite powder with composition of (Ni_0.20Cu_0.20Zn_0.60)O(Fe₂O₃)_0.97 at low sintering temperatures. A small amount of Bi₂O₃ was added to low sintering temperature. Consequently, the dense composite ceramics were obtained at relative low sintering temperatures, which were lower than 940°C. The X-ray diffractometer (XRD) identifications showed that the sintered ceramics retained the presence of distinct ferroelectric and ferrite phases. The sintering studies and scanning electron microscope (SEM) observations revealed that the co-existed two phases affect the sintering behavior and grain growth of components. The electromagnetic properties, such as dielectric constant and initial permeability, change continuously between those of two components. Thus, the low-temperature sintered ferroelectric–ferrite composite ceramics with tunable electromagnetic properties were prepared by adjusting the relative content of two components. These materials can be used for multilayer chip EMI filters with various properties.

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Low Mn-doped NiCuZn ferrites with compositions of (Ni_0.6Zn_0.3Cu_0.1)_1−xMn_xFe₂O₄ (where x=0, 0.01, 0.02 and 0.03) were synthesized directly with sol–gel method. The influence of the Mn²⁺ content (parameter x) and the sintered temperature on the microstructure and the magnetic properties of these ferrites were mainly discussed. With the increasing Mn²⁺ content, saturation magnetization (M_s) of the powder samples decreased. Saturation magnetic flux density (B_s) and remnant magnetic flux density (B_r) of the toroidal specimens decreased with the Mn²⁺ content up to x=0.02, followed by increasing. B_r and B_s both increased with the increasing sintered temperature, while coercivity (H_c) decreased. The real part of permeability (μ′) of the toroidal specimens increased up to x=0.01, followed by decreasing. The sintered temperature also affected the resonance frequency and the useable frequency (from which the value of tanδ increased more) obviously. Furthermore, the low-frequency permeability and the secondary maximum (the maximum of the permeability appearing the secondary time) both increased with the sintered temperature from 70 to 120 and 150 to about 600.

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Mn-doped NiCuZn ferrites with compositions of (Ni_0.2Cu_0.2Zn_0.6)O(Fe_2−x,Mn_xO₃)_0.98 (x=0, 0.02, 0.04, 0.06) were prepared by a novel sol–gel auto-combustion process. The synthesized nano-sized ferrite powders can be sintered at 900°C, and the sintered ferrites are characterized by fine-grained microstructural feature and high permeability. Mn content in formulations largely affects the grain size and main electromagnetic properties of sintered NiCuZn ferrites. With increasing Mn content, the initial permeability is significantly increased, while the electrical resistivity and quality factor are decreased. The dielectric constant and dissipation factor are also affected by the incorporation of MnO₂. The possible mechanism for the influence of MnO₂ on the electromagnetic properties was discussed.

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In this study, nano-sized ferrites of compositions (Ni_0.6Cu_0.20Zn_0.20Fe_2−xCr_xO₄), where x=0–1.0, were synthesized through nitrate–citrate auto-combustion method at relatively low temperature. XRD revealed the formation of nano-sized ferrite particles with cubic spinel structure. An exception was obtained for samples with Cr content ≤0.2, where weak diffraction peaks attributed to the presence of CuO and Fe₂O₃ were appeared. The average crystallite sizes are much dependent on the chromium content and were found to decrease with its increase. The lattice parameter (a) slightly decreases with Cr substitution, which can be explained on the basis of the relative ionic radii of Cr³⁺ and Fe³⁺ ions. X-ray density was found also to decrease slightly with increase in chromium content, which indicates lower densification by the addition of Cr. FT-IR measurements show the characteristic ferrite bands. The Mössbauer spectra varied from Zeeman sextets to a relaxed doublet by increase in Cr content, which indicates a decrease in the hyperfine field at the octahedral site. Electrical property measurements revealed that Cr³⁺ ions do not participate in conduction process but limit the degree of Fe³⁺–O²⁻–Fe³⁺ conduction resulting in a decrease in the conductivity and increase in conduction activation energy.

▼ Ni_0.23Cu_0.11Zn_0.66Fe₂O₄ nanowire arrays were fabricated by a simple ethanol-nitrate method using anodic aluminum oxide (AAO) templates. XRD result indicated that the nanowires are of cubic spinel structure. SEM and VSM were used to characterize morphology and magnetic anisotropy properties of the nanowire arrays, respectively. It is believed that this method should be applicable to other multi-component oxide nanowires.

▼ Ni_0.23Cu_0.11Zn_0.66Fe₂O₄ ferrite flakes, with thickness of about 8μm and average diameter of 20-35μm, were prepared using a sol-gel bubble method. Morphology, phase evolution, static and dynamic magnetic properties of the flakes and their composites were studied. Magnetic measurements showed that easy magnetization direction of the flaky filler composite was parallel to its sample plane. Composites made of silicone resins and flakes had higher complex permeability, which can be attributed to the reduction in demagnetization factor due to their flaky shapes. This sol-gel bubble method should be also applicable to fabricating flakes of other multi-component oxides.

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Ni_0.5−xCu_xZn_0.5Fe₂O₄ (0.0≤x≤0.5) ferrite nanofibers with diameters of 80–160nm have been prepared by electrospinning and subsequent heat treatment. Both the average grain size and lattice parameter are found to increase with the addition of copper. Fourier transform infrared spectra indicate that the portion of Fe³⁺ ions at the tetrahedral sites move to the octahedral sites as some of the substituted Cu²⁺ ions get into the tetrahedral sites. Vibrating sample magnetometer measurements show that the coercivity of these ferrite nanofibers decreases with increasing Cu concentration, whereas the specific saturation magnetization initially increases, reaches a maximum value at x=0.2 and then decreases with the Cu content further increase. Notable differences in magnetic properties at room temperature (298K) and 77K for the Ni_0.3Cu_0.2Zn_0.5Fe₂O₄ nanofibers and corresponding powders are observed and mainly arise from the grain size and morphological variations between these two materials.

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The morphology of Ni-Cu-Zn ferrite powders obtained by milling of a calcined raw materials mixture strongly effects the densification behavior during sintering at 900^∘C. In order to obtain dense samples sub-micron powders with enhanced reactivity are required. The addition of Bi₂O₃ as sintering additive is beneficial: the density of samples sintered at 900^∘C increases with the bismuth oxide concentration up to 0.75 wt.%. The process of liquid phase sintering was studied by dilatometry. The grain size of the sintered samples slightly increases for 0.25 wt.% Bi₂O₃ compared to bismuth-free samples, whereas for 0.3–0.5 wt.% Bi₂O₃ additions bimodal grain growth is observed with a significant fraction of very large grains. For > 0.5 wt.% Bi₂O₃ a homogeneous coarse-grained microstructure is obtained. The permeability increases for small bismuth oxide additions, but decreases for a Bi-oxide content of more than 0.5%. Maximum permeability of μ_i = 900 is observed for intermediate Bi₂O₃ concentrations.

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Ni-Cu-Zn ferrites of composition Ni_{1 − x − y}Cu_yZn_xFe₂O₄ with 0.4 ≰ x ≰ 0.6 and 0 ≰ y ≰ 0.25 were prepared by standard ceramic processing routes. The density of samples sintered at 900^∘C increases with copper concentration y. Dilatometry reveals a significant decrease of the temperature of maximum shrinkage with y. The permeability has maximum values of μ = 500–1000 for x = 0.6. The Curie temperature is sensitive to composition and changes form about 150^∘C for x = 0.6 to T_c > 250^∘C for x = 0.4, almost independent on the Cu-content. A small iron deficiency in Ni_0.20Cu_0.20Zn_{0.60 + z}Fe_{2 − z}O_{4 − (z/2)} with 0 ≰ z ≰ 0.06 significantly enhances the density of samples sintered at 900^∘C. The maximum shrinkage rate is shifted to T < 900^∘C. These compositions are therefore appropriate for application in low temperature co-firing processes. The permeability is reduced with z, hence a small z = 0.02 seems to be the optimum ferrite composition for high sintering activity and permeability.

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In the present work, ferrites with compositions of (Ni_0.27Zn_0.64Cu_x)Fe_1.98O₄ (x=0.1, 0.2) were prepared by conventional ceramic methods. The relationship between the microstructure and the temperature dependence of relative initial permeability was investigated. It was found that intergranular pores in the ferrites generate large demagnetizing fields, reducing the temperature dependence of the effective anisotropy field H_eff, and decreasing the temperature dependence of the relative initial permeability accordingly. However, intragranular pores pin the movement of domain walls. Compared with the permeability induced by domain wall motion, the permeability that resulted from the spin rotation is more sensitive to temperature. As a result, the relative initial permeability of ferrites becomes more sensitive to temperature with increasing micropores within grains.

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This work investigated the concentration dependence of the nanosized Ni fillers on crystallographic structure, electrical transport, effective permeability, constitutive electromagnetic property, and microwave-absorbing behavior of the insulating polymer matrix embedded with NiCuZn ferrites (NCZFs). The effective permeability of the percolation ferrite composites which are composed of three-phases, 0.55 NCZF/(x) nano Ni/(0.45-x) polymer, increases with x till x=0.1. It is due to the Ni fillers acting as magnetic bridge to enhance magnetic exchange coupling and to decrease the demagnetization field between ferrite granules. The electrical resistivity decreases abruptly above the percolation threshold (x=0.02). It is ascribed to the narrowed polymer gaps and the significant decrease in the grain boundary resistance after the Ni additions. The frequency response of the microwave absorption in ferrite composites is attributed to its macroscopic magnetic loss and dielectric loss correlated with domain-wall motion, spin resonance, and dipolar relaxation. Various multilayer microwave absorbers terminated by perfect metal conductor (PMC) are systematically designed utilizing the constitutive electromagnetic properties of ferrite composites. When the Ni concentration is increased, the microwave return loss is greatly enhanced and the absorption band becomes narrower towards the lower frequency. The maximal return loss of single-layer absorbers composing of 7.2mm-thick ferrite composites with x=0.15 is estimated as −53.9dB with an absorption bandwidth 1.72GHz. Due to the decreasing products of matching thickness and frequency at maximal return loss, the incorporation of Ni fillers in ferrite composites facilitates to reduce the absorber thickness. Additionally, the microwave absorbing behaviors of double-layer microwave absorbers with different lamination sequences of Ni-encapsulated ferrite composites were also investigated.

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We have fabricated the planar micro-inductors directly on a NiCuZn ferrite substrate. Due to NiCuZn’s high resistivity, no insulator is required between the coil and the magnetic film; an advantage in terms of ease fabricated and stray capacitance reduction. Sandwiched inductors show improvement of inductance from 16 to 80nH at 1MHz compared with the coreless inductors, and the increment of inductance is larger than the sandwiched thin film inductor.

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Free-standing Ni_0.23Cu_0.11Zn_0.66Fe₂O₄ thick films have been prepared using a modified tape-casting method from a viscous paint. The surface morphology, saturation magnetization (M_s), coercivity (H_c) and complex permeability of the thick films were studied. It is demonstrated that the thick films have relatively larger complex permeability and higher resonance frequency as compared to their bulk material counterparts.

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We studied the effects of iron-deficient, stoichiometric and iron-excessive compositions on the phase formation, crystal structure, grain growth and magnetic property of NiCuZn ferrites. As the Fe₂O₃ ratio increased from iron-deficiency 47.0mol% to iron-excess 54.0mol%, the X-ray diffraction peaks initially shifted towards lower angle and then moved to higher angle. Correspondingly, an initial increase in lattice parameter followed by a subsequent decrease was observed. The lattice parameter showed a maximum 8.396Å when the Fe₂O₃ ratio was 49.0mol%. When the system was iron-deficient, ZnO phase was detected in addition to the spinel phase. However, equimolar and iron-excessive compositions exhibited a single spinel phase. As the content of Fe₂O₃ increased, the grain size, density, saturation induction and initial permeability first increased and then decreased. Core losses at 50kHz and 150mT, however, changed in the opposite way. Finally, NiCuZn ferrite with an equimolar composition (50.0mol%) showed the highest initial permeability (1467), highest saturation induction (361mT) and lowest core losses (234kW/m³).