Magnetic Loss Research Articles

Enhancement of coercivity and thermal stability for Nd-Fe-B sintered magnets by diffusing Dy-Co-M (M=Cu, Al) alloys

Commercial N52 sintered NdFeB magnets were processed by grain boundary diffusion (GBD) with Dy-Co-M (M=Cu, Al) alloys. The coercivity of magnets greatly increase to 17.62 and 18.83 kOe respectively when diffusing Dy58Co25Cu17 and Dy58Co25Al17 alloys, which are obviously higher than that of Dy58Co42 GBD-treated magnet with 16.64 kOe. Further thermal stability studies indicate that the thermal stability of Dy58Co25Cu17 and Dy58Co25Al17 GBD-treated magnets is further improved compared to the Dy58Co42 GBD-treated magnet. The results show that the temperature coefficients of remanence (20–120 °C) are reduced from –0.148%/°C to –0.134%/°C and –0.132%/°C by Dy58Co25Cu17 and Dy58Co25Al17 GBD-treatment, respectively. Besides, the irreversible magnetic flux losses (120 °C) for Dy58Co25Cu17 and Dy58Co25Al17 diffusion magnets are 4.76% and 2.79%, respectively. Microstructural analyses demonstrate that the presence of Cu and Al elements reduces the excessive accumulation of Dy and Co on the surface in the diffusion magnets and improves the diffusion depth and utilization of Dy and Co. Furthermore, the flow of Co from the triple junction phase to the thin grain boundary phase is promoted, which contributes to the uniform distribution of Co. In addition, the dynamic evolution of the magnetic domain structure during the temperature rise process was studied. This work provides insight into the preparation of high-performance and high-thermal stability magnets.

0.16BaFeO3-0.84MgFe2O4 hexa-spinel composited ferrites with enhanced magneto-dielectric properties for miniaturized high-frequency antennas

we deeply dived multi-phase-based 0.16BaFeO3-0.84MgFe2O4 ferrite for VHF antennas. The structural and magneto-dielectric properties synthesized at various temperatures (1100 °C, 1125 °C, 1150 °C and 1175 °C) were investigated. The results demonstrated the coexistence of hexagonal and cubic spinel phases. Microstructure analysis indicated higher temperature induced lager grain size and denser structure. Meanwhile, both the saturation magnetization (from 28 to 25 emu/g) and coercivity (19–5 Oe) decreased. In addition, real permeability (μ′) and permittivity (ε′) arose at higher temperature, promising equivalent permeability and permittivity. What's more, relatively low magnetic and dielectric losses (tanδμ ∼10−2 to 10−3 and tanδε ∼10−3 to 10−4) promote low energy loss. Finally, a miniaturized antenna with relative bandwidth of 14.6 %, peak gain of 0.98 dB, and radiation efficiency of 74.6 % was simulated based on the processed ferrites. In conclusion, the presented investigation greatly improves the magneto-dielectric response, which paves the way to realize high performance in VHF antenna application.

Construction of chiral magnetic structure with enhancement in magnetic coupling for efficient Low-Frequency microwave absorption

Construction of chiral magnetic structure is considered as a promising strategy to achieve efficient low frequency microwave absorption. However, it is not clear that how the magnetic loss is enhanced by the chiral morphology. Herein, a novel chiral magnetic structure containing FeCo2O4-FeCo nanosheets has been constructed by using helical carbon nanocoils (CNCs) as the chiral template. For comparison, the FeCo2O4-FeCo nanosheets are also combined with the linear carbon nanofibers (CNFs). The enhanced magnetic coupling between FeCo2O4-FeCo nanosheets and the magnetic anisotropy induced by the chiral structure are confirmed by the off-axis electron holography and the micro-magnetic simulation. Due to the synergistic effect between chirality, magnetism, and dielectricity, the chiral magnetic structure exhibits superior microwave absorption performance than the linear one with a wide effective bandwidth of 7.1 GHz at an ultra-low filling ratio of 8 %. Meanwhile, the minimum RL value of −60.7 dB is achieved at low frequency (6 GHz). This study provides further evidence of the special mechanisms of the chiral structure for microwave absorption.

Magnetization of Ferromanganese Crusts: Geochemical and Magnetic Insights From Rio Grande Rise and Tropic Seamount

AbstractFerromanganese (FeMn) crusts are Fe and Mn oxides that typically form on deep‐sea elevations by deposition of colloids from seawater. These mineral deposits are considered a source of critical metals and rare earth elements. Besides their potential economic value, FeMn crusts are extremely relevant in ocean science, since their very slow growth rates result in long‐term paleoenvironmental and paleoceanographic records. In this study, we applied geochemical, mineralogical, and magnetic analyses to unravel paleoenvironmental changes at two locations on opposite sides of the Atlantic Ocean, the Rio Grande Rise in the SW Atlantic and the Tropic Seamount in the NE Atlantic. Our results show that the occurrence of amorphous (non‐crystalline) Fe oxyhydroxides and the absence of Fe oxides in hydrogenetic, non‐phosphatized FeMn crusts prevented the development of primary remanent magnetization. In contrast, phosphatized FeMn crusts may have contained a remanent magnetic signal. Phosphatization resulted from increased primary productivity and occurred at different stages during the growth of the FeMn crusts, leading to suboxic conditions and partial dissolution of pre‐existing, remanence‐carrying magnetic minerals. Carbonate Fluorapatite (CFA) accumulation in the phosphatized layers of FeMn crusts replaced Fe and Mn, decreasing their magnetic content. Thus, magnetic variations do not reflect a primary magnetization but rather result from geochemical alterations. The loss of primary magnetization may hamper the use of FeMn deposits for magnetostratigraphic purposes.

Hollow-magnetite/MXene nanohybrids with unique coral-like structure for electromagnetic wave absorption

The novel hollow-magnetite (HFO)/MXene nanohybrids with coral-like structure were successfully prepared via templating and electrostatic self-assembly techniques for electromagnetic (EM) wave adsorption application. The unique coral-like structure of the prepared HFO/MXene hybrids was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). When mass ratio of HFO to MXene is 2:1, the maximum effective absorption bandwidth (EABmax) of HFO/MXene hybrids is able to reach 5.36 GHz. Moreover, when mass ratio of HFO to MXene is 1:1, the minimum reflection loss (RLmin) even achieves −42.48 dB with a thickness of 3.1 mm. The excellent EM absorption performance of HFO/MXene hybrids is mainly due to the ideal impedance matching and synergistic effect of magnetic loss and dielectric loss caused by unique coral-like structure. This work provides unexplored areas in the design of the spatial structure of MXene for microwave absorption.

Biomass-derived carbon heterostructure composites modified with magnetic iron oxide for excellent EMW-absorbing materials

With the gradual spread of satellite navigation, broadcasting, and communication technologies, the problem of electromagnetic pollution in C- and Ku-band has increased. Electromagnetic wave (EMW) absorbing materials can effectively mitigate this problem. Here, we report the design of a biomass carbon heterostructure for the absorption of EMWs. This design takes advantage of the natural fiber mesh structure of the loofah and the voids, veins, and basal tissues surrounding the fibers. The material is then carbonized to create a radar antenna-like structure of fibers and nanosheets. This improves the material's conductive loss. In addition, modification with magnetic iron oxide in loofah sponges improves the impedance matching of the materials, enhances the magnetic loss, and increases the heterogeneous interface. We found that the maximum effective absorption frequency range of the prepared EMW-absorbing materials is 3.80 GHz, which is mainly concentrated in the C-band and Ku-band, and its maximum RLminvalue is −59.20 dB. The material's ability to absorb EMWs was also verified by simulating the radar cross section (RCS). In conclusion, this work develops a green and efficient composite material for absorbing EMWs and provides new design ideas for the development of EMW-absorbing materials.

The preparation and magnetic properties of FeSiCr/MoS2 soft magnetic composites

Two-dimensional layered material MoS2 was used as a high-resistance insulating material and coated on FeSiCr magnetic powder, and FeSiCr/MoS2 composites with low loss and high permeability were successfully prepared. The morphology and magnetic properties of FeSiCr/MoS2 composites were analyzed by XRD, SEM and B-H analyzer. The results show that although the addition of MoS2 will dilute the magnetic properties of FeSiCr, it still has high permeability and obviously reduces the magnetic loss of FeSiCr powder. At the same time, the addition of MoS2 also improves the frequency stability and quality factor of the composite powder cores. Especially, when the MoS2 content is 1.5 wt%, FeSiCr/MoS2 composites show the best magnetic properties after annealing at 500 °C. with a loss of 330 mW cm−3 and permeability of 66.75 (B m = 20 mT and f = 1000 kHz). It can be seen that the MoS2 coating has a good effect on reducing the magnetic loss of powder core, which significantly improves the possibility of application of SMCs at high frequency.

Physical signatures of fermion-coupled axion dark matter

In the presence of axion dark matter, fermion spins experience an “axion wind” torque and an “axioelectric” force. We investigate new experimental probes of these effects and find that magnetized analogs of multilayer dielectric haloscopes can explore orders of magnitude of new parameter space for the axion-electron coupling. We also revisit the calculation of axion absorption into in-medium excitations, showing that axioelectric absorption is screened in spin-polarized targets, and axion wind absorption can be characterized in terms of a magnetic energy loss function. Finally, our detailed theoretical treatment allows us to critically examine recent claims in the literature. We find that axioelectric corrections to electronic energy levels are smaller than previously estimated and that the purported electron electric dipole moment due to a constant axion field is entirely spurious.

Research on the Material Characteristics and Loss Calculation Method of Cryogenic Permanent Magnet Motor Stator for LNG Pump

This paper explores the applicability of cryogenic permanent magnet motor stator materials for LNG pumps. First, this study selected four kinds of silicon steel sheets for motor stators tested at room temperature and ultra-low temperature and obtained the magnetization characteristics and loss characteristics of the four silicon steel sheets at room temperature and ultra-low temperature. Then, through a comparative analysis of experimental data, the applicability of silicon steel sheet material in an ultra-low-temperature environment was verified. Finally, the improved methods of the basic iron loss model of silicon steel sheets and the basic iron loss model of motors were proposed, and the accuracy and feasibility of the improved models were verified.

Nickel-Fe3O4@Graphene coated lightweight carbonized wood for efficient electromagnetic interference shielding

The miniaturization and integration of electronic equipment promote electromagnetic effect radiation pollution more and more serious. The lightweight, renewable electromagnetic interference (EMI) shielding materials is urgently needed. This study developed a high temperature carbonization, Fe3O4@Graphene impregnation, and electroless Ni technique to construct a carbonized wood composite with strong EMI shielding performance using sustainable natural wood as the raw material. The Fe3O4@Graphene is distributed throughout the carbonized wood to provide the conductivity and magnetism of the reinforced composite material, and provide more interfaces to increase the dielectric loss and magnetic loss, thereby exhibiting excellent EMI shielding performance. The results show that at low thickness (2 mm) and ultra-low density (0.284 g/cm3), the CWN-7 composite exhibits excellent EMI shielding effectiveness of up to 84.2 dB in the whole X-band (8.2–12.4 GHz). At the same time, it has extraordinary compressive strength and good thermal insulation performance. This study offers a different method for creating composite multifunctional electromagnetic shields out of carbonized green wood.

Study on the influence of the degree of the easy-plane orientation on the high-frequency magnetic properties and power loss of SMC in the MHz band

The effects of the degree of the easy-plane orientation on soft magnetic composite (SMC) are studied, utilizing the α-Fe easy-plane soft magnetic composite (α-Fe EPSMC) as the study system. The relationships between the degree of the easy-plane orientation (DEPO) and magnetic properties as well as power loss are studied. It is found that the magnetic properties and the power loss are significantly improved with DEPO increasing. The permeability increases from 22 to 45, the domain wall resonance frequency increases from 22 MHz to 210 MHz, the natural resonance frequency increases from 0.125 GHz to 1.36 GHz, the frequency stability increases from 3 MHz to 100 MHz. The power loss decreases from 6560 kW/m3 to 568 kW/m3 (5 MHz, 8 mT). In addition to the obvious improvement in properties, it is more important to establish relationships between the DEPO and power loss. It is found that the DEPO is inversely proportional to the hysteresis loss and the excess loss. The high DEPO mainly achieves the decrease of hysteresis loss and excess loss by decreasing the angle between the magnetization vector and external magnetic field and increasing domain wall resonance frequency. This study proposes a novel type of SMC (α-Fe EPSMC) with ultra-low power loss and excellent magnetic properties. It is more important that this study provides new ideas and methods for decreasing the power loss of SMC in the MHz band and studying the power loss mechanism of SMC in the MHz band.

Temperature regulated Fe3Si@SiC@carbon core-shell structure with high-performance microwave absorption

Developing high-performance microwave absorbing materials (MAMs) to address the electromagnetic wave pollution is still a huge challenge. Multi-interface core-shell structure with magnetic and dielectric loss components have been attracting extensive attention as MAMs for the enhanced interfacial polarization and impedance matching. In this work, magnetic loss core and dielectric loss bi-shell structure Fe3Si@SiC@C (FSC) composite was synthesized through hydrothermal, self-polymerizing coating and high temperature thermolysis. The thermal treatment temperature has a great effect on the morphology structure and electromagnetic properties of FSC. The results indicated that the FSC exhibited an effective absorption bandwidth (EAB) of 4.24 GHz at a thickness of 1.4 mm, and an EAB of 12.4 GHz with the absorber thickness varied from 1 mm to 3 mm. Furthermore, the microwave attenuation mechanism of the FSC composite were investigated in detail. The integration of magnetic core with multiple dielectric shells provides a design deliberation and reference for further high-performance MAMs fabrication.

Nd-, La-induced precipitate/defect in cobalt-iron magnetic alloy for strong and broadband microwave absorption

Soft magnetic microwave absorbents have merits of sufficient magnetic loss and unique magnetism-frequency response characteristics, yet are limited by the low natural resonance frequencies and simplex loss mechanism. Introducing second phase has been proven to be efficient in evoking structure, magnetism and conductivity changes, but the effects on the microwave absorption is still unbeknown. In this work, the Co0.72Fe0.28 alloy magnetic absorbents with dispersedly distributed NdCo5/LaCo5 nano precipitates were prepared. By fine-tuning the doping ratios of the rare earth (RE) of Nd/La, the coercivity and conductivity show an upward trend with enhanced magnetic and dielectric losses on 2–18 GHz. On one hand, the high magneto-crystalline anisotropic RECo5 phases uplifted the holistic resonance frequency ranges and enhanced the C/X/Ku band attenuations. On the other hand, the as-spawn vacancies, heterogeneous interfaces and dislocations boosted the conductive/polarization losses of the individual magnetic alloys. As a result, the high-frequency performance was significantly improved when ensuring the impressive low-frequency loss. A remarkable minimum reflection loss (RLmin) of −76 dB was achieved in the S band, and the effective absorption bandwidth (EAB) of 7.34 GHz was obtained at only 1.7 mm, covering most of the X/Ku bands. The performance sets it apart as the highest among the reported RE-transitional alloy absorbents so far. Overall, this work provides a feasible way and novel strategy for improving the microwave absorption properties for the traditional metal alloys and their compounds.

Fabrication of FeSiBPCNbCu nanocrystalline soft magnetic powders with high saturation magnetization and low core loss

Fabrication of FeSiBPCNbCu nanocrystalline soft magnetic powders with high saturation magnetization and low core loss

Lightweight carbon foam composites embedded with RGO/SrFe12O19 hybrid: Fabrication, structural and electromagnetic shielding performance in 8.2 to 12.4 GHz

Today's growth of wireless technology has increased the demand for composite materials with absorption-based shielding capabilities and the composites of dielectric and magnetic materials are suitable for producing high shielding effectiveness (SE). The present study establishes a facile way to synthesize carbon foam embedded with strontium ferrite (SrFe12O19) nanoparticles decorated within/ on reduced graphene oxide (RGO) sheets. In this work, polyurathene templete slab is dipped in the homogenous slurry prepared from RGO/SrFe12O19 (RS) hybrid and phenolic resin followed by carbonization to produce the CF/RGO/SrFe12O19 (CRS) composite foam. The synthesized CRS3 nanocomposite foam exhibits maximum shielding effectiveness due to an absorption (SEA) value of 26.6 dB i.e., ∼99.7% attenuation, and absolute specific shielding effectiveness (SSEt) value of 250.70 dBcm2g–1. The high SEA value of synthesized composite carbon foam is obtained because of the synergistic effect of porous morphology, dielectric losses and magnetic losses.

The hollow cubic octahedral structure of Fe3O4 with excellent electromagnetic wave absorption capacity

The unique nanostructure combined with high dielectric and magnetic losses is essential for electromagnetic wave (EMW) attenuation in microwave-absorbing materials (MAM). In this paper, using cubic octahedral Cu2O as a template, we synthesized hollow cubic octahedral Fe(OH)3 at first. After annealing at 450 °C, the hollow cubic octahedral structure Fe3O4 could be obtained. When the filling ratio was 40 %, the minimum reflection loss (RLmin) reached -66.08 dB, and the maximum effective absorption bandwidth (EAB) was 5.38 GHz at a thickness of 1.84 mm, exhibiting improved EMW properties compared with previous works. The hollow cubic octahedral structure of Fe3O4 enhances EMW absorption characteristics, which is attributed to abundant dipole polarization, interface polarization, and good conduction loss. These results indicate that Fe3O4 with the hollow cubic octahedral structure can be used as potential candidates for efficient and broadband EMW absorbers.

Research on electromagnetic wave absorption properties of Portland cement

In order to evaluate the electromagnetic wave absorption properties of Portland Cement, the chemical composition, mineralogical phase of Portland cement were studied by XPS, XRD and Mössbauer, respectively, and electromagnetic parameters were measured. Afterwards, the reflectivity of the hydrated cement were tested.The results showed that Portland cement exhibits some dielectric loss and weak magnetic loss at 1∼18 GHz, due to the unburned carbon and iron oxide. There are three notable theoretical electromagnetic wave absorption peaks, and the greatest absorption reaches 4.38 dB. The minimum reflectivity of hydrated Portland cement reach -17.9 dB, -17.89 dB and -12.67 dB and the bandwidth of -6 dB reach 6.28 GHz,10.74 GHz and 1.85 GHz at the thickness of 5 mm,10 mm, 15 mm, respectively. There are 3,5,7 reflectivity peaks at the thickness of 5 mm,10 mm, and 15 mm, respectively, which matched very well with the calculated interference peaks.

High-performance NiTi-C nanofibers microwave absorbent prepared by electrospinning

Carbon nanofibers embedded with magnetic NiTi nanoparticles have been synthesized using electro-spinning technique, followed by one-step carbonization. By using NiTi-CFs as filler with 7.5%content, the sample achieved a very high effective absorption bandwidth(EAB) of 6.1 GHz (11.4–17.5 GHz)at the thickness of 1.97 mm. The effective absorption coverage of different microwave bands can be achieved by adjusting the thickness of the material. Adjusting the thickness of the material at 1.35 mm to 5 mm can achieve coverage from 3.7 GHz to 18 GHz. The superior properties might be due to the great impedance matching, rich dielectric loss and magnetic loss basis, excellent 1/4 λ space structure. This work presents a facile and promising method to produce high performance microwave absorption materials with thin thickness, light weight and strong absorption, as well as a detailed study of its wave absorbing basis.

UV‐Curable 3D‐Printable Microwave‐Absorbing Material with a Sword‐Sheath Structure Based on Multiwalled Carbon Nanotube/Polypyrrole Nanotube/Fe3O4 Composites

Multiwalled carbon nanotube (MWCNT)/polypyrrole nanotube (PPyNT)/triiron tetraoxide (Fe3O4) composites with a sword‐sheath structure are added to a UV‐curable resin to form a unique highly microwave‐absorbing material with a low absorbent content. Specifically tailored for high‐precision stereolithography three‐dimensional (3D) printers, the low absorbent content ensures an efficient curing and molding of the photosensitive resin. The conducting polymer polypyrrole is coated on the MWCNTs via free‐radical polymerization, forming a sheath structure. The initiator of the free‐radical polymerization, FeCl3, is converted into Fe3O4 and loaded onto the sheath structure. This ternary composite material is uniformly dispersed in the photosensitive resin with interconnected sword‐sheath structures, ensuring a favorable dielectric loss performance even at a low absorbent content. Importantly, the material exhibits both dielectric loss and magnetic loss properties. Using a UV‐cured microwave‐absorbing material with an absorbent content of 0.5 wt%, an electromagnetic loss of −22.5 dB can be achieved with a thickness of 1 mm. This UV‐cured microwave‐absorbing material facilitates the high‐precision 3D printing of microwave structures with various intricate shapes, broadening the application scope of microwave‐absorbing materials.

Assessing nanobody interaction with SARS-CoV-2 Nsp9.

The interaction between SARS-CoV-2 non-structural protein Nsp9 and the nanobody 2NSP90 was investigated by NMR spectroscopy using the paramagnetic perturbation methodology PENELOP (Paramagnetic Equilibrium vs Nonequilibrium magnetization Enhancement or LOss Perturbation). The Nsp9 monomer is an essential component of the replication and transcription complex (RTC) that reproduces the viral gRNA for subsequent propagation. Therefore preventing Nsp9 recruitment in RTC would represent an efficient antiviral strategy that could be applied to different coronaviruses, given the Nsp9 relative invariance. The NMR results were consistent with a previous characterization suggesting a 4:4 Nsp9-to-nanobody stoichiometry with the occurrence of two epitope pairs on each of the Nsp9 units that establish the inter-dimer contacts of Nsp9 tetramer. The oligomerization state of Nsp9 was also analyzed by molecular dynamics simulations and both dimers and tetramers resulted plausible. A different distribution of the mapped epitopes on the tetramer surface with respect to the former 4:4 complex could also be possible, as well as different stoichiometries of the Nsp9-nanobody assemblies such as the 2:2 stoichiometry suggested by the recent crystal structure of the Nsp9 complex with 2NSP23 (PDB ID: 8dqu), a nanobody exhibiting essentially the same affinity as 2NSP90. The experimental NMR evidence, however, ruled out the occurrence in liquid state of the relevant Nsp9 conformational change observed in the same crystal structure.