RESUMO
Designing heterogeneous interfaces and components at the nanoscale is proven effective for optimizing electromagnetic wave absorption and shielding properties, which can achieve desirable dielectric polarization and ferromagnetic resonances. However, it remains a challenge for the precise control of components and microstructures via an efficient synthesis approach. Here, the arc-discharged plasma method is proposed to synthesize core@shell structural high-entropy-alloy@graphite nanocapsules (HEA@C-NPs), in which the HEA nanoparticles are in situ encapsulated within a few layers of graphite through the decomposition of methane. In particular, the HEA cores can be designed via combinations of various transition elements, presenting the optimized interfacial impedance matching. As an example, the FeCoNiTiMn HEA@C-NPs obtain the minimum reflection loss (RLmin ) of -33.4 dB at 7.0 GHz (3.34 mm) and the efficient absorption bandwidth (≤-10 dB) of 5.45 GHz ranging from 12.55 to 18.00 GHz with an absorber thickness of 1.9 mm. The present approach can be extended to other carbon-coated complex components systems for various applications.
RESUMO
Despite the fact that the high conductivity of two-dimensional laminated transition metal carbides/nitrides (MXenes) contributes to the outstanding electromagnetic interference (EMI) shielding by the reflection of electromagnetic waves (EWs), it is difficulty to improve EMI shielding by pursuing higher conductivity due to the limitation of intrinsic properties. Here, we achieve superior EMI shielding by introducing the absorption of EWs in MXenes with micro-sized wrinkles which are induced by abundant Ti vacancies under chemical etching. The shielding effectiveness is up to 107â dB at a thickness of 20â µm. Combining with atomic-scale structure observation and the first-principles calculations, it is concluded that the promotion of EMI shielding originates from the resonant absorption of formed electric dipoles induced by the asymmetrical distribution of charge densities near Ti vacancies. Our results could open a new vista for developing two-dimensional EMI shielding materials.
RESUMO
The crystal structures, magnetic properties and magneto-caloric effects (MCEs) of RE2Ni2In (RE = Pr, Nd, Dy and Ho) compounds were investigated. The results indicate that Pr2Ni2In and Nd2Ni2In compounds have a tetragonal Mo2FeB2-type structure belonging to the P4/mbm space group and undergo a second-order paramagnetic to ferromagnetic (PM to FM) transition at a Curie temperature (TC) of 7.5 and 10.5 K, respectively, whereas Dy2Ni2In and Ho2Ni2In compounds have an orthorhombic Mn2AlB2-type structure belonging to the space group Cmmm and possess a magnetic transition from PM to antiferromagnetic (AFM) at a Néel temperature TN of 19 and 10.5 K together with a first-order field induced metamagnetic transition, respectively. Moreover, an additional magnetic transition at a lower temperature of around 5.5 K is detected for the Ho2Ni2In compound. A considerable reversible magneto-caloric effect is observed accompanying the magnetic phase transition, and the maximum values of the magnetic entropy change (-ΔS) of the present RE2Ni2In series compounds are determined to be 9.3, 11.5, 6.4 and 11.5 J kg-1 K-1 with a magnetic field change (ΔH) of up to 0-5 T for RE = Pr, Nd, Dy and Ho, respectively.
RESUMO
Superparamagnetic FeCo nanochains consisting of assembled â¼25 nm nanoparticles and â¼1 nm gaps are synthesized by facial wet-chemical route and exhibit significant electromagnetic absorption at gigahertz. Both the dielectric and magnetic loss factors present dual-resonance behaviors at 2-18 GHz frequencies, originated from the asymmetric architecture of the cubic FeCo particles that assembled in a one-dimensional chain structure. Theoretical analyses uncover that the origins of the enhancement of electromagnetic losses are ascribed to the high magnetization (228 emu/g) and the ultrathin gaps (â¼1 nm), which enhances the Snoek limit and induces anisotropic dielectric polarizations, consequently constructing a proper electromagnetic match.