Search

The c-axis oriented hcp-Co81Ir19 magnetic films were prepared on different seed layers (Ni, Cu, Ir, Pt, Au and No seed). It was systematically investigated that the factors of surface free energy and strain energy have impact on the orientation and defects and/or internal stress with increasing the lattice mismatches ratio. Moreover, the initial permeability and the natural resonance frequency were discussed in great detail by using the comparison between calculated values and experiment values. We have found that the almost unchanged 4πM s and μi are not affected, while the changed H c , intrinsic K grain and fr are strongly dependent on a seed layer and the seed layer material. Moreover, the extracted damping constant is sensitive to the defects and/or internal stress and the orientation of grains. Therefore, the soft magnetic properties and microwave properties are adjusted and optimized by the seed layers with different material.

In this work, we present detailed $^{57}$Fe M\"ossbauer spectroscopy investigations of (Co$_{0.97}$$^{57}$Fe$_{0.03}$)$_{4}$Nb$_{2}$O$_{9}$ compound to study its possible magnetic structures. We have shown that the previously reported magnetic structures can not satisfactorily describe our low temperature M\"ossbauer spectra. Therefore, in combination with theoretical calculations, we have proposed a modulated helicoidal magnetic structure that can be used to simulate the whole series of our low temperature M\"ossbauer spectra. Our results suggest that the combination of previously reported different magnetic structures are only approximations of the average magnetic structure from our modulated helicoidal model. We anticipate that the proposed modulated non-collinear magnetic structure might shed light on the understanding of the complex magnetoelectric effects observed in this system., Comment: To be published in Journal of Magnetism and Magnetic Materials; online version: https://www.sciencedirect.com/science/article/pii/S0304885323003876 Or DOI link: https://doi.org/10.1016/j.jmmm.2023.170738

In this study, to investigate the effect of volume concentration on core loss in the high frequency band (∼MHz), easy-plane soft magnetic composites (SMCs) of FeSiAl particles with different volume concentrations were prepared successfully by magnetic field orientation. The permeability of the SMCs was decomposed into the domain wall component and the spin component and was well simulated. The core loss was successfully decomposed into hysteresis loss, eddy current loss and anomalous loss. It was shown that the permeability of the SMCs was continuously improved as the volume concentration of FeSiAl in the SMCs increased, while the core loss decreased first and then increased due to the different performances of the hysteresis loss, eddy current loss, and anomalous loss. Samples with a permeability of 310 exhibited the lowest core loss of 399 kW m−3 (f = 3 MHz, 10 mT). The results indicated that there is an optimal volume concentration at which SMCs have a relatively high permeability and minimum core loss.

The miniaturization and high frequency of future electromagnetic devices require soft magnetic composites with high permeability, high working frequency, and low core loss. In this work, easy-plane amorphous FeSiBCr powders with a thickness of approximately 1–2 μm are obtained by planetary ball milling, and are successfully fabricated into an arranged soft magnetic composite by using a uniform magnetic field. The complex permeability spectrums of the composites are measured and analyzed. Due to the planar distribution of easy magnetization axes, the amorphous easy-plane FeSiBCr/Si-resin composite shows a permeability of 31 at 1 MHz. The core loss of the samples is measured from 100 KHz to 5 MHz and is discussed in detail. The loss-separated results illustrate that the eddy current loss and excess loss can be effectively reduced in the amorphous easy-plane FeSiBCr/Si-resin composite. These results indicate that, compared with an amorphous non-easy-plane FeSiBCr/Si-resin composite, the permeability of the amorphous easy-plane FeSiBCr/Si-resin composite is effectively improved and the core loss is reduced, making it promising for high-frequency applications.

Intelligent machines are knowledge systems with unique knowledge structure and function. In this paper, we discuss issues including the characteristics and forms of machine knowledge, the relationship between knowledge and human cognition, and the approach to acquire machine knowledge. These issues are of great significance to the development of artificial intelligence.

Herein, we attempted to prepare MoS2/Fe@Fe3O4 nanocomposites capable of strongly absorbing broadband incident electromagnetic (EM) radiation and probed the effects of their composition on complex permittivity and permeability at 2–18 GHz. Calculations of normal-incidence reflection losses (RLs) based on EM parameters revealed that the Fe@Fe3O4 to MoS2 mass ratio strongly influenced the absorption peak intensity and bandwidth. Specifically, an RL peak of −31.8 dB@15.3 GHz and a bandwidth (RL

Magnetic nanostructures with flux-closure state or single-domain state have widespread application in diverse memory devices. However, an insight into the modulation of these variable states within one specific magnetic material is rarely reported but still needed. Herein, these micromagnetic configurations within prototypical cobalt ferrite (CoFe2O4) nanostructures in different size and dimension were studied by modulating the assembly of CoFe2O4 building blocks. We find that the CoFe2O4 nanowire (NW) has a multidomain structure when the diameter is about 90 nm, in which the domain walls (DWs) locate preferentially at the grain boundary and can convert to single-domain state when the diameter is reduced. Alternatively, a flux-closure domain state is obtained when the CoFe2O4 nanostructure changes from NW to nanosheet (NS), where the DWs location depends on the overall shape of NS. In addition, we further confirm that the magnetic anisotropy and magnetostatic energy are two main factors affecting the micromagnetic configuration in CoFe2O4 nanostructures by crystallographic analysis and micromagnetic simulations. Our experimental and simulation results demonstrate that the modulation of morphology and dimension are efficient to tailor the micromagnetic configuration in magnetic nanostructures.

To satisfy impedance matching at low frequencies and obtain high microwave absorption performance, easy-plane anisotropy Fe–Si powders coated with SiO2 were produced by a ball milling technique and a chemical deposition method. Then, a scanning electron microscope, a transmission electron microscope, an X-ray photoelectron spectrometer, an X-ray diffractometer, a Mossbauer spectrometer, a vibrating sample magnetometer, and a vector network analyzer were used to characterize the samples. Compared to easy-plane anisotropy Fe–Si powders without surface modification, the dielectric constant of easy-plane anisotropy Fe–Si powders with SiO2 coating decreased dramatically and the microwave absorption performance was improved significantly. The reflection loss peak reached − 10 dB when the thickness was 1.4 mm and even reached − 34 dB when the thickness was 4.5 mm, exhibiting great potential for application in thin absorbers working in the frequency range of 0.1–4 GHz. In addition, the microwave absorption performance at oblique incidence was also investigated. A reflection loss peak of − 30 dB was obtained when the incident angle was 30°, and a reflection loss peak of more than − 10 dB can still be obtained even when the incident angle was 80°. The results show that the easy-plane anisotropy Fe–Si powders with SiO2 coating still possess high microwave absorption performance at oblique incidence.

Planar hexaferrite BaCo2Fe16O27 was prepared by a simple adsorbent combustion method. The BaCo2Fe16O27/paraffin composite with 45 vol% particles was subjected to a rotational orientation process in an external magnetic field, resulting in highly-oriented BaCo2Fe16O27 composite with an alignment degree of 0.88. The oriented composite showed higher permeability in both real and imaginary parts as compared to its random counterpart. Significant enhancement of microwave absorbing performance was obtained for the oriented composite in 8–18 GHz due to the enhanced impedance matching and magnetic loss, displaying much stronger absorption and greater bandwidth (≤−10 dB) than the random composite. Moreover, a thinner matching thickness can be achieved for a given matching frequency through the alignment of easy magnetization planes. The results showed that the c-plane alignment process holds promises for rational design of lightweight magnetic absorbers with planar anisotropy.

In this study, thin Pr2Co17 flakes fractured along c crystal plane are successfully prepared by a surfactant-assisted high energy ball-milling technology and then oxidized by hydrogen peroxide (H2O2). The complex permittivity and permeability of the unoxidized and oxidized Pr2Co17 flakes/epoxy composites are measured. The measured results show that the oxidation of H2O2 can effectively decrease the permittivity and simultaneously suppress the eddy. For the oxidized sample with 40 vol% Pr2Co17, the real permeability at 8.2 GHz and 12.4 GHz can reach 1.65 and 1.42, respectively, and the natural resonance frequency can reach 11.0 GHz. If used as a microwave absorber, the oxidized sample with 20 vol% Pr2Co17 flakes exhibits a very excellent microwave absorption performance in x-band when the absorber thickness t is very thin (1.3 mm

The complex permeability and permittivity of the easy-plane anisotropic Co/polyimide composite at high temperature (293–673 K) in X band were measured. The results show that both the complex permeability and permittivity increase with the increase of temperature in the measured temperature range. The calculated absorption properties display that the intensity of the reflection loss (RL) peak first increases and then decreases with the increase of temperature, and reaches the maximum (−52 dB) at 523 K. At each temperature, the composite can achieve the RL exceeding −10 dB in the whole X band. The composite can even work stably for more than 20 min with the excellent absorption performance under 673 K. In addition, the RL performance of the composite at high temperature is better than that at room temperature.

Co@C nanofibers have been prepared by an electrospinning technique. Uniform morphology of the nanofibers and good dispersion of the magnetic cobalt nanoparticles in the carbon fiber frame were confirmed by field-emission scanning electron microscopy and high-resolution transmission electron microscopy. The electromagnetic parameters of a composite absorber composed of Co@C nanofibers/paraffin were measured from 2 GHz to 15 GHz. The electromagnetic wave absorption properties were simulated and investigated in the case of normal and oblique incidence. In the normal case, the absorber achieved absorption performance of − 40 dB at 7.1 GHz. When the angle of incidence was increased to 60°, the absorption effect with reflection loss (RL) exceeding − 10 dB could still be obtained. These results demonstrate that the reported Co@C nanofiber absorber exhibits excellent absorption performance over a wide range of angle of incidence.

$^{57}$Fe M\"ossbauer spectra were measured at different temperatures between 5.9 K and 300 K on the recently discovered self-doped superconducting RbGd$_2$Fe$_4$As$_4$O$_2$ with T$_c$ as high as 35 K. Singlet pattern was observed down to the lowest temperature measured in this work, indicating the absence of static magnetic order on the Fe site. The intermediate isomer shift in comparison with that of the samples RbFe$_2$As$_2$ and GdFeAsO confirms the self doping induced local electronic structure change. Surprisingly, we observe two magnetic fluctuation induced spectral broadenings below $\sim$15 K and $\sim$100 K which are believed to be originated from the transferred magnetic fluctuations of the Gd$^{3+}$ moments and that of the magnetic fluctuations of the Fe atoms, respectively., Comment: 6 pages, 6 figures, 1 table

There is a widely observed phenomenon in the microwave absorption field that an absorber always exhibits good oblique incidence absorption capacity if it has high performance at normal incidence. However, if a certain angle is exceeded, this kind of effective absorptive capacity will no longer be maintained. Besides, an absorber performs differently for incident transverse electric (TE) and transverse magnetic (TM) waves: for the TE case, the absorber can no longer obtain effective absorption; for the TM case, another efficient absorption region was observed at higher frequencies even when the incident angle exceeded 80°. These phenomena are widely found in the literature, which demonstrates that they are caused by physical laws rather than material properties. To demonstrate the underlying reason, in this study, the common spherical carbonyl iron-polyurethane composite absorbers were fabricated as a typical example. Their absorbing performance was investigated via both simulation and experiment. All the phenomena mentioned above were observed, studied in detail by employing the multiple reflection model, and explained quantitatively. Further, along with establishing the underlying mechanism of electromagnetic wave transmission in the absorber, two formulas were deduced to predict: (a) the maximum incident angle for efficient absorption of the TE polarized wave; and (b) the required absorber thickness for obtaining efficient absorption for a large incident angle of the TM polarized wave.

We have synthesized thin Fe3O4 microflakes by a simple hydrothermal method and prepared Fe3O4 microflake–paraffin composites without and with magnetic orientation using the method of simple ultrasonic mixing and rotating samples in a magnetic field. X-ray diffractometer, Mossbauer spectrum, scanning electron microscope and vibrating sample magnetometer were used to characterize the samples. The complex permittivity and permeability of Fe3O4 microflake–paraffin composites without and with magnetic orientation were measured in the frequency range of 0.1–18 GHz by a vector network analyzer using a coaxial method. The reflection loss (RL) was calculated by the measured electromagnetic parameters using transmission line theory. The measurement of electromagnetic parameters shows that magnetic orientation makes the complex permittivity and permeability increase. The calculated RL shows that the Fe3O4 microflake–paraffin composite with magnetic orientation has enhanced microwave absorption properties in the frequency range of 1–3 GHz and the thickness range of 2.9–3.5 mm, indicating that the Fe3O4 microflake–paraffin composite with magnetic orientation is a promising thin microwave absorption material in the L-S band.

In this work, the high frequency and microwave absorption properties of two-dimensional (2D) Sm2Fe14B nanoflakes were investigated. Both planar magnetocrystalline and shape anisotropy was obtained for the 2D Sm2Fe14B nanoflakes prepared via die-upset process, which can effectively increase the effective out-of-plane anisotropy field and improve the high frequency intrinsic magnetization (the product of initial permeability and resonance frequency). The nanoflakes have a diameter of approximately 1–2 μm and a typical thickness of approximately 200 nm. Compared with irregular Sm2Fe14B powder, a higher complex permeability and a lower complex permittivity were obtained for the 2D Sm2Fe14B nanoflakes because of the suppressing eddy effect and the oxidized grain boundary phase (GBP) layer, which facilitates the microwave absorption performance. A minimum RL value reaches −16.9 dB at the perfect matching frequency of 12.1 GHz.

We present detailed investigations of structural and static/dynamic magnetic properties of hydrogenated hcp-Co80 57Fe4Ir16 soft magnetic thin films. Two different kinds of defects, i.e., destructive and non-destructive, were demonstrated by controlling the negative bias voltage of the hydrogenation process. Our results show that the structure and magnetic properties of our sample can be tuned by the density of the induced defects. These results provide better understanding of the hydrogenation effect and thus can be used in the future for materials processing to meet the requirements of different devices.

Magnetic behaviors within nanoscopic materials are being widely explored due to their intriguing performance and widespread applications. Herein, we studied the magnetization reversal mechanism in a unique tubular nickel ferrite (NiFe2O4), in which the building blocks of NiFe2O4 monocrystalline have a face-centered spinel structure and stack along the axial direction of the nanotube. We synthesized this tubular NiFe2O4 through an electrospinning method based on a phase separation process, and then investigated the magnetization reversal process and its relationship with the morphologies using the model of “chain-of-rings” from the micromagnetism theory. This model is developed based on the morphology and crystalline orientation of nanotubes, by which the symmetric fanning mechanism is demonstrated when the angle between the magnetic field and the chain is less than 45.3°. As a result, the simulated coercivity value is confirmed to be 271 Oe, which is close to the experimental value. In addition, the rationality of this model was further verified by the calculation of the effective magnetic anisotropy field. This work is significant for the application of tubular ferrite in the field of nano-devices and fundamental research.

To fully release the potential of wide bandgap (WBG) semiconductors and achieve high energy density and efficiency, a carbonyl iron soft magnetic composite (SMC) with an easy plane-like structure is prepared. Due to this structure, the permeability of the composite increases by 3 times (from 7.5 to 21.5) at 100 MHz compared with to the spherical carbonyl iron SMC, and the permeability changes little at frequencies below 100 MHz. In addition, the natural resonance frequency of the composite shifts to higher frequencies at 1.7 GHz. The total core losses of the composites at 10, 20, and 30 mT are 80.0, 355.3, and 810.7 mW/cm3, respectively, at 500 kHz. Compared with the spherical carbonyl iron SMC, the core loss at 500 kHz is reduced by more than 60%. Therefore, this kind of soft magnetic composite with an easy plane-like structure is a good candidate for unlocking the potential of WBG semiconductors and developing the next-generation power electronics. © 2021 Chinese Physical Society and IOP Publishing Ltd.

A soft magnetic composite (SMC) material with a large aspect ratio is prepared by a ball-milling method. Such SMCs have excellent high-frequency performance such as high permeability, saturation magnetization, and resonance frequency, which makes them have great potential in the field of 5G and high-frequency power devices. The flaky particles with large aspect ratios can effectively reduce eddy current loss and obtain larger permeability. Simultaneously, we also further studied the high-frequency magnetic properties and loss of SMCs with different aspect ratios. We obtained the magnetic spectra of samples with different aspect ratios and then established a loss model for flaky samples under high frequency and performed loss separation for these samples. The relationship between the aspect ratios, permeabilities, and three types of loss after separation is analyzed and discussed. A large aspect ratio can effectively improve the permeability and reduce the eddy current loss, and a high permeability due to a large aspect ratio can also reduce the hysteresis loss. The differentiation of magnetic domain and the variation in the number of domain walls caused by the process of obtaining the large aspect ratio (ball milled), high permeability caused by this process and number of displaced domain walls also affect the excess loss. This provides the possibility for the application of soft magnetic material composites at high frequencies.

The c-axis oriented hcp-Co78Ir22 soft magnetic thin films with in-plane uniaxial anisotropy and negative magnetocrystalline anisotropy were fabricated with substrate temperature at 30 degrees C and 500 degrees C, respectively. Our results further reveal that sputtering under 500 degrees C can obtain a film with better grain structure and higher degree of orientation, which in turn improves the M-s and the magnetocrystalline anisotropy field. As the M-s and the total out-of-plane anisotropy field including the demagnetization field and the magnetocrystalline anisotropy field were enhanced, the high-frequency magnetic parameter (mu(i)-1)f(r) is approximately two times larger than that of the sample fabricated at 30 degrees C. In addition, the damping constant decreases quite a lot with increasing temperature. This work indicates that the high frequency properties can be well adjusted by changing substrate temperature. (C) 2016 Elsevier B.V. All rights reserved.

The microwave magnetic properties of the soft magnetic Y2Fe17Nx (x≈3) particles with easy-plane anisotropy were reported. The high MS and out-of-plane anisotropy result in the high permeability in GHz frequency band. The complex permeability of the Y2Fe17Nx particles/paraffin composite was further enhanced by inducing the easy magnetization planes of the particles to be parallel to each other through a rotational orientation. The calculated reflection loss (RL) properties of the orientated Y2Fe17Nx composite revealed that this composite can be used as high-performance absorber in S band.

This paper presents a model of interface reflection interference in order to determine matching frequency and thickness with minimum reflection loss. It is found that a proper combination of the front-face reflection and back-face reflection is necessary to produce perfect matching, which leads to global minimum reflection loss. The calculated amplitude differences of the front-face reflection and back-face reflection from the derived formula agree well with the intensity variation of the microwave matching absorbing peak.

Broadband absorbing coating in the case of large-angle incidence is rarely studied. In this paper, the high filling ratio graphene-paraffin composite absorbing coatings which are capable of absorbing large-angle incident transverse magnetic (TM) waves in an ultra-wide frequency band were prepared. By increasing the filling ratio, the optimum absorbing angle was found to increase. In particular, the bandwidth of the absorber with 15% mass fraction covers 3.6-18 GHz when the incident angle is 86° at the thickness of 1.5 mm. The dependence of absorbing properties on the thickness of the absorbing coating was also studied. Different from the variation pattern in the case of normal incident, in the case of oblique incidence, with the increase of the thickness, the absorption bandwidth will expand to the low frequency, while the original absorption performance remains unchanged. Through the multi-reflection model, this phenomenon was investigated comprehensively and the underlying physical mechanism of the change of the absorption performance was explained.

We establish a theoretical bimodal model for the complex permeability of flaky soft magnetic composite materials to explain the variability of their initial permeability. The new model is motivated by finding the two natural resonance peaks to be inconsistent with the combination of the domain wall resonance and the natural resonance. In the derivation of the model, two relationships are explored: the first one is the relationship between the number of magnetic domains and the permeability, and the second one is the relationship between the natural resonance and the domain wall resonance. This reveals that the ball milling causes the number of magnetic domains to increase and the maximum initial permeability to exist after 10 h of ball milling. An experiment is conducted to demonstrate the reliability of the proposed model. The experimental results are in good agreement with the theoretical calculations. This new model is of great significance for studying the mechanism and applications of the resonance loss for soft magnetic composite materials in high frequency fields.

Soft magnetic composites (SMCs) are effective as magnetic powder cores in power transformers. Currently, SMCs used in transformers are mostly prepared from NiZn ferrites. One example of this type of material is NiZnCu ferrite, whose working frequency limit is 40 MHz. Above this frequency, its large magnetic loss angle tangent ( tan δ m), approximately equal to 0.29 at 100 MHz, seriously impairs the property of transformers. Generally, the magnetic losses in the MHz frequency band result from eddy-current loss, domain wall resonance, and natural resonance, specifically the high natural resonance loss. A way to decrease it is by increasing the resonance frequency ( f r). However, the increase in f r is very difficult for the uniaxially anisotropic NiZnCu ferrite due to the Snoek limit. We present a composite of oriented Ce2Fe17N3 microflakes and polyurethane in this letter. Although its true permeability is not as high as that of NiZnCu, the f r reaches 7.5 GHz. As a result, the tan δ m at 100 MHz is decreased to 0.015. This indicates that our material has a higher working frequency than NiZnCu and should make fabrication of a 100 MHz transformer possible.

The rapid development of information technology urgently requires magnetic materials with excellent magnetoelectric performance under high frequency (GHz band) conditions. A series of investigations of rare earth-iron intermetallic compounds with planar or cone anisotropy lead to the finding that these compounds have attractive features of high saturation magnetization and high resonance frequency fr. With further research and development, rare earth-iron intermetallic compounds are expected to become a new kind of high frequency soft magnetic material. In contrast to the permanent magnets such as Nd2Fe14B with high uniaxial magnetocrystalline anisotropy field, rare earth-transition metal intermetallics such as R(Fe,X)12, (R,R′)2(Fe,X)14B, (R,R′)2(Fe,X)17, and their nitrides (R,R′ are rare–earth, X is the substitutional elements) can be modified to exhibit planar or cone magnetocrystalline anisotropy, achieving excellent soft magnetic properties of higher fr as well as higher permeability μ i , and thus much higher Snoek limit: f r μ i - 1 . These intermetallics powders/paraffin/resin composites show a maximum reflection loss (RL) between −20 and −70 dB in a wide range of 1–40 GHz, and a large effective absorption bandwidth of 2–10 GHz with a small thickness. Notably, the microwave absorbing performance of the intermetallics samples greatly exceeds the traditional absorbing materials due to their high saturation magnetization and high ratio of the out-of-plane magnetocrystalline anisotropy field to the basal plane anisotropy field. Therefore, rare earth-transition metal intermetallics present an advantage for use as a high-performance thin-layer microwave absorber. They also have great potential to be developed into soft magnetic materials and devices with high performance and high stability at high frequency. It thus opens up broad prospects for technology applications.

With the advent of Fe-As based superconductivity it has become important to study how superconductivity manifests itself in details of 57Fe Mossbauer spectroscopy of conventional, Fe - bearing superconductors. To this end, the iron-based superconductor Lu2Fe3Si5 has been studied by 57Fe Mossbauer spectroscopy over the temperature range from 4.4 K to room temperature with particular attention to the region close to the superconducting transition temperature (Tc = 6.1 K). Consistent with the two crystallographic sites for Fe in this structure, the observed spectra appear to have a pattern consisting of two doublets over the whole temperature range. The value of Debye temperature was estimated from temperature dependence of the isomer shift and the total spectral area and compared with the specific heat capacity data. Neither abnormal behavior of the hyperfine parameters at or near Tc, nor phonon softening were observed., mistake with references corrected

CoxNi1-xFe2O4 (x=0.1, 0.3, 0.5) nanoparticles were synthesized by the PVA Sol-Gel method, and all the samples were found to be single phase spinel by powder X-ray diffraction measurements. High temperature Mossbauer spectra were recorded by a Mossbauer spectrometer. Temperature dependence of hyperfine magnetic fields of two magnetic sextets indicates a "two Neel temperatures" phenomenon in Co0.3Ni0.7Fe2O4 and Co0.5Ni0.5Fe2O4, which has been further demonstrated by the magnetic thermo-gravimetric analysis (MTGA). © 2015 Elsevier B.V. All rights reserved.

This paper investigates the high permeability and high resonance frequency characteristics of carbonyl-iron particle composites at microwave range. It finds that the key factor to keep both high microwave absorbing characteristics is the planar anisotropy. The effective permeability of planar anisotropy carbonyl-iron particles/nonmagnetic matrix composition in high frequency is measured and calculated. In contrast to the sphere shaped particles with no planar anisotropy, the permeability and resonance frequency of flake particles are greatly enhanced by introducing the planar anisotropy, and the permeability can be further enhanced by using a rotational orientation method to get higher planar anisotropy. As the use of the planar anisotropy, the flake soft magnetic particles increase the natural resonant frequencies so as to lead the higher real part and the imaginary part of the permeability in a broadband range. The resonance peak of flake particles is simulated by using the combination of the Landau–Lifshitz–Gilbert equation and Bruggeman’s effective medium theory, considering the correction of shape factor. Our theory simulation agrees well with the experimental data.

CoFe2O4/graphene oxide hybrids have been successfully fabricated via a facile one-pot polyol route, followed by chemical conversion into FeCo/graphene hybrids under H2/NH3 atmosphere. These magnetic nanocrystals were uniformly decorated on the entire graphene nanosheets without aggregation. The morphology, chemical composition and crystal structure have been characterized in detail. In particular, FeCo/graphene hybrids show significant improvement in both permeability and permittivity due to the combination of the high magnetocrystalline anisotropy of metallic FeCo and high conductivity of light-weight graphene. This leads to remarkable enhancement in microwave absorption properties. The maximum reflection loss of FeCo/graphene hybrids reaches −40.2 dB at 8.9 GHz with a matching thickness of only 2.5 mm, and the absorption bandwidth with reflection loss exceeding −10 dB is in the 3.4–18 GHz range for the absorber thickness of only 1.5–5 mm. Moreover, the experimental relationship between matching thickness and frequency is found to obey the quarter-wavelength matching model, facilitating the design of FeCo/graphene hybrid film for practical application. The results suggest that the FeCo/graphene hybrids developed here can serve as an ideal candidate for the manufacture of light-weight and high-efficiency microwave-absorbing devices.

Soft magnetic FeCo@C nanoflakes were prepared by a simple anoxic annealing technique. The crystalline structure, morphology, and microstructure were systematically characterized. The frequency-dependent electromagnetic and absorbing properties of the nanoflake paraffin composites were investigated in the 0.1–18 GHz frequency range. The rotational orientation of the composite in an applied magnetic field was performed to make the plane of nanoflakes parallel to each other. The measurement results showed that both the complex permeability and complex permittivity of the FeCo@C composite were enhanced after orientation. The calculated absorption properties showed that the orientation plays an important role in decreasing the absorber thickness and increasing the absorption performance. For the oriented FeCo@C nanoflake paraffin composite, the maximum reflection loss of −48.2 dB at 2.1 mm thickness and the effective absorption with RL < −10 dB from 2.5 to 12 GHz at thickness ranging from 1.5 to 4.0 mm were obtained.

This study explores the improvement of the reflection loss (RL) by controlling the reflected wave from air–absorber interface (AAI) . The reflected wave from AAI increases for a hybrid system consisted of flake-shaped carbonyl iron absorber and FeCo film coating due to the impedance mismatching. Furthermore, a great enhancement of RL is obtained since the advanced destructive interference of the reflected waves from AAI and absorber–metal interface. Our results indicate the possibility of improving the microwave absorption properties by controlling the reflected wave from AAI, which suggests an alternative method to obtain excellent microwave absorption property in any frequency region.

The Fe-based (T91 and RAFM) alloys are considered as the promising candidate structural materials for DEMO and the first fusion power plant, and these two kinds of steels suffered more serious corrosion attack at 450 °C in liquid PbBi metal. So in order to further clarify the applicability of Fe-based structural materials in nuclear facilities, we should study not only the alloys itself but also its corrosion layers; and in order to simplify the discussion and clarify the irradiation effects of the different corrosion layer, we abstract the Fe3O4 (main corrosion layer of Fe-based alloys) to study the structural, micro-mechanical and magnetic properties under 2.03 GeV Kr-ion irradiation. The initial crystallographic structure of the Fe3O4 remains unaffected after irradiation at low damage levels, but as the Kr-ion fluence increases and the defects accumulate, the macroscopic magnetic properties (Ms, Hc, etc.) and micro-mechanical properties (nano-hardness and Young’s modulus) are sensitive to high-energy Kr-ion irradiation and exhibit excruciating uniform changing regularities with varying fluences (firstly increases, then decreases). And these magnetism, hardening and softening phenomena can be interpreted very well by the effects related to the stress and defects (the production, accumulation and free) induced by high-energy ions irradiation.

CO(2)Z barium ferrite particles with coated Ag nanoparticles were prepared to increase permittivity. The microwave-absorbing properties of the Ag-coated CO(2)Z particle composite showed that the stronger reflection loss (RL) peak and smaller absorber thickness could be achieved simultaneously compared with the pure CO(2)Z barium ferrite particles with the same permeability but smaller permittivity. This enhanced absorption phenomenon was discussed using quarter-wave length cancellation. The separated electromagnetic wave energy reflected at the air-absorber (AA) interface and absorber-metal plate (AM) interface was achieved by measuring reflection coefficients of the composites without (S11-SHORT) and with (S11-SHORT) a backed metal plate to investigate the RL enhancement. (C) 2014 Elsevier B.V. All rights reserved.