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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]

Phase composition, microstructure and magnetic properties of the low-temperature-fired NiCuZn ferrites doped with different concentrations of Bi2O3 were investigated. A proper content of Bi2O3 doping could trigger the formation of a dual microstructure of the ferrites. The before and after 'critical' doping content, i.e. low- and high-Bi2O3-doping modes,enabled the ferrites to obtain sufficiently high density and equal permeability. The former sample obtained a uniform, dense and fine-grain-sized microstructure, which was beneficial to improve the high-frequency characteristic and Q-factor characteristic of the low-temperature-fired NiCuZn ferrite; moreover, the saturation flux density was higher. However, the latter sample obtained a uniform, dense and large-grain-sized microstructure with more grain-boundary-dopant, which was beneficial to improve the DC-bias superposition characteristic of the ferrite. These comparative results can essentially guide the engineering applications of the low-temperature-fired NiCuZn ferrites. [ABSTRACT FROM AUTHOR]

Mn-Zn ferrites with high initial permeability ( μ ) and high saturation magnetic flux density ( B ) were successfully synthesized by using a conventional ceramic processing route with addition of MoO. The structure, morphology, magnetic properties, and complex impedance of all samples were investigated by X-ray diffraction, scanning electron microscopy, DC magnetic instrument, and precision LCR meter. The addition of MoO promotes the growth of larger and more uniform grains and therefore enhances the μ . Meanwhile, it improves the density and hence the B . Through the analysis of complex impedance spectra by an equivalent circuit model, it is demonstrated that MoO mainly exists at grain boundaries and improves the impedance in a wide frequency range. [ABSTRACT FROM AUTHOR]

M-type strontium hexaferrites with the chemical composition of SrLaCaFeCoO were prepared by ceramic process. X-ray diffraction, X-ray photoelectron spectrometer, scanning electron microscopy, vibrating sample magnetometer and permanent magnetic measuring system were employed to investigate the influence of La-Ca-Co substitution on the microstructure and intrinsic coercivity of the powder and sintered samples. The results show that both Sr-ferrite powders and sintered samples with Ca-La-Co substitution have high intrinsic coercive forces more than 500 KA/m. The acting mechanism of La-Ca-Co substitution on the high coercivity and microstructure was discussed. La-Co substitution causes not only the increase of the anisotropy, but also the decrease of the grain size, which increases the coercivity greatly. The presence of Ca together with La and Co in the substituted system helps to increase the magneto-crystalline anisotropy field. However, it accelerates the sintering and the grain growth, making the intrinsic coercivity of the sintered magnets decrease. [ABSTRACT FROM AUTHOR]

To meet the challenge of varied working temperatures of inductance components in new energy vehicle and 5G communication, the high- T C high-permeability MnZn ferrite with excellent temperature stability was developed by the addition of SnO 2. In this series of samples, initial permeability μ i maintains large values in a wide temperature range. With increasing the SnO 2 content, the temperature of the second permeability peak T sp decreases and meanwhile Curie temperature T C maintains as high as 160 °C. For the best sample with 6000 ppm SnO 2 , μ i at 25 °C is 7244 and exhibits the excellent temperature stability with the low specific temperature coefficient of 0.35 × 10−6 °C−1 between 25 and 130 °C. The addition of SnO 2 generates Fe2+ and adjusts the magneto-crystalline anisotropy constant K 1 = 0 point, which is responsible for the wide-temperature high permeability. The effect of SnO 2 addition on magnetization process has also been clarified. [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]

Low-temperature-fired NiCuZn ferrites with Al 2 O 3 (0–2 wt%) addition were prepared via the conventional solid-state reaction. The effects of different Al 2 O 3 doping contents on phase composition, microstructure and magnetic properties, especially DC-bias-superposition characteristic, were investigated. Results indicated that the addition of an appropriate amount of Al 2 O 3 content to NiCuZn ferrites could increase coercivity and the thickness of the nonmagnetic grain boundaries, thereby increasing the demagnetising field and subsequently reducing the decrease rate of the magnetic permeability under superposition magnetic fields. Simultaneously, permeability and saturation flux density monotonously decreased with the increase in Al 2 O 3 doping content. With the addition of 1.5 wt% Al 2 O 3 , the sample obtained relatively high permeability (∼70.7) and perfect DC-bias-superposition characteristic (H 70% –840 A/m). This ferrite material has favourable application prospects for recognising chip inductors that can carry large currents. • Al 2 O 3 addition was mainly deposited at the grain boundaries. • Al 2 O 3 led to the increase of Hc and DC-bias-superposition characteristic. • Al 2 O 3 led to the decrease of density and permeability. • 1.5 wt% Al 2 O 3 added ferrites achieved permeability of ∼70.7 and H 70% –840A/m. [ABSTRACT FROM AUTHOR]

Although there is a tradeoff between high B s and low core loss for MnZn power ferrite, in the current work, high B s and a low core loss ( P cv ) were achieved simultaneously by increasing the content of Fe 2 O 3 and by adjusting the partial pressure of oxygen ( P O 2 ) during sintering process, respectively. Additionally, the influence of P O 2 on the P cv was also investigated. The MnZn ferrite cores were prepared by conventional ceramic process. With increase in P O 2 from 0.35% to 1.90%, the bottom temperature of P cv ( T ) curve shifted to a higher temperature, and simultaneously the minimum P cv at the bottom temperature decreased continuously. P cv in a low frequency range was divided into the hysteresis loss ( P hv ) and eddy current loss ( P ev ). Both P hv and P ev decreased with increasing P O 2 . At high P O 2 cation vacancy was generated, which facilitated the transport of dopant, such as Ca and Si to the grain boundary region. This induced high resistance at the grain boundary which in turn reduced the P ev . Meanwhile, the transport of dopants from intragranular to grain boundary also reduces the defects in grains, which helped to decrease the P hv , coercivity and remanence. [ABSTRACT FROM AUTHOR]

• Co-Ba composite ferrites (CBCF) insulation layer was successfully cladded on the surface of Fe powder by a simple method. • Clausius-Maxwell formula model was used to simulate permeability in Fe@Co-Ba composite ferrites theoretically. • The SMCs coated with CBCF maintains high permeability (up to 121) and low core loss (129 kW/m3 at 20 mT, 100kHz). • Evolution of the Co-Ba composite ferrites coating with the annealing temperature is observed by BSEM images. To balance the core loss and permeability of soft magnetic composites (SMCs), a Co-Ba composite ferrite insulation layer was employed to clad the surface of reduced iron powder by sol-gel method. The successful preparation of the honeycomb-like Co-Ba composite ferrite coating layer was verified by scanning electron microscopy (SEM), the composition of the coating was determined by X-ray diffraction (XRD), and the magnetic properties were tested with a B-H curve analyzer. BSEM images of the polished cross-section and core loss separation results confirmed that an excessively high annealing temperature causes the composite ferrite insulation layer to fail. A high effective permeability of up to 121 at 300 kHz and low core loss (P cv) of 129 kW/m3 at 100 kHz and 0.02 T were obtained in prepared samples at the optimized annealing temperature of 500 °C. Subsequently, simulation analysis based on the Clausius-Maxwell formula model was used to confirm the feasibility of the enhancement on effective permeability in Fe@Co-Ba composite ferrite theoretically. The agreement between simulation and experimental results further indicated that a good balance between the core loss and permeability of Fe-based SMCs was achieved by Co-Ba composite ferrite cladding. [ABSTRACT FROM AUTHOR]

• The quick heating rate in thermal debinding resulted in the CuO precipitate. • The CuO precipitation was associated with the small amounts of remaining binders. • The quick heating rate in themal debinding resulted in the intergranular fracture. • The slow debinding (0.6 °C/min) improved bending strength and magnetic properties. NiCuZn ferrite ceramics were prepared by injection molding, debinding and sintering at 1150 °C. The effects of heating rate in thermal debinding on microstructure, bending strength and magnetic properties of sintered samples were investigated by scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, the Dual Column Tabletop Testing Machine, RF impedance Analyzer and B-H curve analyzer. The results showed the heating rate in thermal debinding played an important role on the sintered NiCuZn ferrite prepared by injection molding. When the heating rate in thermal debinding was quick above 1.2 °C/min in the lager cuboid samples, CuO precipitate was found at the grain boundary of ferrite and the intergranular fracture occurred, which was different from the normal transgranular fracture under the condition of slow heating rate. Furthermore, the density, bending strength, permeability and core loss of the sintered samples were improved with the decrease of heating rate. The influencing mechanism of thermal debinding on the difference was also discussed. [ABSTRACT FROM AUTHOR]

Fe@Composite-Ferrite soft magnetic composites (SMCs) were successfully fabricated by ions doping on the surface of Fe@Fe 3 O 4 powders which can improve the thermal stability and insulation. Compared with the traditional SMCs which were constructed by soft magnetic particle and non-magnetic boundary, this new material maintains high B m of 1.3214 T at 5000 A/m, 50 Hz, high μ max of 625.14 and low P cm of 10.02 W/kg at 50 Hz, 1.3 T. A three-dimensional simulation loss model and correlation theory of magnetic domain walls were used to analyze the relative loss mechanism and the effect of the new ferrite coating on the domain walls during magnetization. The novel composite-ferrite boundary greatly reduces the pinning, promoting domain wall motion and increasing the number of active magnetic objects. • Composite ferrite coating can be formed on the surface of iron powders by a simple and controllable method. • Comparing with the traditional SMCs, the Fe@Composite-Ferrite SMCs maintains higher magnetic induction, better magnetic permeability and lower total core loss. • The effects of heat treatment temperature and the particle size of iron powder on magnetic properties have been studied. • A three-dimensional simulation loss model and correlation theory of magnetic domain walls were used to analyze the relative loss mechanism. [ABSTRACT FROM AUTHOR]