NiCuZn Ferrites Research Articles

Effects of Li2CO3 addition on the microstructure and magnetic properties of low-temperature-fired NiCuZn ferrites

NiCuZn ferrites doped with 0.5wt% Bi2O3 and different Li2CO3 contents (0–0.25wt%) were sintered at 900°C. The microstructure and magnetic properties of these materials were investigated. The addition of low-melting-point Li2CO3 led to large and uniform grains. However, excess Li2CO3 addition produced abnormal grains and many closed pores, thereby reducing density. Permeability initially increased and then decreased at the Li2CO3 content of >0.2wt%. Maximum magnetic flux density (431.1mT at room temperature, 339.6mT at 100°C) and minimum power loss were achieved at 0.2wt% Li2CO3. These findings suggested the suitability of 0.2wt% Li2CO3 for applications in low-temperature co-fired ceramic magnetic power components and modules.

Effects of Co2O3 concentration on high Q-factor NiCuZn ferrites for 13.56 MHz radio identification communication

Co2O3-doped NiCuZn ferrites with a high (group A) or low (group B) permeability were prepared using the conventional ceramic method to obtain high Q-factor NiCuZn ferrites for a 13.56MHz near-field-communication (NFC) system. The XRD patterns of samples from both groups exhibited single spinel phase. Permeability monotonously decreased with increasing Co2O3 content, whereas sintering density and saturation magnetic flux density (Bs) slightly changed with Co2O3 content. The permeability of 0.45wt% Co2O3-doped ferrite (A0.45) was similar to that of 0.10wt% Co2O3-doped ferrite (B0.10). However, the former sample presented a considerably higher Q-factor than the latter sample. The former sample also presented enhanced stability variation of Q-factor with frequency, which indicated an improved electromagnetic shielding function for the NFC system. The mechanisms involved were also elucidated.

Rietveld refinement, microstructure and ferromagnetic resonance linewidth of iron-deficiency NiCuZn ferrites

Ni0.56+x/2Zn0.34Cu0.1Fe2.0-xO4-x (x = 0, 0.02, 0.04, 0.06, 0.08, 0.12) ferrites have been prepared by the solid-state reaction method. The Rietveld refinement of X-ray diffraction patterns, microstructure, static magnetic properties and ferromagnetic resonance (FMR) linewidth of NiCuZn ferrites have been analyzed by X-ray diffraction, scanning electron microscopy (SEM), B-H analyzer and electron spin resonance (ESR) spectrometer, respectively. The FMR linewidth was investigated by an approximate calculation based on spin wave approach. The results revealed that all the samples were a single NiCuZn spinel phase. With the increase of iron-deficient amount, the lattice parameter (a) displayed a decreasing trend. However, the bulk density first increased rapidly and then trended to go up slightly. The saturation magnetization of stoichiometric NiCuZn ferrites was much lower than that of iron-deficient samples. This phenomenon is ascribed to the combined effect between molecule magnetic moment and bulk density. The magnetocrystalline anisotropy constant, derived from the law of approach to saturation, has been discussed. The anisotropy and porosity linewidth broadening models were adopted to identify the linewidth contribution. The results manifested that the porosity linewidth broadening was much larger than the anisotropy linewidth broadening.

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.

Microwave sintering versus conventional sintering of NiCuZn ferrites. Part I: Densification evolution

This work reports the recent study on the microwave sintering (MS) versus conventional sintering (CS) of NiCuZn ferrites, with particular interests in the densification evolution. NiCuZn ferrite powders were synthesized through the solid state reaction route. Densification behaviors of ferrite samples under the two types of thermal sources were monitored in real-time. Meanwhile, the influences of additives (1wt% BSZ glass or 1wt% Bi2O3) on the densifications were also investigated. Both constant heating rate (CHR) and master sintering curve (MSC) models were used to evaluate the sintering activation energy (Q). Results demonstrated that the microwave-enhanced diffusion mainly occurs at the intermediate sintering stage. The Q-value estimated by MSC method agreed well with that from CHR method. With the influence of microwave electromagnetic field, the activation energy of NiCuZn ferrites was decreased by roughly 100–150kJ/mol. In addition, doping a small amount of additives could improve densification degree and reduce the minimal energy to activate diffusion mechanisms.

Microwave sintering versus conventional sintering of NiCuZn ferrites. Part II: Microstructure and DC-bias superposition characteristics

NiCuZn ferrites with the composition of (Ni0.48Cu0.10Zn0.42O)1.04(Fe2O3)0.96 were consolidated by microwave sintering (MS) and conventional sintering (CS), respectively. The influences of external microwave field and additives (1wt% BSZ glass or 1wt% Bi2O3) on the microstructure and DC-bias superposition characteristics of NiCuZn ferrites were investigated. Experimental results demonstrated that the final grain size was much larger with higher density since applying microwave field. In addition, for undoped ferrites, coarse grains structure obtained from microwave sintering is harmful to the DC-bias superposition characteristics. However, since adding BSZ glass or Bi2O3, the discrepancy on the final grain size obtained from MS and CS methods is not obvious. NiCuZn ferrites with the addition of BSZ glass or Bi2O3 exhibited a stronger ability to inhibit the drop of permeability under the DC-bias magnetic field. Possible mechanisms behind are discussed in this article.

Ag precipitation at the free interface of multilayer NiCuZn ferrites/LTCC components

The diffusion and precipitation of silver and copper in low-dielectric-constant low temperature cofired ceramics (LTCC) for multilayer NiCuZn ferrites/LTCC components are investigated in this study. Ag precipitation is formed at the free interface between NiCuZn ferrites and LTCC for multilayer NiCuZn ferrites/LTCC components after cofiring. During the heating stage Cu+ will segregate into the grain boundary from the NiCuZn ferrites due to the low oxygen partial pressure inside the sample and then dissolve into LTCC near the interface between NiCuZn ferrites and LTCC. Cu+ in glass would diffuse from the interior toward the surface and become oxidized into Cu2+ or precipitated as the CuO phase at the surface. To maintain charge neutrality this process requires an outward diffusion of Cu+ and Ag+ from the interior toward the free surface. The reduction of Ag+ into Ag on the free surface is accelerated by Cu+ oxidation.

Influence of particle size on the magnetic spectrum of NiCuZn ferrites for electromagnetic shielding applications

The effect of ferrite particle size on the magnetic spectra (1MHz to 1GHz) of NiCuZn polycrystalline ferrites doped with Co2O3 and Bi2O3 were systematically investigated. The experiments indicate that the ferrite particle size tailored by grinding time and corresponding sintering temperatures is crucial to achieving high permeability, high Q-factor and low magnetic loss, at 13.56MHz for electromagnetic shielding applications especially in the near field communication (NFC) field. It is evident that high-performance NiZnCu ferrite materials are strongly tailored by morphology and microstructure. It is conclusive that fine ferrite particles and relatively low sintering temperatures are favorable to lowering magnetic loss and enhancing permeability. This work has built a foundation for improvement of the ferrite slurry used for fabrication of large area tape-casting ferrite sheets.

Microstructure and magnetic properties of low-temperature-fired NiCuZn ferrites with various borosilicate glasses

The low-temperature-fired NiCuZn ferrites with various borosilicate glasses were prepared by the conventional solid-state reaction method. Different weight percentages of glasses such as Al2O3–B2O3–SiO2 (ABS), Na2O–Al2O3–B2O3–SiO2 (NABS), Bi2O3–B2O3–BaO–SiO2 (BBBS) were added to low-temperature-fired NiCuZn ferrites. The effects of these glasses on sintering behavior, microstructures and magnetic properties of NiCuZn ferrites were also investigated. It is found that moderate amount of borosilicate glass addition can promote the densification and improve the magnetic properties of NiCuZn ferrites due to the formation of liquid phase, but too more liquid phase formation will deteriorate the magnetic properties. In addition, results also show that addition of BBBS glass can promote best densification of NiCuZn ferrites, but improve magnetic properties worse than addition of ABS or NABS glass. By contrast, the NiCuZn ferrite sample with 0.1 wt% ABS glass can obtain best magnetic properties: μi = 733.01 at 100 kHz, Bs = 162.39 mT, Br = 86.59 mT and Hc = 35.7 A m−1.

Structure, morphology, and magnetic properties of high-performance NiCuZn ferrite**Project supported by the National Natural Science Foundation of China (Grant Nos. 11174132, 11474151, and U1232210), the National Key Project for Basic Research, China (Grant Nos. 2011CB922102 and 2012CB932304), the Innovation Program for Doctoral Research of Jiangsu Province, China (Grant No. CXZZ13_0035), and the Priority Academic Program Development of Jiangsu Provincial Higher

High-performance submicron-scaled NiCuZn ferrites are prepared by the solid-state reaction method through using CuO as additive. In the synthesis process, a mixture of superfine powder is sintered at 900 °C for 3 h, and the obtained product is NiZn-ferrite with spinel structure. We observe that the particle size increases with raising the sintering temperature. The NiCuZn ferrite with relatively uniform size and granular shape has the best performance: its coercivity is 14 Oe (1 Oe=79.5775 A·m−1) and saturation magnetization is 48 emu/g. We also study the effects of particle size, magnetocrystalline anisotropy, and microstructure on coercivity. The method presented here is convenient and economical for producing the high-permeability ferrite powders.

Microstructure and magnetic properties of low-temperature-fired NiCuZn ferrites with SiO2–CaO–Na2O–K2O glass

The low-temperature-fired NiCuZn ferrites with SiO2–CaO–Na2O–K2O (SCNK) glass additives are prepared by the conventional solid-state reaction method. The effects of SCNK glass additives on sintering behavior, microstructures and magnetic properties of NiCuZn ferrites are also investigated. Results show that SCNK glass additives overtly improve the densification of samples through the formation of liquid phase and grains growth promotion. The appropriate SCNK glass additives not only can noticeably increase the initial permeability (μi) and saturation flux density (Bs), but also can obviously reduce the remanent flux density (Br) and coercive filed strength (Hc). However, too much glass additives will deteriorate the magnetic properties. In summary, 0.2 wt% SCNK glass added in NiCuZn ferrite shows excellent magnetic properties: μi = 648.18 (100 kHz), Bs = 166.21 mT, Br = 83.57 mT and Hc = 39.38 A m−1.

Key Technology and Materials for the Development of DC-DC Converter Module

Portable devices are often powered by batteries and DC-DC converters are used to convert battery energy to supply power for microprocessors and integrated circuits. Portable electronic devices are required to be compact and, hence, space for converters is very limited. Therefore, the demand for integrating individual components into modules to reduce the size and increase the power density of DC-DC converters is increasing. It is important to develop a low temperature sintering NiCuZn ferrites with a superior DC-bias-superposition characteristic; the nonmagnetic materials co-fired with the magnetic NiCuZn ferrites, and the low-pressure assisted constrained sintering process for the large area NiCuZn ferrites substrates for the DC-DC converter modules. This study successfully developed the key technologies and materials for the development of DC-DC converter module. It integrated the magnetic NiCuZn ferrites with superior DC-bias superposition characteristic and nonmagnetic ferrite materials using multilayer ceramic processing and low-pressure assisted constrained sintering technologies to prepare a large area NiCuZn ferrite substrate for DC-DC converter module.

Monodomain Design and Permeability Study of High-Q-Factor NiCuZn Ferrites for Near-Field Communication Application

For application in near-field communication (NFC) systems, monodomain NiCuZn ferrite has been prepared by the conventional solid-state reaction method. The results show that the monodomain design is effective; the Q factor of this kind of sample with 0.3 wt.% Co2O3 doping could be as high as 118.19. To obtain guidelines for preparing high-quality materials, the magnetic spectra of monodomain ferrite samples are studied via a numerical fitting method. According to the results of this permeability spectra fitting, the magnetic spectra of our prepared samples are mainly determined by the static spin susceptibility K s, spin resonance frequency ω 0, and relaxation frequency ω r. Specifically, we find that ω r varies with the frequency of the external field f. Furthermore, we demonstrate that Co2O3 influences the relationship between ω r and the frequency of the external field. According to theoretical expectations, a higher Q factor at frequency of 13.56 MHz could be obtained by using an appropriate Co2O3 content.

Silver end termination paste preparation for chip inductor applications

A silver end termination paste fired at low temperature (600–650 °C) for chip inductor applications is developed in this work. The lead-free glass chemical composition and glass content in the silver paste effects on the densification, microstructure and interfacial reaction between the end termination and NiCuZn ferrites were investigated using scanning electron microscopy, electron probe microanalysis, X-ray diffractometer and dilatometer. The results show that nearly complete densification can be obtained for the paste added with 40 wt% B2O3 glass. Optimal glass Bi2O3 content (about 6.5 wt%) and glass content (about 15 wt%) are helpful in promoting adhesion strength due to interfacial reaction enhancement between the glass in the paste and NiCuZn ferrites.

Structural and Magnetic Properties of Cr-Substituted NiCuZn Ferrite

Abstract Cr-substituted Ni0.2Cu0.2Zn0.6Fe2–x Cr x O4 ferrites (where x = 0–1.0) were prepared by solid-state reaction. The effects of Cr content on structural and magnetic properties were investigated. X-ray diffraction (XRD) revealed the formation of ferrite particles with cubic spinel structure. The lattice parameter and average crystallite sizes are much dependent on the chromium content and are found to decrease with its increasing. The initial permeability (μ i) and saturation flux density (B s) decrease with the increasing Cr content. In addition, without substituted ceramic samples possess lower quality factor (Q factor) than the NiCuZn ferrites with Cr substituted.

Effects of microstructure and CaO addition on the magnetic and mechanical properties of NiCuZn ferrites

In this study, the effects of grain size and the addition of CaCO3 on the magnetic and mechanical properties of Ni0.5Cu0.3Zn0.2Fe2O4 ceramics were investigated. The bending strength of the ferrites increased from 66 to 84MPa as the grain size of the sintered ceramics decreased from 10.25μm to 7.53μm, while the change in hardness was insignificant. The addition of various amounts of CaCO3 densified the Ni0.5Cu0.3Zn0.2Fe2O4 ceramics at 1075°C. In the pure Ni0.5Cu0.3Zn0.2Fe2O4 ceramic, second phase CuO was segregated at the grain boundaries. With the CaCO3 content ≥1.5wt%, a small amount of discrete plate-like second phase Fe2CaO4 was observed, together with the disappearance of the second phase CuO. The grain size of the Ni0.5Cu0.3Zn0.2Fe2O4 ceramic dropped from 7.80μm to 4.68μm, and the grain size distribution widened as the CaCO3 content increased from 0 to 5wt%. Initially rising to 807 after CaCO3 addition up to 2.0wt%, due to a reduced grain size, the Vickers hardness began to drop as the CaCO3 content increased. The bending strength grew linearly with the CaCO3 content and reached twice the value for the Ni0.5Cu0.3Zn0.2Fe2O4 ceramic with an addition of 5.0wt% CaCO3. The initial permeability of the Ni0.5Cu0.3Zn0.2Fe2O4 ceramic decreased substantially from 402 to 103 as the addition of CaCO3 in ferrite increased from 0 to 5wt%, and the quality factor of the Ni0.5Cu0.3Zn0.2Fe2O4 ceramic was maximized at 95 for 1.0wt% CaCO3 addition.

Sintering, microstructure and magnetic properties of low temperature co-fired NiCuZn ferrites with Nb2O5 and MoO3 additions

Sintering behavior and magnetic properties of NiCuZn ferrites with different amount of Nb2O5 and MoO3 additions were investigated. It was found that Nb2O5 and MoO3 additives could improve densification and promote uniform grain growth. The appropriate Nb2O5 and MoO3 additions not only efficiently increase the initial permeability (μi) and saturation flux density (Bs), but also noticeably reduce the remanent flux density (Br) and coercive filed strength (Hc) of the NiCuZn ferrites sintered at 925°C. By contrast, the NiCuZn ferrites with 0.2wt% Nb2O5 and 0.3wt% MoO3 additions showed excellent magnetic properties: μi=1097.88 at 100kHz, Bs=160.81mT, Br=63.55mT and Hc=26.6A·m-1.

Effect of Sintering Temperature on Magnetic Core-Loss Properties of a NiCuZn Ferrite for High-Frequency Power Converters

In an effort to find a magnetic material for making low-loss magnetic components for high-power-density converters, we investigated the magnetic core-loss characteristics of a commercial NiCuZn ferrite (LSF 50) at 5 MHz as a function of the sintering temperature of the ferrite powder. The ferrite powder was compacted into toroid cores and then sintered at 850°C, 900°C, 950°C, 1000°C, and 1050°C for 2 h. The sintered densities of the cores increased at higher sintering temperatures. The magnetic properties of the sintered cores—complex permeability and core-loss density—were measured. We found that both the real and imaginary parts of the relative permeability increased with sintering temperature. The core-loss results at 5 MHz showed that the cores sintered at 950°C and 1000°C had the lowest core-loss densities, being two to three times lower than that of a commercial NiZn ferrite (4F1) core. Microstructures of the sintered cores were examined by scanning electron microscopy; the grains grew significantly at higher sintering temperatures.

Structural Observations, Density and Porosity Studies of Cu Substituted Ni-Zn Ferrite through Standard Ceramic Technique

Polycrystalline NiCuZn ferrites prepared by solid state reaction method with various concentrations of copper generalized as Ni0.7-xCuxZn0.3Fe2O4 with the x varying from 0 to 0.50 in steps of 0.05 variations. In this paper we present the structural, density and porosity. The powders of the samples were used to characterize the x-ray diffraction. The XRD patterns of the samples provide the evidence of the single cubic crystal symmetry phase. The microstructure of the NiCuZn ferrite average grain size is recorded by SEM. The NiCuZn ferrite system having low cost and low firing metals for preparing the multi layer ferrite chip inductors and higher densification than the Mn-Zn ferrite.

Effects of Fe-deficiency on magnetic properties and Brillouin function characteristics for NiCuZn ferrites

The polycrystalline Ni0.56Cu0.10Zn0.34Fe2−xO4−3/2x (x=0.00~0.14) ferrites have been prepared by conventional oxide ceramics process. The effects of Fe-deficiency content on magnetic properties and Brillouin function characteristics for NiCuZn ferrites have been investigated in details. With the increase of Fe-deficiency content, the opposite variation trend are observed for the saturation magntic induction Bs and the coercivity Hc. More importantly, based on the Néel molecular field theory, for the spinel ferrites which do not only contain Fe3+ but also some other multiple magnetic ions (Ni2+ and Cu2+), the molecular field coefficients ωaa, ωbb and ωab=ωba are calculated by non-linear fitting method, and the Curie temperature Tc formula has been modified. With the increase of Fe-deficiency content, the values of ωaa and ωbb increase gradually, however, the value of ωab=ωba has a contrary trend which results in the decrease of the Curie temperature. In addition, the fitting Curie temperatures values are coincided well with the Curie temperatures calculated by the modified formula.