Complex permittivity, permeability, and X-band microwave absorption of CaCoTi ferrite composites

Abstract

The effect of Co2+Ti4+ substitution on complex permeability, permittivity, and microwave absorption has been studied for [Ca(CoTi)xFe12−2xO19]96.0[La2O3]4.0 ferrite-epoxy composites, wherein x varies from 0 to 1.0 in steps of 0.2, in the frequency range from 8.0 to 12.4 GHz. The ferrites with x>0 exhibit significant dispersion in complex permittivity (ε′−jε″) with the maximum value of ε″ observed for x equal to 0.2. The dispersion in complex permeability (μ′−jμ″) is not significant. The variations of reflection loss and percentage absorption have been studied as a function of frequency, Co2+Ti4+ content, and thickness of the absorber. A maximum reflection loss of 31.0 dB is obtained for composites with x equal to 0.2 and absorber thickness of 2.5 mm. The experimental values of the matching frequency and the matching thickness agree well with the theoretical values obtained from an impedance-matching solution map.

Flexible microwave absorbers based on barium hexaferrite, carbon black, and nitrile rubber for 2–12 GHz applications

“…80BaF with an anisotropic field H a ¼ 2.79 kOe displays a ferromagnetic resonance f r ¼ cH a at 7.8 GHz, where c ¼ 2.8 MHz/Oe is the gyromagnetic ratio. 38 The observed l 00 as shown in Figure 5(d) is in good agreement with the kind of mechanism of natural magnetic resonance. The ferromagnetic resonance frequency is expected to decrease considerably with increase in volume fraction of BaF filler as H a is inversely proportional to saturation magnetization.…”

“…The conduction in ferrites is attributed to the existence of both ferrous and ferric ions and electron hopping mechanisms. 38 Moreover, when the frequency of electron hopping between Fe 3þ to Fe 2þ ions matches that of microwave frequency, dielectric resonance occurs, which is responsible for the relaxation peak centred at 9.8 GHz as shown in Figure 5(b). There is a minimal increment in the value of dielectric loss at around 3.6 GHz while there is no corresponding decrease in the real part of effective permittivity.…”

A surfactant-free route to synthesize Ba x Sr1−x TiO3 nanoparticles at room temperature, their dielectric and microwave absorption properties

“…The nawow size distribution and uniform morphology of our BST samples are interesting for investigation of their microwave absorption property. The reflection loss (RL) of the BST/paraffin composites was calculated using the transmission line theory [45,46]:…”

Nanoparticle-assisted microwave absorption by single-wall carbon nanotubes

“…Examples of such structures include Ba hexaferrite nanocrystals 10 and micron-size ferrite powders 11,12 in a rubber matrix, Fe-Si-Al alloy flakespolymer composites, 13 and CaCoTi ferrite-epoxy composites. 14 Microwave absorption in these materials is thought to be mainly due to magnetic resonance and interfacial electric polarization. 15,16 Magnetic resonance absorption occurs due to the coupling of the microwave field to the internal magnetic moments and is influenced by the shape of the particles.…”