Low temperature sintered MnZn ferrites for power applications at the frequency of 1 MHz

The low power loss Mn-Zn ferrites with fine grains were developed by the low-temperature-sintering ceramic process for power applications at a high frequency of 1 MHz. The LiBO₂ sintering aid was added to promote the low temperature sintering and densification. The effects of LiBO₂ on micromorphology and magnetic properties of the sintered Mn-Zn ferrites were investigated. With the aid of LiBO₂, sintering temperature could be reduced as low as 990 °C. The optimum sample was obtained by the addition of 500 ppm LiBO₂ sintered at 1020 °C. The average grain size of this sample is 2.78 μm, the density reaches 4.82 g/cm³, and the minimum power loss is 310 kW/m³ at 1 MHz/30 m T and 25 °C. This sample shows good wide-temperature stability of power loss. The mechanism of power loss affected by the LiBO₂ addition was also discussed. The ceramic sintering process combining the low temperature sintering and the sintering aid offers a new way to develop high-frequency Mn-Zn ferrites.     

Correlating the microstructure with magnetic properties of Ti-doped high-frequency MnZn ferrite

In this study, high-frequency MnZn ferrites are prepared for power applications at 10 MHz using solid-state reaction method. The sample doped with 3000 ppm TiO₂ yields the optimal comprehensive magnetic properties, with an initial permeability of 792, power loss of 415 kW/m³ (10 MHz, 5 mT, 25 ℃), and saturation induction of 460 mT. This indicates significant progress compared to previously reported results. The mechanisms of property optimisation, microstructure and domain structure evolution also discussed with TiO₂ doping. The precipitation of Ti at the grain boundary can promote a high-density microstructure and favour the formation of magnetic monodomain in MnZn ferrites. Our results elucidate the correlations between microstructure, domain structure, and high-frequency performance, and present a potential roadmap for the development of high-frequency soft magnetic ferrites.     

低损耗MnZn铁氧体材料的研究现状及发展趋势

介绍了低损耗MnZn铁氧体的研究现状及TDK,SIMENS等公司最新产品情况,通过对原材料的性质、掺杂和烧结工艺分析,说明它们决定了低损耗MnZn铁氧体的微观结构,同时也表明原材料的匹配对提高材料的性能有重要作用.探讨了低损耗MnZn铁氧体材料的工艺发展方向.     

Microstructural and magnetic evolution of MnZn/FeSiAl composites synthesized by mechanochemistry

Spinel MnZn ferrites (MZFs) were synthesized by solid-state reaction via mechanochemical method. Microwave absorbing composites were fabricated with MZFs and FeSiAl powders. Microstructural evolutions and the influence of MZFs content on magnetic properties, shielding efficiency and reflection loss of composites were investigated. Sintering at 1200 °C, spinel MZFs can be synthesized. With increasing MZFs content, saturation magnetization decreased from 106.94 to 89.71 emu/g. For shielding efficiency and reflection loss, the optimal MZFs content is 10 wt%, the total shielding efficiency reaches to 45 dB. The bandwidth of reflection loss which exceeding −10dB reaches to 4.6 GHz. With increasing it to 15 wt%, the minimum reflection loss can reach to −16.5 dB, but the bandwidth narrowed. The attenuation coefficient decreased with increasing MZFs content.     

Two-step doping of SiO2 and CaO for high-frequency MnZn power ferrites

SiO₂ and CaO are empirical but effective co-doping oxides for low-loss MnZn soft ferrites. However, the underlying mechanism of the synergistic effect remains unclear. Herein, we systematically investigate the effect of SiO₂ and CaO, and propose a two-step doping strategy for high-frequency MnZn ferrites. It is found that SiO₂ facilitates the formation of mono-domain grains, thereby reducing the residual loss at high frequency. Meantime, CaO may dissolve into ferrite matrix with improved resistivity but abnormal growth of grains. By preliminarily coating MnZn particles with SiO₂, the reaction between CaO and ferrite matrix could be effectively suppressed, leading to the formation of continuous calcium silicate grain boundary (GB) phase. Consequently, superior high-frequency performance than traditional one-step doping strategy including initial permeability of 498, cut-off frequency of 12.6 MHz, power loss of 326 kW/m³ (5 MHz, 10 mT) can be obtained, which is desired by miniaturized electronic devices.     

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.     

Development of Mn-Zn power ferrite with low losses over a broad temperature range for applications in the high frequency region of 0.5-3 MHz

Due to the rapid development of electronic devices towards high frequency, miniaturization, and high efficiency, it is imperative to develop MHz-frequency power ferrites exhibiting low loss over a broad temperature range. In this work, the broad-temperature low-loss Mn-Zn power ferrites operating in the frequency range of 0.5-3 MHz have been fabricated following the traditional oxide ceramic process. Co₃O₄ was added and its content was optimized to achieve the broad-temperature characteristics of power loss. The optimal Co₃O₄ content was determined to be 0.35 wt%. The power losses of this material are less than 30, 120, and 30 kW/m³ in the broad temperature range from 0 to 120 °C under the conditions of 500kHz/50 mT, 1MHz/50 mT, and 3MHz/10 mT, respectively. This material is an ideal material for applications in power conversion electronics at high frequencies (0.5-3 MHz). The effect of Co₃O₄ addition on power loss is discussed based on the compensation model of magnetocrystalline anisotropy constant. Analysis of the three parts of power loss reveals that the residual loss gradually becomes to be predominant above 1.2 MHz. The addition of Co₃O₄ reduces the residual loss and increases the cut-off frequency. This is ascribed to the induced uniaxial anisotropy of Co²⁺.     

Enhanced gyromagnetic properties of Cu-substituted LiZnTi ferrites for LTCC applications

In this work, we prepared a type of LiZnTiCu ferrite with a large grain size and enhanced magnetic properties at ～900 °C by substituting Cu²⁺ ions and doping LBSCA glass. Rietveld refinement of XRD patterns indicates that the Fe³⁺ ions in B sites are partially replaced by the Cu²⁺ ions, which causes the monotone increase of lattice constant. SEM results show that the interaction of CuO nanoparticles and LBSCA glass causes two changes in the grain growth of the LiZnTiCu ferrites. The grain growth is suppressed when the amount of CuO nanoparticles is less than a threshold value (x = 0.05 for 900 °C; x = 0.20 for 875 °C). However, when enough CuO nanoparticles are added, the ferrites possess a large and compact microstructure. The variation of magnetic hysteresis (M-H) loops confirms that M_s follows the Néel's collinear spinel model with the increasing number of CuO nanoparticles (x ≤ 0.25). Finally, a type of LiZnTiCu ferrite (x = 0.15) with uniform large grains (average size >10 μm) and good magnetic parameters (4πM_s = 3457.59 G, H_c = 224.4 A/m and B_s = 236.4 mT) is obtained at ～900 °C.     

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.     

Effect of particle size of as-milled powders on microstructural and magnetic properties of Y3MnxAl0.8-xFe4.2O12 ferrites

Yttrium iron garnet ferrite using the chosen stoichiometry of (Y₃)(Mn_xAl_0.8-xFe_4.2)O₁₂ with x = 0.1 and different milling powder sizes were prepared through ball milling for various milling times to study the effect of powder size reduction on the resulting microstructural and magnetic properties. Sintered yttrium iron garnet ferrites were characterized by X-ray diffraction analysis and scanning electron microscopy. The particle size (D₅₀) of as-milled calcined powder was decreased using ball milling (from 3.682 μm for a 0.5-hour-long milling to 1.606 μm for a 2.5-hour-long milling). Scanning electron microscopy analyses confirmed that the sintered grain exhibited a crystal size that was increased from initial values (average crystal grain sizes of 3.5 ± 0.1 μm for 0.5 hour of milling) up to 6.2 ± 0.1 μm after 2.5 hour of ball milling and the subsequent sintering process. The same sintered specimen after 2.5 hour of ball milling exhibited an obvious increase in saturation magnetization (4πM_s), remanence (B_r), and squareness ratio (namely B_r/4πM_s); it also caused a notable decline in coercivity (H_c) and ferromagnetic resonance line width (∆H), which were attributed to the introduction of a smaller size of calcined powder after milling and subsequently resulted in a larger sintered grain. Furthermore, a sufficient spin-wave line width (∆H_k) and low insertion loss (|S₂₁|) were obtained for the operation of the microwave device. The aforementioned results are all beneficial to the use of yttrium iron garnet ferrite in microwave applications. A correlation between the calcined powder size after milling, grain crystal size after sintering, and magnetic properties was evident in this study. The strict control of calcined powder size after milling is critical in tailoring suitable magnetic properties for yttrium iron garnet ferrite manufacturing processes.     

Influence of doping on magnetic and electromagnetic properties of spinel ferrites

In this study, spinel Ni_0.5Zn_0.5Fe₂O₄ doped with transition metal ions as well as rare-earth ions Ni_0.4Zn_0.4M′_0.2Fe₂O₄ (M′ = Cu, Dy, Gd and Lu) and M″_0.5Zn_0.5Fe₂O₄ (M″ = Ni, Mn and Co) are developed using the sol-gel auto-combustion route, and the role of substitution on electromagnetic properties is investigated. The powder X-ray diffraction accompanied by Rietveld refinement signifies a single-phase spinel ferrite that belongs to Fd-3m space group for all the compositions. Rietveld refinement confirms that doped Cu²⁺, Dy³⁺, Gd³⁺ and Lu³⁺ ions are at random distribution between spinel tetrahedral and spinel octahedral sites against their preferential occupancy. The saturation magnetisation (M_S) of Ni_0.5Zn_0.5Fe₂O₄ (M_S = 50.5 emu/g) increased with partial doping showing M_S = 60.08 emu/g for transition-metal doped Ni_0.4Zn_0.4Cu_0.2Fe₂O₄ and M_S = 109.7 emu/g for rare-earth doped Ni_0.4Zn_0.4Dy_0.2Fe₂O₄, which was the highest among all the doped compositions. Doping enhances the dielectric permittivity of Ni_0.5Zn_0.5Fe₂O₄ from 4.2 to 6.5 for Ni_0.4Zn_0.4Cu_0.2Fe₂O₄ and 7.7 for Ni_0.4Zn_0.4Dy_0.2Fe₂O₄. Further, the reflection coefficient (R_L) of all the doped compositions of Ni_0.4Zn_0.4M′_0.2Fe₂O₄ (M′ = Cu, Dy, Gd and Lu) was less than −8 dB (85% absorption) throughout the frequency band of 8–12 GHz with an optimum material thickness of 3.5 mm. Transition metal ion doped Ni_0.4Zn_0.4Cu_0.2Fe₂O₄ resulted in further improvement of its absorption characteristics of the incident EM waves with reflection coefficient (R_L) less than −10 dB (between 84.15% and 90%) between 10 and 12 GHz at a material thickness of 3.5 mm in the X-band frequency range.     

ZrO2和SnO2复合掺杂对贫铁配方的MnZn铁氧体磁性能和电性能的影响

通过ZrO2与SnO2复合掺杂制备了低损耗的MnZn铁氧体材料.研究了在贫铁配方的基础上添加SnO2-ZrO2对MnZn铁氧体微观结构、电性能以及磁性能的影响.结果表明,适量的SnO2-ZrO2复合掺杂有利于促进晶粒均匀致密,明显提高了材料的电阻率,降低比损耗因子,在ξ(SnO2:ZrO2)为3:1时材料的电阻率达到最大值29.5 Ωm,比损耗因子达到最小值4.8×10-6.复合掺杂还能提高材料的居里温度、饱和磁感应强度和起始磁导率,当ξ(SnO2:ZrO2)为3:1时磁性能都达到最佳.     

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 13.56 MHz 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 0.45 wt% Co₂O₃-doped ferrite (A_0.45) was similar to that of 0.10 wt% Co₂O₃-doped ferrite (B_0.10). 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.     

Enhancement in magnetic permeability of Ni-Co-Zn ferrites using CuO doping for RF and microwave devices

Novel soft magnetic ferrite materials will play a crucial role in next-generation trillion-dollar sensor technologies related to 5G communications and internet of things as these materials can achieve improved wireless power/signal transfer efficiency with high operation frequency. In this work, Ni_0.4Co_0.25Zn_0.35Fe₂O₄ ferrites with high permeability and low magnetic loss were prepared for RF and microwave device applications. Composition and microstructure control is crucial to obtain the desired magnetic and loss properties. CuO dopant (x = 0 wt% to 20 wt%) were employed during the synthesis of Ni_0.4Co_0.25Zn_0.35Fe₂O₄ ferrite specimens to modify the microstructures, thus improving the magnetic properties of the ferrites. High value of measured relative permeability (μ’ of 4-10) and relatively low magnetic loss tangent ( of 0.01-0.1) has been achieved at frequency range between 100 and 800 MHz. Addition of CuO, especially up to 3 wt%, can cause a significant increase in permeability. Real part of the permeability of 3.87 and 10.9 has been achieved for undoped and 3 wt% CuO doped specimens, while noticeable reduction in magnetic losses has been observed for the doped sample measured at 400 MHz. The resonance frequency of synthesized ferrites has also been shifted into GHz range, when higher concentration of CuO dopants (>5 wt%) were employed.     

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

NiCuZn ferrites doped with 0.5 wt% Bi₂O₃ and different Li₂CO₃ contents (0–0.25 wt%) 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 >0.2 wt%. Maximum magnetic flux density (431.1 mT at room temperature, 339.6 mT at 100 °C) and minimum power loss were achieved at 0.2 wt% Li₂CO₃. These findings suggested the suitability of 0.2 wt% Li₂CO₃ for applications in low-temperature co-fired ceramic magnetic power components and modules.     

Structural parameters,energy states and magnetic properties of the novel Se-doped NiFe2O4 ferrites as highly efficient electrocatalysts for HER

This study is devoted to NiFe₂O₄ with different masses of Se (NFO + x%Se) (x = 0.0–4.0%) spinel ferrite nanoparticles production and investigation. The results of the crystal structure, microstructure and magnetic properties are presented as a function of the chemical content of the NFO + x%Se. Superparamagnetic (at 300 K) and ferrimagnetic (at 10 K) states are observed for all samples in the wide magnetic field range. The field dependencies of the magnetization show that Se-substitution does not change the main magnetic characteristics when x<2.0%. We observe a non-linear dependence of magnetic parameters for sample with x ≥ 2.0% (for NFO+2%Se, we determine the increase of the main magnetic parameters for 20% of the average values and the minimum values belong to the NFO+3%Se). The undoped sample and NiFe₂O₄+x%Se are soft magnets and characterized by the low coercivity (varying in the range 560–647 Oe). At T = 10 K squareness ratio (Sq. = Mr/Ms) is in a range of (0.216–0.318). This indicates a preferable single-domain state of crystallites, which differs from the magnetic structure at T = 300 K. Furthermore, the NFO + x%Se (x = 2.0) have a low overpotential of about ?327 mV, and a small Tafel slope of 91 mV/dec, which makes it a better for HER (hydrogen evolution reaction) catalyst than the undoped NiFe₂O₄.     

单组分高周波固化木工胶的制备与性能研究

以改性VAE(醋酸乙烯-乙烯共聚物)乳液为木工胶的基体树脂、硼酸为增黏剂、异氰酸酯为交联剂和NaCl为抗冻剂等,成功制备出一种可高周波固化的单组分拼板胶。结果表明:当m(硼酸):m(聚乙烯醇)=0.4:10、w(交联剂)=5%和w(NaCl)=1.0%时,木工胶的综合性能较好,其压缩剪切强度超过欧洲DIN EN 204—2001标准;高周波固化木工胶(不必外加固化剂)的后期性能优于常规加压固化木工胶;该木工胶虽可作为某些中软质板材的拼板胶,但其对西南桦等硬木板材的粘接效果相对较差。     

Influence of the magnetic field on the alignment degree of the anisotropic strontium ferrites for elastomer bonded magnets

In this work, the influence of the magnetic field on the alignment degree of the magnetic particles and on the magnetic energy flux of elastomer bonded magnets are investigated. For the investigations, a strontium ferrite filled nitrile butadiene rubber is used. The change of magnetic flux density in the injection molding tool cavity was realized by changing the current at the rectifier. The alignment degree of the magnetic particles increases with increasing magnetic field in the injection molding tool cavity. Above a certain current strength, a saturation behavior of the alignment degree of the magnetic particles and the magnetic energy flux is reached. The change of the cavity magnetic field leads to an improvement of the pole angle error up to a current of 10 A. An increase of the current above 10 A leads to hardly any improvement of the pole angle error, since a saturation in the alignment of the magnetic particles has already been reached.     

Thermo-magnetic properties of Fe2O3-doped lithium zinc silicate glass-ceramics for magnetic applications

The crystallization behaviour and thermo-magnetic characteristics of glass-ceramic based on the 15Li₂O–20ZnO–10CaO–55SiO₂ system doped with varied Fe₂O₃ additions (0.0125, 0.025, and 0.05 mol) are described in this work. In some cases, Al₂O₃ was also added to the iron-containing sample. Glasses were successfully prepared by melt-quenching technique and converted into glass-ceramics by controlled heat-treatment, using DTA, SEM, XRD, and VSM techniques. The density, thermal expansion coefficients (TCE), and magnetic characteristics of the glass-ceramic were examined. XRD results confirmed characteristic peaks for various phases like quartz, Li₂ZnSiO₄, wollastonite, Li₂Si₂O₅, ZnFe₂O₄, and β-spodumene. By doping Fe₂O₃ and Al₂O₃ with lowering annealing temperature, the particle size was reduce, resulting in glass-ceramics with a more uniform and dense microstructure. The density of glass-ceramics rises from 2.74 g/cm³ to 3.45 g/cm³, whereas the TCE values in average 14–78 × 10⁻⁷/°C with temperature range of 25–500 °C. The doped glass-ceramics have superior magnetic properties with saturation magnetization (0.143–0.548 emu/g), the coercivity force (65.116–86.359 G), and remanence magnetization (0.074–0.436 emu/g). Under an alternating magnetic field, the presence of the Zn-ferrite phase in the glass-ceramics improves their magnetic properties and increases their heat-generating capability. Certain features of the doped glass-ceramics control the extensive variety of possibilities for their usage in various magnetic applications particularly for cancer hyperthermia treatment.