Crystal structure and electromagnetic responses of tetragonal GdAlGe

The ternary rare-earth aluminum germanide GdAlGe with tetragonal structure is systematically studied by x-ray diffraction,magnetic and electric measurements.The magnetic and electric properties of GdAlGe are strongly related to its special magnetic structure formed by magnetic Gd3 isosceles triangles△s.The GdAlGe orders ferromagnetically at 21 K due to the exchanging interaction of Gd3△↑-△↑Gd3.The mechanism of magnetic transport originates from the slip scattering induced by Stoner spin fluctuation in the magnetic ordering region and the spin wave scattering induced by the thermal photon excitation and phonon scattering in the paramagnetic region.The positive magnetoresistance is observed in GdAlGe,which might be due to the disordered magnetic scatter induced by magnetic anisotropy in GdAlGe.

The electromagnetic response of composition-regulated honeycomb structural materials used for broadband microwave absorption

The undesirable absorption bandwidth is the main limitation for the application of microwave absorbing materials.Noting that the design of structure and composition of absorbing coating allows it to obtain a satisfying absorption bandwidth and to avoid weight increasing,honeycomb and its sandwich structures coated by various absorbant have been developed and measured using an arch measurement system over2-18 GHz.To further understand the absorption mechanisms of honeycomb structural materials,simulation based on finite element method and transmission line theory is performed to analyze the different responses to the applied microwave between honeycomb structural materials and uniform-medium slab materials.The proper composition design allows control over the microwave loss mechanisms,which optimize the coating to possess both of the dielectric and magnetic advantages.For the honeycomb structural materials,the magnetic resonation is found for the first time,which is resulting from the periodic honeycomb walls on both sides of the dielectric cavity(consisting of the aramid paper interlayer and vacuum hexagonal prisms).In addition,the conversion of structure from solid to honeycomb brings about changes in impedance,propagating path,effective wavelength,effective attenuation area,microwave phases,and inductive coupling effect,etc.,which result in a better microwave absorbing performance.The honeycomb sandwich structure coated by CIP/CB/EP with the weight ratio of 4:0.03:1 shows the absorption bandwidth of~9.8 GHz for reflection loss(RL)lower than-10 dB which covers part of the S and C bands and almost the whole X and Ku bands.

Morphology-controlled CoNi/C hybrids with bifunctions of efficient anti-corrosion and microwave absorption

Till now,fewer literatures have investigated the corrosion resistance of microwave absorbers,especially mental@C/carbon matrix derived from MOF composites,although it is known that carbon shells possess a protective effect.Herein,three kinds of morphology-controlled CoNi/C-N doped architectures were suc-cessfully fabricated via a sequence of processing,namely coprecipitation for ZIF-67,subsequent Ni^(2+) ex-change and ultimate carbonization.Apart from composition characterization,the effects of microstructure tailoring and temperature controlling on electromagnetic response as well as attenuation performance were revealed,where dodecahedron-shaped composites possessed the highest permittivity.By contrast,rod-shaped composites(CoNi/C-r-550 and CoNi/C-r-700)were endowed with superior comprehensive ab-sorption properties,e.g.,RL_(min):-49.8 dB and-64.0 dB;EAB:5.7 GHz and 4.8 GHz,respectively.Besides,samples CoNi/C-d-700 and CoNi/C-r-700 present higher corrosion potential(E_(corr))and lower corrosion current(I corr).Hence,these corrosion-resistant microwave absorbers with outstanding absorption stabil-ity,wetting effect as well as environmental adaptability,can be used as a candidate/raw material for intelligent devices.