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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 Co 0.72 Fe 0.28 alloy magnetic absorbents with dispersedly distributed NdCo 5 /LaCo 5 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 RECo 5 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 (RL min) 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. [Display omitted] [ABSTRACT FROM AUTHOR]

• The NiO/Ni foam composites were prepared by in-situ growing NiO particles on the surface of nickel foam using a facile calcination strategy. • The effects of calcination conditions on microwave absorption properties of NiO/Ni composite foams were studied. • At a filler content of 60 wt%, the RL min reaches -39.71 dB, accompanied by an EAB of 5.15 GHz. Light weight is a significant target for the magnetic metal-based electromagnetic wave (EMW) absorbents. Constructing foams with porous structure and low density has been proved to be a feasible way. However, the high conductivity of the metal foam will bring a poor impedance match, which hinders the EMW absorbing property. Herein, we reported a facile one-step calcination strategy for the magnetic metal foams toward improved impedance match. The NiO/Ni foam composites were obtained with NiO particles in situ grown on the surface of foams. Greatly enhanced EMW absorption performance was obtained with minimum reflection loss (RL min) of −39.71 dB at a frequency of 13.6 GHz and a thickness of 2.0 mm. Meanwhile, the effective absorption bandwidth (EAB) could reach 5.15 GHz. The introduction of surface NiO weakens the conductivity of pure metals and the abundant pore structures of NiO as well as the inherent three-dimensional (3D) networks of metal foams further promote the multiple reflections and scattering of the EMWs. Consequently, this work provides a feasible and convenient way for the massive production of magnetic metal foams as excellent EMW absorbents. [ABSTRACT FROM AUTHOR]

Magnetic materials with highly efficient microwave absorption properties, crucial for dealing with the advanced wireless communications and radar detections, have been garnering significant attentions. Rare-earth transition-metal compounds were researched as the potential candidates but still suffer from the disadvantages of complex powder metallurgy process and low serving frequencies. In this work, the novel magnetic composites consisting of SmCo 5 and Sm 2 Co 17 are developed by a reduction diffusion method. The micromorphology and the binary phase ratios of the SmCo 5 /Sm 2 Co 17 could be easily modulated by simply altering the reactant concentrations. Consequently, an optimum reflection loss of − 50.2 dB and broad absorption bandwidth of 4.95 GHz at a thickness of only 2.0 mm are achieved. The improved microwave absorption properties of the SmCo 5 /Sm 2 Co 17 binary-phase magnetic absorbents can be attributed to their adjustable magnetic phases and the distinctive flaky particle shape, which greatly enhance microwave absorption capabilities. This work demonstrated a feasible reduction diffusion method and proposed a new strategy of designing binary-phase magnetic materials to achieve high microwave absorption properties. • A novel binary-phase Sm-Co composite were first reported by diffusion-reduction method. • Modified flaky microstructures and tunable microwave absorption properties were achieved. • High frequency magnetic loss was enhanced by inducing shape anisotropy. • Minimum RL of − 50.2 dB and EAB of 4.95 GHz were obtained at only 2.0 mm. [ABSTRACT FROM AUTHOR]

Aiming to obtain advanced microwave absorbing materials with high absorption efficiency, broad absorption bandwidth and low density, herein, a novel nanocomposite with irregular hollow nanostructure of Co 9 S 8 @C was successfully prepared via a soft template and annealing method. Due to the shrinkage process of the Co 9 S 8 nanospheres by annealing, Co 9 S 8 cores and carbon shells were easily obtained. Because of the unique microstructure with irregular outer shells and heterogeneous interfaces, improved polarization loss, multiple reflection loss as well as the impedance matching capability was achieved. As a result, greatly enhanced microwave absorption performance with a reflection loss (RL) of − 51.3 dB at 4.12 GHz, and effective absorption bandwidth (RL<−10 dB) of 5.44 GHz at a thickness of only 1.35 mm was obtained, suggesting the unique Co 9 S 8 @C nanocomposite in this work to be an intriguing and promising microwave absorber. [Display omitted] • Co 9 S 8 @C nanocomposites with hollow and core-shell nanostructures were prepared. • Optimal RL of − 51.3 dB was obtained at 4.12 GHz for the Co 9 S 8 @C nanocomposites. • Broad bandwidth of 5.44 GHz was achieved by modulating the carbon content. [ABSTRACT FROM AUTHOR]

• The resonance frequency of BaFe 12 O 19 is effectively shifted to 2–18 GHz by Zr4+-Ni2+ doping. • Greatly enhanced microwave absorption of the ferrites is obtained by sintering in Ar. • The regulated resonance behavior and improved microwave absorption are explained. To achieve excellent microwave absorption properties within the frequency range of 2–18 GHz, Zr4+-Ni2+ co-doped barium ferrites BaFe 12-2x (ZrNi) x O 19 have been synthesized through a sol–gel process and subsequent sintering. Broadened bandwidth of ∼6.9 GHz and strong microwave absorption of −59.3 dB is attained for the ferrite with x = 0.6 and sintering in Ar. The excellent microwave absorption properties are attributed to both the effective shifting of resonance peaks by Zr4+-Ni2+ substitution and the enhanced dielectric loss by generating lattice vacancies through the oxygen-deficient sintering process. This work would be helpful to understand the nature of manipulating the resonance behaviors and further improving the microwave absorption efficiency of traditional ferrite absorbers. [ABSTRACT FROM AUTHOR]

The theoretical data-driven method and experimental diatomic doping strategy have been integrated skillfully to develop high-performance microwave performance in the B/N co-doped carbon/Fe 3 C magnetoelectric system, realizing the customized electromagnetic parameters and the excellent microwave absorption bandwidth of 7.2 GHz. [Display omitted] The electromagnetic (EM) parameters are the key factors to decode the complex microwave absorption properties, including matching thickness, absorption bandwidth and intensity. Numerous works hence have been focused on optimizing EM parameters to reinforce the comprehensive absorption performance, while most of the adopted experimental means still remain in sporadic and random attempts. In this work, the data-driven approach is first employed to forecast that a fierce frequency-dispersion of permittivity is necessary for the broad absorption, and the appropriate magnetic component can mitigate this elusive trend of required permittivity. Oriented by the simulated results, the B/N diatomic doped C/Fe 3 C magnetoelectric composites are successfully constructed, aiming at the precise regulation of electronic properties to achieve these specially customized EM parameters by forming multi-polarization resonances. The results demonstrate that the introduction of N defects and B defects could enrich the types of dipole pairs (C N, C-B, C N B, vacancy, etc.) and thus activate multi-polarization behavior. The charge density differences calculated by the first-principle further demonstrate that the occupation of B for C bonded with Pyridinic-N and Pyrrolic-N contributes to intense polarization behaviors over the lower frequency range. As a result, excellent microwave absorption properties can be finally achieved with an effective absorbing bandwidth reaching 7.2 GHz at 2.1 mm, implying that the joint use of data-driven and doping engineering strategies to customize frequency dispersion characteristics provides precious guidelines for boosting microwave absorption performance. [ABSTRACT FROM AUTHOR]

Abstract To achieve excellent microwave absorption properties around atmospheric window of 35 GHz, Ti4+ ions doped barium ferrites BaFe x TiO 19 with Fe/Ba ratio of 11:1–9.5:1 are synthesized by a sol-gel progress. Broad bandwidth of ∼11 GHz and strong microwave absorption of ∼ -37 dB are attained around 35 GHz with thickness of ∼2.8 mm and Fe/Ba ratio of 10:1–9.5:1. The correlation between Fe/Ba ratio and the multi-resonance behavior of BaFe x TiO 19 is fully revealed. It is found that the resonance peak shifts to lower range and the peak ascribed to exchange coupling between Fe2+ and Fe3+ enhances gradually with Fe/Ba ratio decreasing from 11:1 to 10:1–9.5:1. The impedance matching principle calculations combined with quarter-wavelength theory give the required permeability of the barium ferrites for considerable microwave absorption properties, and fully confirm the experimental results. This study would be beneficial to both understanding the nature of the multiple resonance behavior impacting on the microwave absorption properties and designing the future high-efficiency microwave absorbers. Graphical abstract Image 1 Highlights • The control of Fe/Ba ratio on multi-resonance behavior of BaFe x TiO 19 is revealed. • The required permeability for excellent absorption properties is vividly displayed. • BaFe x TiO 19 (x = 10:1–9.5:1) exhibits both broad bandwidth and strong RL around 35 GHz. [ABSTRACT FROM AUTHOR]

Urgent demands to reduce the harmful electromagnetic radiation and improve weapons survivability made it necessary to develop high-efficiency microwave absorption materials, especially those operating in frequency range of 2–12 GHz. In this work, Fe 3 O 4 /Ag composites were synthesized by one-step hydrothermal method. Microwave absorbing performance can be flexibly tuned by varying Fe 3 O 4 /Ag molar ratio from 2:1, 3:1, to 4:1. An increase in Fe 3 O 4 /Ag molar ratio would lead to an enhanced permeability over the frequency region of 4–12 GHz. Meanwhile, real part of permittivity remains almost unchanged whereas the imaginary part drastically decreases, making impedance matching and attenuation capacity increase dramatically. In this way, splendid microwave absorption performance with broad absorption bandwidth within a range of 4.88–9.76 GHz and minimum reflection loss of −63.2 dB could be achieved at composite thickness of 3.6 mm. [ABSTRACT FROM AUTHOR]

To gain broad microwave absorption bandwidth over 2–18 GHz, hard/soft magnetic composites Ba(Zr–Ni) 0.6 Fe 10 · 8 O 19 /Fe 3 O 4 have been synthesized in this work. The results show that the raising heat treatment temperature would cause more Fe 3 O 4 particles attach to Ba(Zr–Ni) 0.6 Fe 10 · 8 O 19 particles, increasing the number of interfaces between Ba(Zr–Ni) 0.6 Fe 10 · 8 O 19 and Fe 3 O 4 to enhance the hard/soft exchange coupling effect. Finally, the sample heat treated at 400 °C possesses the widest magnetic loss range (μ″>0.2) of 12.4 GHz, which contributes to a broad effective absorbing bandwidth of 6.68 GHz at 1.9 mm. The performance is superior than most of the state-of-the-art microwave absorbers. [ABSTRACT FROM AUTHOR]

In this study, to effectively broaden the absorption bandwidth of M-type barium ferrite (BaM) in frequency range 2–18 GHz, Zr4+-Ni2+ ions gradient-substituted BaM samples were synthesized via secondary heating the mixtures of homogeneous-substituted Ba(ZrNi) 0.6 Fe 10.8 O 19 and Ba(ZrNi) 0.7 Fe 10.6 O 19. Effects of primary and secondary heat treatment on electromagnetic (EM) parameters of gradient-substituted BaM were investigated in detail. Permittivity values of samples are mainly controlled by primary heat treatment, enhancing with increasing temperature, whereas magnetic loss range is enlarged by improving primary and secondary heat treatment. As a result, the frequency range with μ" value > 0.3 reaches to 6.84 GHz for the sample "1400–1200 °C". Enhanced dielectric and magnetic losses contribute high attenuation constant over wide frequency range, finally resulting in broad absorption bandwidth of 6.24 GHz at matching thickness of 2.8 mm. The bandwidth improved by 21% and 44% compared to that of original Ba(ZrNi) 0.6 Fe 10.8 O 19 and Ba(ZrNi) 0.7 Fe 10.6 O 19 , respectively. This study sheds new light on the preparation of broadband absorbing materials. [ABSTRACT FROM AUTHOR]

Abstract In this work, a series of the single-phased Zr4+-doped Fe 3 O 4 (Fe 3-x Zr x O 4 , x = 0–0.5) powders with spherical morphology were synthesized by one-step hydrothermal method. The results show that the lattice parameter 'a' decreases initially from 0.8410 nm (x = 0) to 0.8299 nm (x = 0.3) and then increases to 0.8338 nm (x = 0.5) whilst Fe2+ concentration improves and crystallinity reduces gradually from x = 0 to x = 0.5 in Fe 3-x Zr x O 4. The ε′ reduces largely from 9.36 to 8.34 without doping to 6.8–5.05 with x = 0.5, and the ε′′ increases from ∼0.70 to ∼1.14 over 2–12 GHz while the relaxation phenomenon occurring above 12 GHz of the undoped-sample disappears with the addition of Zr4+ ions. Meanwhile, the permeability decreases only a little with the increment of x, which leads to the impedance matching of Fe 3-x Zr x O 4 progressively increase while attenuation ability continuously decrease. Finally, contributed by coordinated impedance matching and attenuation performances, Fe 3-x Zr x O 4 with x = 0.1 exhibits strong reflection loss of −41.56 dB and broad bandwidth of 5.57 GHz with double absorption peak at the thickness of 5.75 mm. This study provides a valid avenue to develop high-efficiency absorbing materials by coordinating impedance matching and attenuation performances. Graphical abstract Image 1 Highlights • Single-phased Zr4+-doped Fe 3 O 4 powders were prepared by hydrothermal method. • The substitution sites of Zr4+ ions for Fe ions in Fe 3 O 4 were revealed in detail. • Impedance matching coordinated well with attenuation for Fe 3-x Zr x O 4 (x = 0.1). • Fe 3-x Zr x O 4 (x = 0.1) exhibits strong RL of −41.6 dB and broad bandwidth of 5.6 GHz. [ABSTRACT FROM AUTHOR]

Highlights • Nb5+ doped barium ferrite was sintered at 1400 °C in Ar, N 2 for the first time. • Permittivity is greatly enhanced under millimeter-wave by sintering in N 2 atmosphere. • RL of −37 dB and broad bandwidth of 12 GHz are achieved at thin thickness of 0.55 mm. Abstract To enhance the millimeter-wave absorption properties around atmospheric window of 35 GHz, Nb5+ doped barium ferrite precursors are sintered at 1400 °C for 3 h in air, Ar, N 2 respectively. The magnetic loss region covers 30 ∼ 40 GHz in the sample sintered in air and extends to 26.5 ∼ 40 GHz in the sample sintered in N 2. The ε ′ and ε ″ vary from ∼5 to ∼0.4 by sintering in air to ∼10 and ∼0.3 by sintering in Ar, and to ∼13 and ∼2.0 in N 2. Ultimately, contributed by enhanced permittivity and extended magnetic-loss region, the sample sintered in N 2 exhibits impressive millimeter-wave absorption properties around 35 GHz with broad bandwidth more than 12 GHz and maximum reflectivity of −37 dB under thin thickness of 0.55 mm. [ABSTRACT FROM AUTHOR]

Despite significant advantages in terms of portability and cost, near-infrared (NIR) gas sensing still remains a great challenge due to its relatively weak overtone absorption from the fundamental vibrational bond absorption at the mid-IR frequency. In this paper, we demonstrated ultra-sensitive NIR gas sensing for carbon dioxide (CO 2 ) at 1.57 μm wavelength through nanoporous Cu-BTC (BTC = benzene-1,3,5-tricarboxylate) metal-organic framework (MOF) coated single-mode optical fiber. For the first time, we obtained high-resolution NIR spectroscopy of CO 2 sorbed in MOF without seeing any rotational side band, indicating that the tightly confined gas molecules in the MOF pores do not have any freedom of rotation. Real-time measurement of the mixed gas flow of CO 2 and Ar showed different response time depending on the concentration of CO 2 , which is attributed to the complex sorption mechanism of CO 2 in Cu-BTC MOF. Most importantly, we realized ultra-low detection limit of CO 2 (<20 ppm) with only 5 cm long Cu-BTC MOF thin film coated on single-mode optical fibers. [ABSTRACT FROM AUTHOR]

Broad bandwidth is achieved in oriented flaky Fe-Co-Nd via generating additional dielectric loss peaks. Simultaneously, morphology anisotropy leads to tunable absorption performance at 6–15 GHz by adjustment of angle between the particles and EM waves. • Oriented flaky Fe-Co-Nd is successfully prepared by a magnetic rotation strategy. • Percentage bandwidth is broadened from 31% to 56–66% by orientation. • Absorption range can be tuned within 6–15 GHz under thin thickness of 1.5 mm. To achieve a broad bandwidth microwave absorption at a thin thickness, oriented flakey FeCoNd (F-FCN) is proposed in this work. The orientation leads to the enhancement of permeability and diminishment of permittivity. More importantly, the aligned distribution enhances interface polarization and dipole polarization at specific frequencies and hence generate resonance peaks in permittivity spectra. As a result, percentage bandwidth is gravely broadened from 31% to 56–66% after orientation with thin thickness of 1.5 mm, which is superior than most of the similar absorbers. In addition, because of the morphology anisotropy induced by orientation distribution, microwave absorption performance can be effectively tuned within the range of 6–15 GHz which covers nearly 80% of the C-Ku bands at 1.5 mm by adjusting the angle between the absorber coating surface and the oriented flakey FeCoNd particles. [ABSTRACT FROM AUTHOR]

Excellent absorption properties are achieved in (FeCo) 100−x Nd x via tuning the phase constitution and crystallinity. Moreover, the RL of samples covers almost full test band and has preferable correspondence with radar bands (S, C, X, Ku) with a restricted coating thickness. • Fe-Co-Nd absorbers with significant decreased |μ r |·|ε r | are successfully prepared. • The controls of phase constitution and crystallinity on EM properties are revealed. • Broad bandwidth of 6.92 + GHz and RL min of −52.5 dB under 1.45 mm can be achieved. • The qualified RL of S2-S5 covers almost the whole range of 2–18 GHz under 2 mm. To achieve superior microwave absorption and ultra-wide regulation frequency range under a restricted thickness, (FeCo) 100−x Nd x (0 ≤ x ≤ 15) powders were prepared through a single roller melt spinning technique. The introduction of Nd decreases the crystallinity of FeCo phase and promotes the formation of secondary Nd 2 (FeCo) 17 phase, which results in apparent reduction of electromagnetic (EM) parameters. The correlations between EM parameters and final microwave absorption properties are discussed in detail. It is found that the suppressed EM parameters modifies the coordination between impedance matching and attenuation performance, ultimately leading to superior microwave absorption performance with broad bandwidth of 6.92 + GHz and RL min of −52.5 dB under thickness of only 1.45 mm. Moreover, due to the dramatic decline of |μ r |·|ε r | values, the qualified RL of the samples covers almost all the test frequency (2–18 GHz) with thin thickness of 2 mm, showing great practical value in full-spectrum microwave absorption area with a restricted coating thickness. [ABSTRACT FROM AUTHOR]

In this work, Fe 3 O 4 /Cu composites with both nanorods and nanospheres have been constructed by one-step hydrothermal method. With the decrease of Fe/Cu molar ratio, Cu2+ ions enter into the lattice of Fe 3 O 4 and substituted for Fe2+/Fe3+ ions firstly, then part of Cu2+ ions start to be reduced to Cu metal at molar ratio of 27:3. The samples only possess nanospheres with molar ratio of 30:0–27:3, while nanorods emerge and particle size of nanospheres reduces simultaneously with the ratio reaching to 25:5–23:7. Finally, contributed by nature resonance loss of Fe 3 O 4 , high conductivity loss of Cu, interfacial polarization between heterogeneous Fe 3 O 4 and Cu as well as the coexistence of nanospheres and nanorods, the composite with Fe/Cu molar ratio of 25:5 shows RL min of −53.43 dB and broad bandwidth (RL < −10 dB) of 5.84 GHz under the thin thickness of 1.9 mm over 2–18 GHz, which is superior than most of the existed Fe 3 O 4 -based microwave absorbers. Image 1 • Fe 3 O 4 /Cu composites with both nanorods and nanospheres were attained successfully. • S4 exhibits RL min of −53.43 dB and broad bandwidth of 5.84 GHz under only 1.9 mm. • Multiple absorption mechanisms were fully explored for the excellent property. [ABSTRACT FROM AUTHOR]

• Fe-Co-Ni alloys with improved crystallinity and flake-like particles are prepared. • The mechanisms for enhanced EM parameters in Ni-substituted samples are revealed. • (FeCo) 95 Ni 5 exhibits broad bandwidth of 7.64 GHz under thin thickness of 1.4 mm. The microwave absorption properties of (FeCo) 100−x Ni x (0 ≤ x ≤ 15) samples were investigated in this study, which were made by a simple single roller melt spinning technique. It was found that the introduction of Ni into FeCo can significantly enhance the crystallinity and flake-like particles in the samples. The complex permeability and permittivity increase gradually with increment of Ni content. Notably, a broad peak emerges in the imagine part of permeability at 4–16 GHz for the Ni-substituted samples which covers almost all the tested frequency region. The contributions of microstructure and morphology to the increased electromagnetic parameters are explored detailedly in this work. Moreover, attenuation ability enhances while impedance matching performance deteriorate gradually with Ni content improving. It is interestingly to find that the sample with x = 5 exhibits the maximum qualified bandwidth (≤−10 dB) of 7.64 GHz with a thin thickness of only 1.4 mm eventually, which is superior to many reported microwave absorbing materials. [ABSTRACT FROM AUTHOR]