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High-temperature oxidation resistance of Nd–Fe–B magnetic powder is of great importance for its application in bonded magnet fields. In this work, the refinement and surface modification of Nd–Fe–B magnetic powders were integrated and achieved simultaneously. The effects of phosphoric acid, isopropyl tris-(dioctyl pyrophosphate acyloxy) titanate (ITDT), and the synergistic addition of them on the oxidation resistance of the powders were investigated. Also, the formation mechanism of the protective layer on the Nd–Fe–B powder surface has been proposed. The surface morphology, phase structure, oxidation resistance, and magnetic properties were studied. The results show that the synergistic surface modification exhibited optimal oxidation resistance on the refined magnetic powders. Furthermore, the obtained powders were bonded with polyphenylene sulfide to illustrate the effect of high-temperature oxidation resistance in practical application. The ITDT showed excellent protective performance for the magnetic properties at room temperature, whereas the phosphate showed an excellent oxidation resistance at high temperatures.

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.

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+.

Soft magnetic composites (SMC) with a bionic shell structure and a delicate, regular layered arrangement were prepared via a casting process. The permeability of composite samples was 140 at 5 MHz for plane anisotropy, while that of the spherical-particle-constructed material is only 14. According to classical loss separation results, the layered bulk material without an SiO2 coating exhibited lower hysteresis loss. In contrast, the layered bulk material coated with SiO2 showed lower eddy current loss, attributed to the increase in resistivity resulting from the SiO2 coating. The magnetic loss of the layered bulk materials was 588 kW/m3 at 50 mT and 100 kHz. SMC materials with this structure are anticipated to have strong potential for magnetic cores used in high-efficiency power supplies.

Fe-based soft magnetic composites (SMCs) co-coated with Bi2O3 and silane, used as the low melting point binder and the insulating layer, respectively, were successfully prepared. The SMCs show improved mechanical strength, thermal stability, and insulation compared to other soft magnetic composite materials. The obtained SMCs exhibit a high Bm of 1.2607 T at 5000 A/m, 50 Hz, a high μmax of 497, and a low Pcm of 81.8 W/kg at 50 kHz and 50 mT for a completely homogeneous thin insulating coating. In addition, the transverse rupture strength of such materials is up to 81.2 MPa, which is extremely important for high-speed motors. Furthermore, the permeability and magnetic loss are stable under stress. Nonlinear curve fitting was used to build the loss model and then separated into the hysteresis loss, the eddy current loss, and the excess loss. The loss mechanism of SMCs with different coatings and micro-stress was explored and verified via this model. When compared to traditional SMCs, this material coated with Bi2O3 and silane shows a lower loss and a higher transverse rupture strength. This research expands the application fields of iron-based SMCs, especially in practical applications of soft magnetic components in high-speed motors.

Replacement of samarium (Sm) with abundant yttrium (Y) can help solve the potential shortage of Sm in the preparation of promising Sm2Fe17Nx magnets. In this article, phase composition, microstructure and magnetic properties of (Sm1–yYy)2Fe17Nx (y = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were investigated. Maximum energy product (BH)max is improved when less than 40 at% Y is doped in (Sm1–yYy)2Fe17Nx powder. In particular, when 20 at% Y replaces Sm, (BH)max of (Sm1–yYy)2Fe17Nx powder increases by 15.1% from 131.7 to 151.6 kJ/m3. The effect of annealing temperature on the structural properties of high Y doping (Sm0.6Y0.4)2Fe17 and the magnetic properties of the corresponding nitrides were subsequently investigated. In the RE2Fe17 phase grain combination process, the interlaced structure of the rhombohedral Th2Zn17-type structural phase and the hexagonal Th2Ni17-type structural phase is formed. Due to short-range exchange coupling, the nitride with the highest content of two interlaced RE2Fe17 phases has the highest magnetic properties: Br = 1.23 T, HcJ = 443.9 kA/m and (BH)max = 197.6 kJ/m3.

In this work, we prepared the nanocrystalline near-equiatomic FePt thin films by electrodeposition and explored the effects of annealing temperature and annealing time on morphology, structure, and magnetic properties of FePt film. The fcc-FePt phase starts to form when annealing at 400 °C under the 15% H2 gas mixture. With increasing annealing temperature from 400 to 800 °C, the FePt film experiences a gradual phase transformation from the soft magnetic fcc phase to the permanent magnetic fct L10 phase. The transition degree of the L10 phase is achieved to be 0.94 and coercivity reaches a maximum of 1.5 T for the sample annealed at 800 °C for 4 h. A shoulder behavior in the M(H) curves is found in the electrodeposited FePt films. Through fitting the M(H) curves by the model based on the transition degree of the L10 FePt phase, the shoulder behavior is quantitatively confirmed to originate from the coexistence of the soft magnetic fcc phase and the permanent magnetic L10 phase. The magnetic exchange coupling between the soft magnetic and permanent magnetic nanocrystalline phases is negligible in the electrodeposited FePt films due to that the substrate Ag diffusion into the FePt film separates the FePt nanocrystalline phases.

In this report, we designed and fabricated carbon-coated honeycomb microwave absorbing materials (HMAMs), which were lightweight with high stiffness and exhibited broadband performance. The effect of structural parameters such as pore size, honeycomb height, coating thickness, permittivity and dielectric dissipation factor of the coating, on the microwave absorption was analyzed in detail. An effective homogeneous model was established through the effective medium theory, which was used to predict the microwave absorption properties and elucidate the mechanism. The fabricated HMAMs showed a broadband absorption property with three absorption peaks located at 4 GHz, 10 GHz and 17 GHz with reflection loss of −10 dB, −20 dB, −25 dB, respectively. This paper not only fabricates a multiple absorbing band HMAMs, but also provides an intuitive overview of the factors affecting absorption performance of HMAMs. Additionally, the proposed method is also capable of predicting microwave absorption properties of HMAMs.

In this paper, Injection molding, debinding and sintering of ZrO2 ceramic modified by silane coupling agent (A151) were studied by measuring the melt index of feedstocks, the soluble removal ratio of green parts, the bending strength of green and sintered parts, the surface and fractural morphologies of sintered parts. The results showed that the melt index of ZrO2 feedstocks, the weight removal ratio of soluble binders, and the bending strength of green parts increased after adding A151. When the density of sintered parts was between 5.97–6.03 g/cm3, it was not the main factor influencing the bending strength. However, the bending strengths of sintered parts decreased due to microcrack formation when thermal debinding process was too fast or slow. The interesting phenomenon of the abnormal grain growth with transgranular fracture in the sintered parts obviously occurred above 1550 ℃, which made the effect of sintering temperature on the strength become complex.

Sm2Fe17 prepared by reduction-diffusion method needs to be washed with water to remove calcium oxide. Electrochemical corrosion occurs when Sm2Fe17 powder is in contact with liquid water. Corrosion mechanism of H2O on Sm2Fe17 powder and nitrogenation process of corroded Sm2Fe17 were studied by analyzing the structure and morphology. It is indicated that the metallic hydroxide forms and deposits on the Sm2Fe17 powder surfaces during water corrosion. At the same time, oxygen and hydrogen enter the unit cell of Sm2Fe17, causing a slight increase in Curie temperature. In the subsequent nitriding process, the hydroxide is dehydrated and hydrogen is desorbed. The resulting oxide reacts with Sm2Fe17Nx to form α-Fe and Sm2O3. Thermodynamic calculations using the HSC Chemistry 6.0 software indicate that the reaction can occur spontaneously. The effect of water corrosion on the magnetic properties of the nitride can be eliminated by hydrogen reduction prior to nitriding.

The structural, heat capacity, and magnetic properties of Y2Mo2(1-x)Ti2xO7 were investigated in this work. Y2Mo2(1-x)Ti2xO7 maintains the pyrochlore structure, but lattice constants are observed to decrease continuously with the Ti4+ doping. The magnetic measurements indicate a magnetic phase transition at low temperature for all Ti-doped samples, and the Ti4+ doping suppresses the transition temperature. This is ascribed to the diluted effect of nonmagnetic Ti4+ substitution of magnetic Mo4+. The heat capacity data confirm that the low-temperature magnetic phase is spin glass in the Ti4+-doped Y2Mo2(1-x)Ti2xO7 system. The M(H) data reveals the coexistence of antiferromagnetic and ferromagnetic interactions at low temperatures.

In this work, the Fe60Pt40 nanoparticles were synthesized through the chemical reduction method by using the Fe(CO)5 and the Pt(acac)2 as the metallic precursor. The particle size of the synthesized FePt nanoparticles was controlled by adjusting the reaction conditions involving of the Fe(CO)5-injecting temperature and the soak time of reaction. The structure, morphology, and magnetic properties of the synthesized FePt nanoparticles were characterized by XRD, TEM, and vibrating sample magnetometer (VSM), respectively. The synthesized nanoparticles exhibit uniform size and good dispersity. The magnetization behaviors indicate that the nanoparticles present the core-shell magnetic structure including the ferromagnetic core part and the spin-disorder shell part. There exists a spin pinning effect of the shell part on the core part. The increase of particle size weakens the spin pinning effect.

Bioinspired Soft Magnetic Composites (SMCs) with nacre-like structure were fabricated using highly planar arranged flaky-Sendust. These SMCs show particularly high permeability and low loss, thus exhibiting great potential for high frequency magnetic components. Due to the high saturation magnetization and permeability of metal soft magnetic materials, it is possible to miniaturize magnetic devices by reducing the total loss, especially the eddy current loss at high frequency. The new SMCs with nacre-like structure exhibited a high permeability of up to 600 at 1 MHz, which was ten times that of common Sendust composites. The total loss decreased to 470.82 and 1162.60 kW/m3 at 100 and 200 kHz, respectively (stimulated at 100 mT), and the maximum magnetic induction increased to 714 mT at 8000 A/m, which was superior to that of ferrites. This outstanding comprehensive property is a result of the anisotropic demagnetizing factor of the flaky particles in a planar arrangement, which can be derived from the Aharoni's formula. The minimum total loss is a result of the balance of hysteresis and eddy current loss for the small thickness, which is below skin depth. In addition, the three-dimensional loss separation characteristic was analyzed using the nonlinear regression method to theoretically evaluate the influencing factors related to the morphology of the materials. This approach provides small, high frequency, and high saturation magnetic devices for switching regulators, photovoltaic inverter boost inductors, and noise filters.

Modified cyanate resins (G-CE) and functionalized silica fibers (K-SFs) were obtained by introducing glycidyl polyhedral oligomeric silsesquioxane (G-POSS) and γ-aminopropyltriethoxy silane coupling agent (KH-550), respectively. G-CE and K-SFs were then used to fabricate K-SFs/G-CE wave-transparent composites. The activation energy of the G-CE blends decreased to 49.80 kJ/mol, which led to a decrease in the curing temperature from 274 °C to 254 °C. The contact angle of the functionalized silica fibers increased considerably to 107.4°; this modified the interfacial compatibility, which enhanced the mechanical properties. The K-SFs/G-CE composite had a maximum flexural strength of 548.1 MPa and flexural modulus of 19.3 GPa, which were increases of 86.7% and 48.5% compared to the corresponding values of SFs/CE composite (flexural strength of 293.5 MPa and flexural modulus of 13.0 GPa). In addition, the e and tanδ of the K-SFs/G-CE composite decreased to 2.63 and 3.3 × 10−3, respectively, which were respective decreases of 6.5% and 23.0% compared with the corresponding values of SFs/CE composite (e of 2.76 and tanδ of 4.6 × 10−3). Hence, the resulting K-SFs/G-CE composites are good candidate materials for high performance wave-transparent composites.

In this paper, zirconia green parts with the binder system containing low density polyethylene (LDPE) were prepared by injection molding. The green parts after solvent and thermal debinding were sintered at 1500 °C for 2 h. The influences of LDPE on solvent debinding were emphatically studied. A new method was proposed to determine the extracting degree of the wax binders in comparison with the common method. The results showed that the solvent removable binders could not be extracted completely during the solvent debinding though the replacement of HDPE with LDPE promoted this process. The extracting degree of the wax binders was about 74–80% and increased with the increase of LDPE contents. In addition, it was also found that microcracks easily occurred in the green parts after the solvent debinding when using LDPE replacing HDPE, which may result in the decrease of the bending strength of the sintered samples.

In this paper, the soft magnetic composite was prepared using a powder metallurgy method with the Fe3O4 and ZrO2 co-coated iron powder which was synthesized though the in-situ hydrothermal method. Energy dispersive spectroscopy (EDS) coupled with X-ray photoelectron spectroscopy (XPS) revealed that the Fe3O4 and ZrO2 were uniformly coated on the surface of iron powders. The addition of ZrO2 in the coating effectively improves the properties of the soft magnetic composite. ZrO2 can further improve the insulating properties, and enhance the thermostability of the coating simultaneously which will lead to resistivity increase and eddy current loss decrease. By controlling the additive amount of zirconium cation and annealing temperature, high magnetic induction of 1.002 T (measured at 8000 A/m), relatively high permeability of 83 (measured at 100 kHz), and low total core loss of 255.2 W/kg (measured at 100 kHz and 50 mT) were achieved. The Fe@ZrO2&Fe3O4 SMCs show high electrical resistivity and saturation induction, which may be widely used in high speed electric motor, transformer, inductance and switching power supply.

In this work, we investigated the effects of heat treatment and lubricant on the magnetic properties of iron-based soft magnetic composites by one-pot synthesis method. Scanning electron microscopy (SEM) revealed that the surface of the coated Fe powder was coated with different thickness of Al2O3 insulating layer. The experiment results indicated that using lubricant in the coated iron-based compacts presented higher permeability, higher resistivity, lower core loss over the wide frequency range compared with those without using lubricant after heat treatment at 773 K. The above effects would be reduced with the increase of the thickness of the alumina coating. As the heat treatment temperature raised from 573 K to 773 K and even higher 873 K, zinc stearate continued to decompose, and its decomposition product carbon reacted with the iron oxide of the thinner coating. As a result, the frequency stability of the permeability decreased especially at high frequencies, the resistivity decreased significantly, and the eddy current loss increased significantly. When the alumina insulation layer became thick, the effects of zinc stearate and its leaving carbon after decomposition on the properties of the pressed magnet decreased.

Polyvinyl butyral (PVB) was used in the Al(OH)3/carbon black/ethanol slurries by the three-roll mixing to prepare AlN powder using the carbothermal reduction–nitridation (CRN) process in the experiments. The effects of PVB addition on the synthesis of AlN powder were studied by viscosity, tap density, XRD, SEM and TG measurements. The results showed that the PVB layer covering on the surface of Al(OH)3 particles reduced the viscosity of Al(OH)3/carbon/ethanol slurry and increased the dispersion homogeneity of Al(OH)3/carbon raw powder. The tap densities of the Al(OH)3/carbon mixtures after three-roll milling could be increased with the increase in PVB addition. In the CRN process, most of the PVB covering Al(OH)3 particles evaporated and supplied the passage for nitrogen removal to the particles. Based on the experimental data, the role of PVB on the mixing and CRN process was discussed.

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 (Pcv) 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.

Ultrafine spherical Fe 2 O 3 powders with controllable morphology and crystal phase were synthesized by ultrasonic spray pyrolysis. In this experiment, we chose three common ferric salts (Fe(NO 3 ) 3 ·9H 2 O, FeSO 4 ·7H 2 O or FeCl 2 ·4H 2 O) as precursor solution and regulated the concentration of chlorine ion (Cl − ) in precursor solution to produce Fe 2 O 3 particles. The morphology, crystal structure and magnetic property of prepared Fe 2 O 3 particles were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vibrating sample magnetometer (VSM). The diameter of the obtained Fe 2 O 3 products ranged from 0.2 to 2 μm. And the product obtained from FeCl 2 precursor solution was magnetic, which was composed of hexagonal α-Fe 2 O 3 and cubic γ-Fe 2 O 3 from XRD results. We also calculated the weight percent of α-Fe 2 O 3 and γ-Fe 2 O 3 in the product through XRD quantitative analysis. However, with the addition of Cl − in Fe(NO 3 ) 3 or FeSO 4 precursor solution, the products turned from non-magnetic to magnetic, whose pure α-Fe 2 O 3 phase became to α-Fe 2 O 3 and γ-Fe 2 O 3 multi-phase. Besides, the weight percent of γ-Fe 2 O 3 and the amount of M s increased with the Cl − concentration in precursor solution improving. According to the research, it can be inferred that the presence of Cl − inhibits the phase transition of γ-Fe 2 O 3 to α-Fe 2 O 3 at high temperature.

In this work, the structural and magnetic properties in ZnCr2−xGaxO4 were investigated. In ZnCr2−xGaxO4, Ga3+ ions substitute partial Cr3+ ions and occupy the B sites. ZnCr2O4 undergoes a paramagnetic-antiferromagnetic transition at 12 K. In ZnCr2−xGaxO4, the antiferromagnetic short-range correlation occurs below 60 K above $T_{\mathrm {N}}$ . The Ga3+ doping weakens the antiferromagnetic nearest-neighbor exchange interaction (J1) and induces ferromagnetic next-nearest-neighbor exchange interaction (J2) among the B site magnetic ions. The generation of the ferromagnetic J2 is ascribed to structure distortion induced by the Ga3+ doping.

This paper investigates the structure and magnetic properties of Ni-Cu-Zn ferrite-silicone coated iron-based soft magnetic composites (SMCs). Scanning electron microscopy coupled with a energy-dispersive spectroscopy (EDS) analysis revealed that the Ni-Cu-Zn ferrite and silicone resin were uniformly coated on the surface of iron powders. By controlling the composition of the coating layer, low total core loss of 97.7 mW/cm3 (eddy current loss of 48 mW/cm3, hysteresis loss of 49.7 mW/cm3, measured at 100 kHz and 0.02 T) and relatively high effective permeability of 72.5 (measured at 100 kHz) were achieved. In addition, the as-prepared SMCs displayed higher electrical resistivity, good magnetic characteristics over a wide range of frequencies (20–200 kHz) and ideal the D-C bias properties (more than 75% at H = 50 Oe). Furthermore, higher elastic modulus and hardness of SMCs, which means that the coating layer has good mechanical properties and is not easily damaged during the pressing process, were obtained in this paper. The results of this work indicate that the Ni-Cu-Zn ferrite-silicone coated SMCs have desirable properties which would make them suitable for application in the fields of the electric-magnetic switching devices, such as inductance coils, transformer cores, synchronous electric motors and resonant inductors.

A iron-based soft magnetic composite (SMC) has been prepared by powder metallurgy method with the Fe@Fe 3 O 4 powder of in situ surface oxidation. Effects of the in situ surface oxidized temperature and the annealing temperature on the magnetic properties of the SMC have been investigated from 400 °C to 650 °C. The powder morphology and the phase were tested by scanning electron microscopy (SEM) and the X-ray diffraction (XRD). It shows that the surface of the iron particle contains a thin insulating layer of Fe 3 O 4 which dramatically decreases the core loss and holds the high permeability about 100 and B s . The mechanical properties of the bulk samples were carried out using a nanoindentation. Higher annealing temperature destroys the Fe 3 O 4 insulating layer, resulting in the decrease of the electrical resistivity from 78.3 to 4.61 mΩ·cm as well as the magnetic permeability and its frequency stability. The coated powder can be obtained by surface oxidation at 250 °C. The SMC annealed at the temperature of 450 °C exhibits excellent magnetic and mechanical properties which is suitable for the electric-magnetic switching device, such as inductance coils, transformer cores, synchronous electric motors and resonant inductors.

FeSiCr/PA6 composites were prepared by injection molding using the FeSiCr powders modified by different phosphating agents and KH550 coupling agent. The resistivity, impact strength, magnetic permeability and magnetic loss of the FeSiCr/PA6 composites were measured. The morphologies of different FeSiCr powders and the FeSiCr/PA6 composites were also observed by scanning electron microscope (SEM). The results showed that 1-Hydroxyethylidene-1,1-diphosphonic acid, phytic acid and H3PO4 could improve the electrical resistivity of FeSiCr powders by forming the dense phosphating layer except diphenylphosphinic acid. However, the resistivity of FeSiCr/PA6 composites using the FeSiCr powders treated by all the four phosphating agents had no obvious increase though the phosphating layer on the surface of FeSiCr powder came into being. The nylon insulation layer had much stronger influence than the phosphating layer on electrical resistivity of the composites. After adding appropriate KH550 coupling agent, the impact strengths of FeSiCr/PA6 composites were significantly improved, which may be associated with the tiny gap between FeSiCr powder and PA6 matrix. The effects of the phosphating agents on the magnetic permeability and loss of the FeSiCr/PA6 were small and the mechanism were also discussed.

We investigated the magnetic properties of a geometrically frustrated magnet of ZnFe2O4 nanoparticles by carrying out the comprehensive measurements of dc magnetization and ac susceptibility. Spin glass is confirmed to occur in this weakly Fe(Zn)-ionic-inversed sample. The common characteristics of spin glass including the aging, the memory, and the rejuvenation effects were observed. By using the critical-power law to study the spin dynamics, the spin-glass transition temperature Tg is obtained to be 18 K and the dynamic exponent zν is 8.0. The weak exchange interaction disorder introduced by the ferrimagnetic JAB interaction, together with the weak nonmagnetic dilute disorder induced by the ionic inversion, is responsible for the formation of spin glass in the ZnFe2O4 nanoparticles.

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.

Powder injection molding (PIM) opens new possibilities to process complex Sr-ferrite components for magnetic applications. In the present study, new binder system with the addition of microcrystalline wax (MW) was used for the Sr-ferrite powder injection molding. The optimum binder composition was determined based on rheological measurement, mircrostructure observation by SEM, thermal change by DSC and debinding process. The results indicated that MW with 10 vol.% addition in the binder system containing high density polyethylene (HDPE), paraffin wax (PW) and stearic acid (SA) decreases the defects of the green parts after solvent debinding because the distribution of the binder system between the Sr-ferrite particles becomes more homogeneous. Using the proper binder system containing MW, the defect-free and dense Sr-ferrite ceramics can be prepared after solvent and thermal debinding and sintering. Based on the experimental results, the effects of MW microcrystalline wax on the solvent debinding of the Sr-ferrite ceramics were detailed discussed.

In order to achieve a broad bandwidth absorber at high frequency, the composites of M-type ferrite BaCo 1.0 Ti 1.0 Fe 10 O 19 (BaM) with flaked carbonyl iron powders (CIP) and flaked Fe 50 Ni 50 were prepared to optimize the surface impedance in broadband frequency, respectively. The diameter of the flaked carbonyl iron powders (CIP) and Fe 50 Ni 50 is in the range of 5–10 µm and 10–20 µm and the thickness of the CIP and Fe 50 Ni 50 is close to 200 nm and 400 nm, respectively. The complex permeability and permittivity show that the addition of BaM obviously reduces the values of real part of permittivity and imaginary part of the permeability which can enhance the matched-wave-impedance. The absorption bands less than −10 dB of CIP-BaM and FeNi-BaM absorber approach to 5.5 GHz (5.7–11.2 GHz) and 7 GHz (11–18 GHz) at 1.5 mm. However, the bands of CIP and FeNi are only 1.9 GHz (4.7–6.6 GHz) and 2.1 GHz (4.0–6.1 GHz). Hence, the electromagnetic match property is greatly improved by BaM ferrites, and this composite shows a broaden absorption band.

Using the plasmonic metasurface, we have designed a highly efficient solar ray absorber by tailoring the thickness of the metallic arrays. The geometric-dependent local surface plasmon and concomitant local enhanced electric field are excited, leading to the decay of internal plasmon into energetic electron-hole pair. The architectures of the metasurface deposited on and embedded in the GaAs film have been investigated to exploit the potential of the surface plasmonic. The peak absorbance of the deposited one increases monotonically from about 0.52 at the metasurface thickness of 5 nm to 0.86 at that of 60 nm. While the absorption intensity for the embedded one reaches to 0.92 at the metasurface thickness of 10 nm and further increases to near unity as thickness increases to 30 and 60 nm. The average absorption in the whole spectrum shows that the efficiency of the embedded one is superior to the deposited one. This design is of high economic competitiveness for photovoltaic applications and can be used in complex material system for multifunction including energy harvest and sensor device.

M-type strontium hexaferrites with the chemical composition of Sr1−x−x′LaxCax′Fe2n−yCoyOα 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.

In this study, thin Cu2O films were first produced on a Cu foil by cathodic electro-deposition at different pH values. Then the Cu2O side of the Cu foil was closely attached to an Al2O3 ceramic substrate and heated to 1075 °C under N2 atmosphere. The effect of the pH value on the microstructure of the Cu2O film was investigated by scanning electron microscopy (SEM). The shape of the Cu2O grains changed from a 4-sided pyramid to a triangular prism to a 3-faced pyramid when increasing the pH value from 9 to 11 and 12, respectively. The X-ray diffraction (XRD) results showed that both CuAlO2 and CuAl2O4 were formed at the Cu/Al2O3 interface after reacting for 4 h, in contrast to results reported in previous papers. When the bonding time was extended to 7 h, discontinuous interfacial reaction products were found on the cross-section of the Cu/Al2O3 interface. The effect of the Cu2O morphology on the bonding strength of the Cu/Al2O3 was discussed considering the results of the flexural strength tests, and the results indicated that a uniform and dense Cu2O morphology would be beneficial for improving the bonding strength during the metallization process.

A new reduction–diffusion method for preparing submicron-sized Sm2Fe17N3 was developed. First, submicron-sized α-Fe/Sm2O3 composite precursors with good dispersibility were prepared directly by ultrasonic spray pyrolysis and hydrogen reduction (USP-HR). Then, the precursor was successfully converted into Sm2Fe17N3 powder by Ca reduction–diffusion and nitridation. The results displayed that the precursor prepared by USP-HR was a monodisperse homogeneous composite of spherical particles of α-Fe and Sm2O3. α-Fe and Sm2O3 exist in an intercalated structure in the composite spherical particles. This creates conditions for the preparation of ultrafine Sm2Fe17N3 particles with uniform sizes and dispersity. The results show that Sm2Fe17N3 is a single-phase, composed of submicron-sized particles with no other impurity phases. The physical property measurement system shows that the coercivity of 0.616 ± 0.347 µm particles reaches 14.7 kOe.

In this work, the effects of the Al2O3 insulating coating and surfactant on magnetic properties of the iron powders coated with Al2O3 by one-pot synthesis method were investigated. The morphology, phase composition and magnetoelectric properties of iron powders coated with Al2O3 were tested respectively. Compared with uncoated iron powder, the composite powder of Al2O3 insulating layer not only has better permeability stability in the frequency range of 5–300 kHz, but also has lower core loss, especially eddy current loss in the frequency range of 5–100 kHz. The surface of iron powder modified by surfactant will change crystallization process of aluminum hydroxide. After the addition of dodecyl trimethyl ammonium bromide (DTAB) as the surfactant, the Al2O3 insulating coating becomes denser and smoother, and the core loss of coated powders is further reduced.

In this paper, Fe-based soft magnetic composites (SMCs) hydrothermally coated with lithium aluminum oxide (Li–Al–O) with better magnetic properties and lower core losses than Al2O3 coated layers have be investigated. The microstructure and composition of the coating and magnetic properties of the composites were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and B–H curve analyzer. Those results revealed that when Li2CO3 was added to the aluminum nitrate solution, the originally formed Al2O3 coating layer converted to a layer with a mixture of several lithium aluminum oxides. Fe-based SMCs coated with lithium aluminum oxide showed lower core losses, higher and stable effective permeability as compared with iron rings coated with Al2O3, especially in high frequency range of 100–300 kHz.

The method of magnetic stirring in fluid-bed galvanic deposits was used for cladding low-melting-point metallic tins onto the surface of rapid quenching Nd–Fe–B magnetic powders. This form of bonding was also used to make Nd–Fe–B/Sn composite magnets by warm pressing at 300 °C. The tin-plating layers of the Nd–Fe–B magnetic particles were observed by scanning electron microscope (SEM). The magnetic properties of the coated and uncoated powders were examined by vibrating sample magnetometer (VSM), respectively. Furthermore, both the compressive strength and magnetic properties of Sn-coated Nd–Fe–B/Sn-bonded magnets were measured. The results indicate that not only the tin plated and magnetic powders were bonded closely, but also the content of tin-plated layers can be controlled by the electrical current. The (BH)max and Br value of magnetic powders decrease with the increasing content of plated tin. An increase in the tin-plated content results in an elevation in magnetic properties of composite m...

Sm2Fe17 alloy is the intermediate material for the preparation of Sm2Fe17N x (x ≈ 3); thus, the synthesis of pure Sm2Fe17 mother alloy is the key to obtaining high-performance Sm2Fe17N x . Reduction–diffusion (R–D) is a cost-effective method. In this study, the R–D process of synthesizing Sm2Fe17 was analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray fluorescence (XRF). Furthermore, the influences of the tightness of compacted reactants, the compensation amount of Sm2O3, and the particle size of Fe on the formation of Sm2Fe17 were discussed from the aspects of the three raw materials. The results show that Sm reduced from Sm2O3 reacts with Fe particles to form intermetallic compound Sm2Fe17 directly in the R–D reaction process of preparing Sm2Fe17; the generation of Sm and its migration to the surface of Fe particles control the reaction rate; a proper tightness of compacted reactants is necessary for ensuring the purity of Sm2Fe17 product; pure Sm2Fe17 can be obtained when the compensation of Sm2O3 is 33 % of the stoichiometry; and the sufficiency of the reaction improves with the decrease in the size of Fe powders under the same reaction condition.

To study the magnetic interaction between Mn3+ and Ru4+, we designed and synthesized a series of samples La1−x Sr x Mn1−x Ru x O3 (0 ≤x ≤ 0.80), in which Mn and Ru ions remain as Mn3+ and Ru4+, respectively. The structural, magnetic, and transport properties of polycrystalline La1−x Sr x Mn1−x Ru x O3 (0 ≤x ≤ 0.80) were investigated. Measurements of magnetization show that Ru4+ substitution induces and enhances ferromagnetism as x≤ 0.30. According to measurements of electronic conductivity, all doping samples show the insulating behaviors without metal-insulation transition. However, with increasing Ru4+ substitution, resistivity decreases and a shoulder appears in the ρ(T) curves at around corresponding Curie temperature for 0.10 ≤ x ≤ 0.40. A large magnetoresistance effect is also observed in La0.60Sr0.40Mn0.60Ru0.40O3. All these phenomena is confirmed to be related with the double exchange interaction between Mn3+ and Ru4+ ions.

Aluminum nitride ceramic powders were prepared by self-propagating high temperature synthesis using the large spherical aluminum powders as reactants. The sintering behavior of the as-received powder was characterized using the conventional liquid sintering method. X-ray diffraction and scanning electron microscope were used to detect the phase compositions and observe the morphologies of the products. The results show that the large aluminum particles evolve into the aggregates consisting of many small AlN particles with spherical shape and stable size. The small spherical particles after deagglomeration by ball milling can be densely sintered at 1830 °C for 2 h. The mechanism that the Al liquid formed at the high temperature repeatedly flows and reacts with the coming nitrogen gas was proposed to explain the evolution from the large aluminum particle into the aggregate with small particles. Some further experiments were also carried out to demonstrate this mechanism.

In this study, NdFe 12 N x magnetic powders were modified using 3-aminopropyltriethoxysilane coupling agent (KH550). The phase compositions, antioxidant properties, and magnetic properties of NdFe 12 N x magnetic powder before and after surface modification were investigated by X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometer, respectively. The possible mechanism of the surface modification was also discussed. The results showed that the silane coating prevented the NdFe 12 N x powders from corrosion and oxidation, thereby maintaining the durability and long term stability. Although the surface modification using KH550 reduced the magnetic properties to a certain extent, it played an important role in improving the oxidation resistance of NdFe 12 N x powders.

Magnetic properties of the Zn0.80Ni0.20Fe2O4 nanoparticle were investigated by measuring the dc magnetization and ac susceptibility. The ferrimagnetic phase forms below 225 K. Through analyzing the relationship between the transition temperature and frequency in the ac susceptibility, it is confirmed that the magnetic dipolar interaction between ferrimagnetic nanoparticles causes a cluster-glass behavior. In the low-temperature region (below 90 K), an antiferromagnetic phase is found to coexist with the ferrimagnetic phase. The antiferromagnetic interaction between the B-site Fe ions plays an important role in the formation of the antiferromagnetic phase.

In this work, a double coating protection technique of phosphating treatment and copper plating was made to improve the corrosion resistance of sintered Nd-Fe-B magnets. In other words, the intergranular region of sintered Nd-Fe-B is allowed to generate passive phosphate conversion coating through phosphating treatment, followed by the copper coating on the surface of sintered Nd-Fe-B. The morphology and corrosion resistance of the phosphated sintered Nd-Fe-B were observed using SEM and electrochemical method respectively. The phosphate conversion coating was formed more preferably on the intergranular region of sintered Nd-Fe-B than on the main crystal region; just after a short time of phosphating treatment, the intergranular region of sintered Nd-Fe-B has been covered by the phosphate conversion coating and the corrosion resistance is significantly improved. With the synergistic protection of the intergranular phosphorization and the followed copper electrodeposition, the corrosion resistance of the sintered Nd-Fe-B is significantly better than that with a single phosphate film or single plating protection. (C) 2014 Elsevier B.V. All rights reserved.

This article reports the chemical deposition of silver shells on the surface of micro-carbon spheres. The structure, morphology and composition were characterized by scanning electron microscopy and X-ray diffraction. Carbon spheres were oxidized with concentrated nitric acid and sulfuric acid for the surface hydrophilic modifier. Subsequently Carbon spheres were coupled with KH-550 in order to grafting NH2 groups, which is important to the site-selective deposition of silver during sensitization and activation process. The dispersible Ag/C core–shell composite could be systematically controlled through adding appropriate PVP and adjusting modest pH value in the deposition process. The XRD and SEM results show that the silver particles can completely coat the carbon spheres and the particle size of the silver shell on the surface of carbon core is 24.8 nm.

In this paper, the relationship of the frequency-dependent magnetic permeability, magnetic loss, and DC-bias of a soft magnetic composite was analyzed. The permeability is divided into a domain wall movement component at low frequencies and a spin-rotation part at high frequencies. The resonance-frequency increases when the pressure decreases and, simultaneously, the permeability also decreases following the Snoek limit. Magnetic loss is separated into hysteresis loss, eddy-current loss, and excess loss, which is found to closely relate to the density of the powder core. The DC-bias properties of the composite tend to deteriorate slightly with the density increase. This is due to a decrease in the gap between the particles, which is associated with the pinning of the domain wall movement and coercivity. It is found that DC-bias is positively correlated with hysteresis loss and excess loss with respect to coercivity and pinning of the movable domain-wall. These results provide insights into the soft magnetic performance of soft magnetic composites, particularly with respect to compact, high-DC applications with high frequency and high magnetic saturation for high-power supply.

The influence of NH4 + on the preparation of carbonaceous spheres by a hydrothermal process was studied. A scanning electronic microscope and laser particle size analyzer were used to observe and measure the morphology and size distribution of the spheres. Fourier transform infrared spectroscopy was used to analyze the functional groups of the spheres. The results show that the addition of NH4 + has a significant influence on the morphology, size, and yield of the spheres. The slight addition of NH4 + greatly increases the diameter of the spheres and simultaneously improves their dispersion. With the change of NH4 + concentrations, the as-received spheres have sizes from 0.2 to 20 μm in diameter. The Fourier transform infrared spectroscopy results indicate that the C = O group disappears in the samples with NH4 + addition, different from the obvious peak at 1700.2 and 1305.6 cm−1 in the samples with no NH4 + addition. A possible mechanism of the formation and growth of the spheres with the addition of NH4 + is also proposed in the paper.

A 50 μm Al–Cr coating on NdFeB sintered magnets was prepared through dipping in solution, shaking dry and heating at 300 °C. The morphology and composition of the Al–Cr coating were investigated with scanning electron microscope, energy dispersive spectrometer and X-ray diffraction. The corrosion resistance of NdFeB sintered magnets with and without the Al–Cr coating was analyzed by normal salt spray, polarization curves and electrochemical impedance spectroscopy. The magnetic properties were measured with a hysteresis loop tracer. The results show that the Al–Cr coating forms an overlapping structure and Al flakes lie nearly parallel to the substrate, which improves the anticorrosion and increases normal salt spray test from 10 to 100 h. The corrosion potential of NdFeB sintered magnets with and without the Al–Cr coating moves positively from −0.67 to −0.48 V, which is in accordance with Nyquist and Bode plots. The Al–Cr coating has little influence on the magnetic properties of the NdFeB sintered magnets.

A strontium ferrite powder added with trace of Bi2O3 was prepared by the conventional high-temperature solid phase reaction. The effects of Bi2O3 addition on the morphology of Sr-ferrite particles fired at different temperatures and times were investigated. The results show that a small quantity of Bi2O3 addition accelerates the reaction of SrO and Fe2O3 to form SrM ferrite and obviously improves the morphology and size of the strontium ferrite particles. A possible mechanism was proposed to interpret the influence of trace of Bi2O3 addition on the morphology of strontium ferrite particles.

In this paper, we present a design, simulation and experimental measurement of a cross array metamaterial absorber (MMA) based on the flaked Carbonyl iron powder (CIP) filled rubber plate in the microwave regime. The metamaterial absorber is a layered structure consisting of multilayer periodic cross electric resonators, magnetic rubber plate and the ground metal plate. The MMA exhibits dual band absorbing property and the absorption can be tuned from 1∼8GHz in the same thickness depending on the dimension and position of the cross arrays. The obviously broadened absorbing band of the designed structure is a result of the synergistic effects of the electrical resonance of the cross arrays and intrinsic absorption of the magnetic layer. The polarization and oblique incident angle in TE and TM model are also investigated in detail to explore the absorbing mechanisms. The resonance current of the cross array can excite the enhanced local magnetic field and dielectric field which can promote the absorption. The measurement results are basically consistent with the simulations but the absorbing peaks move a little bit to higher frequency for the reason that the surface oxidation of the flaked CIP in the preparation process.

Corrosion characters of Nd-Fe-B-sintered magnets in remanence states in sulfuric acid (H2SO4), phosphoric acid (H3PO4), sodium hydroxide (NaOH), and sodium chloride (NaCl) solutions have been investigated, respectively. Experimentally, the study was carried out with weight-loss and electrochemical potentiodynamic polarization tests. As the results showed, electrochemical reaction mechanism of Nd-Fe-B-sintered magnets in different solutions was not changed by the remanence state. But, corrosion of the magnets was accelerated in H2SO4 and NaCl solutions, owing to the formation of an occluded corrosion cell with self-catalyzing effect. In H3PO4 and NaOH solutions, however, Nd-Fe-B-sintered magnets were passivated and corrosion was decelerated. The remanence state changed the electric double-layer structure on the magnet/electrolyte interface, which was responsible for the production of the magneto overpotential and the change of electrochemical corrosion rate of Nd-Fe-B-sintered magnets.