Search

Graphite nanoplatelets (GNPs)-the segregated ultra-high molecular weight polyethylene (UHMWPE)-based composites with hybrid filler-decorated with Fe 3 O 4 were developed. Using X-ray diffraction and scanning electron microscopy, it was shown that the decorated component has the shape of separate granules, or their clusters were distributed evenly over the GNPs surface. The individual Fe 3 O 4 nanoparticles are predominantly rounded, with diameters of approximately 20-60 nm. The use of GNPs/Fe 3 O 4 as a filler leads to significant decreases in the percolation limit φc, 0.97 vol% vs. 0.56 vol% for GNPs/UHMWPE- and (GNPs/Fe 3 O 4 )/UHMWPE segregated composite material (SCM), respectively. Modification of the GNP surface with Fe 3 O 4 leads to an essential improvement in the electromagnetic interference shielding due to enhanced microwave absorption in the 26-37 GHz frequency range in its turn by abundant surface functional groups and lattice defects of GNPs/Fe 3 O 4 nanoparticles.

The microwave properties of epoxy composites filled with 30 wt.% of BaFe 12- x Ga x O 19 (0.1 ≤ x ≤ 1.2) and with 1 wt.% of multi-walled carbon nanotubes (CNTs) were investigated in the frequency range 36-55 GHz. A sufficient increase in the microwave shielding efficiency was found for ternary 1 wt.%CNT/30 wt.% BaFe 12- x Ga x O 19 /epoxy composites compared with binary 1% CNT/epoxy and 30 wt.% BaFe 12- x Ga x O 19 /epoxy due to the complementary contributions of dielectric and magnetic losses. Thus, the addition of only 1 wt.% of CNTs along with 30 wt.% of barium hexaferrite into epoxy resin increased the frequency range where electromagnetic radiation is intensely attenuated. A correlation between the cation Ga 3+ concentration in the BaFe 12- x Ga x O 19 filler and amplitude-frequency characteristics of the natural ferromagnetic resonance (NFMR) in 1 wt.%CNT/30 wt.% BaFe 12- x Ga x O 19 /epoxy composites was determined. Higher values of the resonance frequency fres (51.8-52.4 GHz) and weaker dependence of fres on the Ga 3+ concentration were observed compared with pressed polycrystalline BaFe 12- x Ga x O 19 (fres = 49.6-50.4 GHz). An increase in the NFMR amplitude on the applied magnetic field for both random and aligned 1 wt.% CNT/30 wt.% BaFe 12- x Ga x O 19 /epoxy composites was found. The frequency of NFMR was approximately constant in the range of the applied magnetic field, H = 0-5 kOe, for the random 1 wt.% CNT/30 wt.% BaFe 12- x Ga x O 19 /epoxy composite, and it slightly increased for the aligned 1 wt.% CNT/30 wt.% BaFe 12- x Ga x O 19 /epoxy composite.

The paper describes preparation features of functional composites based on ferrites, such as "Ba(Fe 1 - x Ga x ) 12 O 19 /epoxy," and the results of studying their systems; namely, the correlation between structure, magnetic properties and electromagnetic absorption characteristics. We demonstrated the strong mutual influence of the chemical compositions of magnetic fillers (Ba(Fe 1 - x Ga x ) 12 O 19 0.01 < x < 0.1 solid solutions), and the main magnetic (coercivity, magnetization, anisotropy field and the first anisotropy constant) and microwave (resonant frequency and amplitude) characteristics of functional composites with 30 wt.% of hexaferrite. The paper presents a correlation between the chemical compositions of composites and amplitude-frequency characteristics. Increase of Ga-content from x = 0 to 0.1 in Ba(Fe 1 - x Ga x ) 12 O 19 /epoxy composites leads to increase of the resonant frequency from 51 to 54 GHz and absorption amplitude from -1.5 to -10.5 dB/mm. The ability to control the electromagnetic properties in these types of composites opens great prospects for their practical applications due to high absorption efficiency, and lower cost in comparison with pure ceramics oxides., Competing Interests: The authors declare no conflict of interest.

BaFe 12-x Ga x O 19 (x ≤ 1.2) hexaferrites were synthesized via the usual ceramic technology. It has been established that with an increase in x, the unit cell and magnetic parameters monotonically decrease. The frequency of natural ferromagnetic resonance firstly decreases from 49.6 GHz down to 49.1 GHz when x = 0.6, and then it increases up to 50.5 GHz. The line width monotonically increases from 3.5 GHz up to 5 GHz. The peak amplitude of the resonant curve changes slightly with the exception of when x = 0.9, when it reaches -16 dB. The 1.3 GHz kOe -1 frequency shift in the bias field is more intensive for small values, when x = 0.3. The decreasing values of the magnetic parameters are a result of the dilution of Fe 3+ -O 2- -Fe 3+ superexchange interactions. The behavior of the amplitude-frequency characteristics is largely determined through the reduction of uniaxial exchange anisotropy. The prospects of Ga-substituted hexaferrites acting as a material that effectively absorbs the high-frequency electromagnetic radiation are shown.