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Highlights: The frequency and intensity of multi-magnetic resonance are freely regulated by co-doping La3+ and Zr4+ ions. Zr4+ occupation is elaborately modified for promoting the portion of polarization/conduction loss to increase profoundly. The optimized electromagnetic characteristics lead to an ultra-wide bandwidth of 12.5+ GHz around millimeter-wave atmospheric window. The utilization of electromagnetic waves is rapidly advancing into the millimeter-wave frequency range, posing increasingly severe challenges in terms of electromagnetic pollution prevention and radar stealth. However, existing millimeter-wave absorbers are still inadequate in addressing these issues due to their monotonous magnetic resonance pattern. In this work, rare-earth La3+ and non-magnetic Zr4+ ions are simultaneously incorporated into M-type barium ferrite (BaM) to intentionally manipulate the multi-magnetic resonance behavior. By leveraging the contrary impact of La3+ and Zr4+ ions on magnetocrystalline anisotropy field, the restrictive relationship between intensity and frequency of the multi-magnetic resonance is successfully eliminated. The magnetic resonance peak-differentiating and imitating results confirm that significant multi-magnetic resonance phenomenon emerges around 35 GHz due to the reinforced exchange coupling effect between Fe3+ and Fe2+ ions. Additionally, Mössbauer spectra analysis, first-principle calculations, and least square fitting collectively identify that additional La3+ doping leads to a profound rearrangement of Zr4+ occupation and thus makes the portion of polarization/conduction loss increase gradually. As a consequence, the La3+–Zr4+ co-doped BaM achieves an ultra-broad bandwidth of 12.5 + GHz covering from 27.5 to 40 + GHz, which holds remarkable potential for millimeter-wave absorbers around the atmospheric window of 35 GHz. [ABSTRACT FROM AUTHOR]

Rare earth ions are highly effective additives for enhancing the absorption properties of W-type barium ferrites. Unfortunately, the in-deep analysis for specific influences of rare earth doping on the absorption properties of barium ferrites is frequently overlooked. Herein, Nd3+ ions-doped W-type barium ferrites (Ba1−xNdxFe18O29 (x = 0–0.3)) used as high-efficiency microwave absorber in multi-band are successfully synthesized by a sol–gel method. The results intriguingly show that the minimum reflection loss (RLmin) of − 7.5 dB for W-type barium ferrite is greatly decreased to − 19.09 dB by Nd3+ doping content of x = 0.2. Simultaneously, multiple effective reflection loss (RL) peaks were produced at certain thicknesses in Nd3+ ions-doped barium ferrites due to the significantly improved electromagnetic response, enlarging the maximum bandwidth to 5.49 GHz. Furthermore, the internal influencing factors of electromagnetic parameters and microwave absorbing properties are thoroughly discussed, which turns out that the boost permittivity and the multi-resonance permeability exhibit an interesting impact on optimizing the microwave absorption behavior. This work is expected to provide meaningful insights into the internal influence mechanism of rare earth element doping on enhancing microwave absorption performance of W-type barium ferrites. [ABSTRACT FROM AUTHOR]

With extensive use of electronic devices and communication equipment, serious issue of electromagnetic wave pollution needs to be addressed as one of the priorities that demand social efforts. In this work, carbon black (CB)/SiO2 composites were synthesized via facile and reliable route and applied for microwave absorption at high-temperature environment around 673 K. Variations of complex permittivity and microwave absorption performance of composites under X-band of 8.2–12.4 GHz and temperature range of 298–673 K were analyzed in detail. Results showed that complex permittivity improved continuously with the increase in CB content and temperature. By elevating the temperature to 673 K, the composite with 10 wt.% of CB can achieve full coverage of effective absorption (RL <− 10 dB) over X-band with thin thickness of 2.9 mm. Therefore, this new composite material has good application prospect as high-temperature microwave absorber, considering its extraordinary properties and easy preparation. [ABSTRACT FROM AUTHOR]

Multiferroic ceramics with extraordinary susceptibilities coexisting are vitally important for the multi-functionality and integration of electronic devices. However, multiferroic composites, as the most potential candidates, will introduce inevitable interface deficiencies and thus dielectric loss from dissimilar phases. In this study, single-phased ferrite ceramics with considerable magnetic and dielectric performances appearing simultaneously were fabricated by doping target ions in higher valence than that of Fe3+, such as Ti4+, Nb5+ and Zr4+, into BaFe12O19. In terms of charge balance, Fe3+/Fe2+ pair dipoles are produced through the substitution of Fe3+ by high-valenced ions. The electron hopping between Fe3+ and Fe2+ ions results in colossal permittivity. Whilst the single-phased ceramics doped by target ions exhibit low dielectric loss naturally due to the diminishment of interfacial polarization and still maintain typical magnetic properties. This study provides a convenient method to attain practicable materials with both outstanding magnetic and dielectric properties, which may be of interest to integration and multi-functionality of electronic devices. [ABSTRACT FROM AUTHOR]