Magnetic nanoparticles based on Fe₃O₄ were prepared by a facile and rapid one-pot solvothermal synthesis using FeCl₃·6H₂O as a source of iron ions, ethylene glycol as a solvent and NH₄Ac, (NH₄)₂CO₃, NH₄HCO₃ or aqueous NH₃ as precipitating and nucleating agents. In contrast to previous reports we reduce the synthesis time to 30 minutes using a pressurized microwave reactor without the requirement of further post-treatments such as calcination. Dramatically reduced synthesis time prevents particle growth via Ostwald ripening thus the obtained particles have dimensions in the range of 20 to 130 nm, they are uniform in shape and exhibit magnetic properties with saturation magnetization ranging from 8 to 76 emu g⁻¹. The suggested method allows simple particle size and crystallinity tuning resulting in improved magnetic properties by changing the synthesis parameters, i.e. temperature and nucleating agents. Moreover, efficiency of conversion of raw material into the product is almost 100%.

In this work, a facile two-step strategy is adopted to construct hierarchical polyaniline/NiCo-layered double hydroxide (PANI/NiCo-LDH) core-shell composite nanofiber networks on carbon cloth (CC). Three-dimensional (3D) porous PANI nanofiber networks are firstly uniformly anchored on CC by in-situ oxidative polymerization, followed by growth of NiCo-LDH nanoflakes on the crosslinked PANI framework via electrochemical deposition. The morphology and electrochemical properties of PANI/NiCo-LDH composites are controlled by the deposition time of LDH. Benefiting from rapid electron transport and ion diffusion, the well-defined PANI/NiCo-LDH hierarchical composite with 200 s deposition of LDH delivers a large capacitance of 1845 F g⁻¹ at 0.5 A g⁻¹ and excellent cycling stability of 82% capacitance retention after 5000 cycles at a very high current density of 10.0 A g⁻¹. Furthermore, an asymmetric supercapacitor (ASC) assembled with PANI/NiCo-LDH as a positive electrode and activated carbon (AC) as a negative electrode exhibits a high capacitance of 147.2 F g⁻¹ in a potential range from 0 to 1.5 V and superior energy density of 46.0 Wh kg⁻¹ at a power density of 351.6 W kg⁻¹.

Problems of the theory of radio absorbers (RAs) involving frequency selective surfaces (FSSs) are considered. A design procedure for these RAs is described that takes into account the multiparameter character of the problem and allows one to determine the optimal characteristics of an FSS that provide the maximal operating bandwidth. RAs for a range of 1-17 GHz are obtained on the basis of polymer composites filled with carbonyl iron and Co₂Z ferrite, into which an FSS in the form of a biperiodic array of thin metal rings is embedded. It is shown that the application of such an FSS allows one to increase the operating frequency bandwidth of a magnetic-type RA by a factor of more than 1.5 virtually almost without increasing the thickness of the absorber. Substantially, several types of FSS-based layered magnetodielectric RAs have been produced by compressing molding technique, including a 3-mm-thick RA with an operating bandwidth of 1.05-2.7 GHz, a 2-mm-thick RA with an operating bandwidth of 1.7-4.4 GHz, and a 1.6-mm-thick RA with an operating bandwidth of 6.7-16.1 GHz.