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The densified MnZn ferrite ceramics were prepared using the cold sintering process under pressure, with an acetate ethanol solution used as the transient solvent. The effects of the transient solvent, the pressure and annealing temperature on the density, and the micromorphology and magnetic properties of the sintered MnZn ferrites were studied. The densified MnZn ferrite was obtained using the cold sintering process and its relative density reached up to 85.4%. The transient solvent and high pressure are essential to the cold sintering process for MnZn ferrite. The annealing treatment is indispensable in obtaining the sample with the higher density. The relative density was further increased to 97.2% for the sample annealed at 950 °C for 6 h. The increase in the annealing temperature reduces the power loss at high frequencies. [ABSTRACT FROM AUTHOR]

In this study, MnZn ferrites with added YIG nanoparticles were developed for MHz frequency applications. The effect of the magnetic YIG additive on the power loss, initial permeability, and cutoff frequency of MnZn ferrites was investigated. A small quantity of added YIG effectively reduces the power loss and concurrently increases the initial permeability. Compared to the results for the MnZn ferrite with no added YIG, the optimal MnZn ferrite with 600 ppm added YIG exhibits a reduction in the power loss at 25°C of 56.4% and 36.6% at 1 MHz/50 mT and 3 MHz/10 mT, respectively, and a 13.9% increase in the initial permeability. This sample also exhibits a good stability of the power loss against temperature. The power loss remains below 205 kW/m3 over temperatures ranging from 25 to 140°C. The effect mechanism of YIG addition on the magnetic properties of MnZn ferrites was studied. An analysis based on the equivalent circuit model showed that the reduction in the eddy current loss and power loss mainly results from the increase in the grain boundary resistance caused by the addition of highly resistive YIG. [ABSTRACT FROM AUTHOR]

Hcp-Co-SiO 2 films with different thicknesses were fabricated by homogeneously distributing nanocrystalline Co particles with a size of 5∼10 nm in the amorphous SiO 2 matrix. The Co columnar crystals grow perpendicularly to the film and exhibit perpendicular magnetic anisotropy. The tilting angle (θ) of the magnetic moments to the vertical direction decreases to 7.5° as the film thickness increases to 1097 nm. The Co fraction reaches 0.64, leading to low coercivity of 30-35 Oe for magnetic indirect exchange coupling of closely packed Co nanocrystalline particles. Perpendicular anisotropy leads to a ripple-stripe domain with two orders of magnitude wider than the nanoparticle size. The natural resonance frequency of film is about 2.01 GHz, corresponding to low-anisotropy field. However, it increases to 18 GHz as in-plane magnetic bias field reaches 2400 Oe, exhibiting in-plane isotropy. This hcp-Co-SiO 2 nanocrystalline film provides an opportunity for potential application of isotropic films in micro-inductance and electromagnetic devices. • Hcp-Co-SiO 2 films were fabricated by homogeneously distributing nanocrystalline Co particles with in SiO 2 matrix. • The Co fraction reaches 0.64, leading to low coercivity of 30-35 Oe for magnetic indirect exchange coupling. • The Co columnar crystals grow perpendicularly to the film and exhibit perpendicular magnetic anisotropy. • The f r increases to 18 GHz as in-plane magnetic bias field reaches 2400 Oe, exhibiting in-plane isotropy. [ABSTRACT FROM AUTHOR]

A novel amorphous soft magnetic composites (ASMCs) for hundreds MHz frequency applications have been prepared under the hot-pressing molding by ultrafine submicron FeBP amorphous powders. These ultrafine submicron FeBP amorphous particles were synthesized with the NaBH 4 chemical reduction method and the particles size was regulated by the drop rate of the reducing agent. The morphology, microstructure, elemental composition and high-frequency magnetic properties of the amorphous soft magnetic composites was systematically investigated. The particle sizes of FeBP amorphous powders are distributed in 600–900 nm which gradually increase with the decrease of the drop rate of the NaBH 4 aqueous solution. Meanwhile, the Fe element content and saturation magnetization strength of the amorphous powder increase and the coercivity gradually decreases. The corresponded ASMCs also appear a commensurate permeability in the range of 6–9 responding to the GHz high frequency range with the lowest loss tangent only 0.20 and 0.44 at 500 MHZ and 1 GHz, respectively. Such ultrafine amorphous soft magnetic composites have enormous potential for high frequency applications in wide band gap semiconductor switching power supplies, RF inductors and chips. • The spherical amorphous powder was prepared by chemical reduction method with outstanding magnetic properties. • The particle size of the amorphous powder was regulated by adjusting the drop rate of the reducing agent solution. • The relationship between the powder particle size and the magnetic and electrical properties of ASMCs was elucidated. [ABSTRACT FROM AUTHOR]

In this work, the low-power-loss Mn–Zn ferrite was prepared by the traditional ceramic sintering process. This sample shows the good wide-temperature stability of power loss (P cv). In the whole measurement temperature range of 25 - 120 °C, P cv s maintain less than 100, 682, and 1455 kW/m3 at 100 kHz/100 mT, 500 kHz/100 mT and 800 kHz/100 mT, respectively. The effect of uniaxial compressive stress on power loss at 100, 500 and 800 kHz was investigated. Stress has greater impact on P cv at high frequencies and P cv increases remarkably. To clarify the mechanism of stress on power loss, P cv was divided into three parts including hysteresis loss (P hv), eddy current loss (P ev) and residual loss (P rv), and the effect of stress on each part of loss was discussed. At the low frequency of 100 kHz, P cv is mainly contributed by P hv. The applied stress leads the local anisotropic stress and makes domain wall displacement more difficult, which is the reason of the increase of P hv. When frequency increases to 500 and 800 kHz, P ev and P rv become more important. The compressive stress is in favour of electron transfer between Fe3+ and Fe2+ in grains and electron tunnelling effect at grain boundaries, which leads to the decrease of resistivity. This is the origin of enhanced P ev under the compressive stress. The enhanced P rv is related to the enhanced electronic diffusion under the compressive stress. The clarification of the mechanism of stress on power loss is beneficial to develop new soft ferrite materials with low stress sensitivity for high-frequency applications. [ABSTRACT FROM AUTHOR]

• A low temperature sintering process with the aid of sintering additive was developed to prepare fine-grain Mn-Zn ferrites. • Mn-Zn ferrite with low power loss and good wide-temperature stability was successfully prepared for the MHz application. • The effect of LiBO 2 sintering aid on magnetic properties of Mn-Zn ferrites was discussed. 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 LiBO 2 sintering aid was added to promote the low temperature sintering and densification. The effects of LiBO 2 on micromorphology and magnetic properties of the sintered Mn-Zn ferrites were investigated. With the aid of LiBO 2 , sintering temperature could be reduced as low as 990 °C. The optimum sample was obtained by the addition of 500 ppm LiBO 2 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 LiBO 2 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. [ABSTRACT FROM AUTHOR]

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. Co 3 O 4 was added and its content was optimized to achieve the broad-temperature characteristics of power loss. The optimal Co 3 O 4 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 Co 3 O 4 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 Co 3 O 4 reduces the residual loss and increases the cut-off frequency. This is ascribed to the induced uniaxial anisotropy of Co2+. [ABSTRACT FROM AUTHOR]

• The new Mn ferrite with low power loss at high frequencies of 1–3 MHz over a wide temperature range of 25–140 °C was successfully developed. • Power loss was divided into hysteresis loss (P hv), eddy current loss (P ev) and residual loss (P rv), and the effect of Ta 2 O 5 on each part of power loss at high frequencies was investigated. • Small content of Ta 2 O 5 segregates at grain boundaries and reduces P hv , P ev and P rv. • The mechanism of reduction of P hv , P ev and P rv by the Ta 2 O 5 addition was clarified. Dramatic increase of power loss in the MHz frequency range is the bottleneck problem for MnZn ferrites to be applied in high-frequency power electronic devices. In this work, manganese ferrites with low power loss in the frequency range of 1–3 MHz have been developed by the addition of Ta 2 O 5. The manganese ferrite with 300 ppm Ta 2 O 5 exhibits excellent P cv performance. P cv at 25 °C is as low as 41, 94 and 164 kW/m3 under measurement conditions of 1 MHz/50 mT, 2 MHz/50 mT and 3 MHz/30 mT, respectively. Excellent temperature stability of power loss in the temperature range of 25–140 °C is also achieved in this sample. Power loss was divided to three parts of hysteresis loss, eddy current loss and residual loss. Ta 2 O 5 segregates at grain boundaries and reduces all three parts of loss. The mechanism of Ta 2 O 5 influence on each part of loss has been clarified. [ABSTRACT FROM AUTHOR]