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The purpose of this study was to evaluate the electromagnetic (EM) properties of hybrid materials made from polypyrrole (PPy) and barium hexaferrite (HF) for possible use in electromagnetic interference (EMI) shielding applications. X-ray diffraction and Fourier-transform infrared spectroscopy methods were used to confirm the presence of PPy and HF phases inside the hybrid structure. A scanning electron microscope analysis revealed that the HF particles were evenly dispersed throughout the PPy structure. The composites’ dielectric and magnetic attributes were evaluated across a spectrum of frequencies, with the highest values observed in the PPy specimen. Adding HF to the PPy matrix altered the dielectric and magnetic properties of the composite, with the percentage of HF in the composite influencing its dominance over these properties. It was determined that a 25% HF content produced the most stable and efficient composite for absorbing EM waves in the X-band. This study demonstrates the potential of conductive polymer composites for EMI shielding applications, with advantages, such as improved EMI shielding, lightweight, flexibility, corrosion resistance, and tailored properties. The novelty lies in optimizing the composition of the PPy/HF composite and the characterization of its EM properties, providing insights into the design of more efficient EMI shielding materials.

In this work, Barium hexaferrite (BaFe12O19) nanoparticles were used for industrial waste water treatment from methylene blue (MB) and congored (CR) dyes. Batch adsorber with mechanical stirring column was used to test various experimental parameters like contact time, initial dye concentration and adsorbent dosage for the removal of these dyes. For the removal of MB and CR dyes using magnetic nanoparticles, the maximum adsorption capacities were 200 and 124.5 mg/g respectively. The maximum removal efficiencies were 90 % for MB removal onto the nanoparticles and 80% for CR removal. In order to analyze the kinetic data, pseudo first and second order kinetic models have been used. For all studied variables and based on correlation coefficient (R) values and graphical presentation, the results confirm that pseudo second order model fits well the experimental data.

Control of ferromagnetism is of critical importance for a variety of proposed spintronic and topological quantum technologies. Inducing long-range ferromagnetic order in ultrathin 2D crystals will provide more functional possibility to combine their unique electronic, optical and mechanical properties to develop new multifunctional coupled applications. Recently discovered intrinsic 2D ferromagnetic crystals such as Cr 2 Ge 2 Te 6 , CrI 3 and Fe 3 GeTe 2 are intrinsically ferromagnetic only below room temperature, mostly far below room temperature (Curie temperature, ~20–207 K). Here we develop a scalable method to prepare freestanding non-van der Waals ultrathin 2D crystals down to mono- and few unit cells (UC) and report unexpected strong, intrinsic, ambient-air-robust, room-temperature ferromagnetism with T C up to ~367 K in freestanding non-van der Waals 2D CrTe crystals. Freestanding 2D CrTe crystals show comparable or better ferromagnetic properties to widely-used Fe, Co, Ni and BaFe 12 O 19 , promising as new platforms for room-temperature intrinsically-ferromagnetic 2D crystals and integrated 2D devices. Van der Waals crystals have recently been shown to exhibit ferromagnetism, however the Curie temperature is typically quite low. Herein, Wu et al succeed in producing mono and few layer crystals of CrTe, a non-van der Waals crystal, and demonstrate strong intrinsic room temperature ferromagnetism.

We report on the electrodynamic properties of the single crystalline lead-substituted M-type barium hexaferrite, Ba0.3Pb0.7Fe12O19, performed in the broad frequency range including radio-frequency, terahertz and sub-terahertz bands, which are particularly important for the development of microelectronic devices. We demonstrate how changing on a molecular level the chemical characteristics (composition, intermolecular interaction, spin-orbital interaction) of lead-substituted M-type hexaferrite influences its radio-frequency and terahertz electrodynamic response. Our results indicate a critical temperature range, 50 K < T < 70 K, where significant changes of the electrodynamic response occur that are interpreted as freezing of dynamical oscillations of bi-pyramidal Fe(2b) ions. In the range 5-300 K, the heat capacity shows no sign of any phase transition and is solely determined by electron and phonon contributions. An anomalous electrodynamic response is detected at 1-2 THz that features a rich set of absorption resonances which are associated with electronic transitions within the fine-structured Fe2+ ground state and are visualized in the spectra due to magnetostriction and electron-phonon interaction. We show that lead substitution of barium in barium hexaferrite, BaFe12O19, leads to the emergence of a pronounced dielectric and magnetic relaxational dynamics at radio-frequencies and that both dynamics have the same characteristic relaxation times, thus evidencing the bi-relaxor-like nature of Ba0.3Pb0.7Fe12O19. We associate the origin of the relaxations as connected with the motion of magnetic domain walls. In order to unveil crucial influence of chemical substitution on electrodynamic characteristics of the compound, we analyze our results on substituted compound in comparison with the data available for pristine barium (BaFe12O19) and pristine lead (PbFe12O19) hexaferrites. The obtained spectroscopic data on the dielectric properties of Ba0.3Pb0.7Fe12O19 provide insight into fundamental phenomena responsible for the absorption mechanisms of the compound and demonstrates that chemical ionic substitution is an effective tool to tune the dielectric properties of the whole family of hexaferrites.

(xCo)-BaFe 12 O 19 nanoparticles, with 0 ≤ x ≤ 0.1 wt%, have been prepared using a chemical co-precipitation method and different calcination temperatures (850 °C, 900 °C and 950 °C). The samples were subjected to structural, optical and magnetic studies. X-ray powder diffraction showed the hexagonal crystal structure of (xCo)-BaFe 12 O 19 , and the more convenient temperature for the formation of this phase was 950 °C. Transmission electron microscope was used for investigating the morphology as well as the average particle size of the samples. It was found that the average size of all samples ranges between 65 and 90 nm. The energy band gap E g was determined using UV–Vis spectroscopy. It was noticed that the values of E g decreased with the addition of cobalt and the increase in the calcination temperature. The M–H curve obtained from vibrating sample magnetometer has been used to study the magnetic behavior. The anisotropy field ( H a ), the saturation magnetization ( σ s ), the effective crystalline anisotropy constant ( K eff ), the remanent magnetization ( σ r ) and squareness ratio ( S ) for each sample were calculated. The maximum value of coercivity (5087Oe) was found for x  = 0 wt% at T  = 950 °C which is suitable for magnetic applications, such as the recording equipment and permanent magnets.

Ferrites count among the most functionally versatile magnetic materials in use in high technologies. In this study, synthesis, characterization and assessment of potential for use in water remediation of two different types of nanostructured ferrites were performed. Barium hexaferrite (BaFe 12 O 19 , BHF) and strontium hexaferrite (SrFe 12 O 19 , SHF) nanoparticle preparation using a flash-combustion method was successful. The prepared samples were thoroughly characterized for their microstructure, morphology, elemental composition, functional groups, surface charge density and magnetic, dielectric and optical properties. The hexagonal phase was detected as the primary one in X-ray diffraction patterns, while vibrational spectrophotometry analyses demonstrated the presence of an M-type hexagonal structure. Temperature-dependent ferromagnetic behavior of the nanoparticles was indicated from the χ-T curves, with a slightly higher single transition temperature, T c , for BHF than for SFH: 675 °C vs. 650 °C. Despite having nanocrystalline structures, both BHF and SHF were identified as hard magnetic materials, with saturation magnetizations of 56.7 and 54.3 emu/g, respectively, and anisotropy fields greater than 9 kOe. Finally, batch adsorption studies were used to remove Pb(II) ions from aqueous solutions at various pHs and contact times using the as-prepared materials as fresh sorbents. The highest adsorption capacity was achieved at pH 7 and after 60 min of the contact time, equivalent to 84% and 80% for BHF and SHF, respectively. Extrinsic microstructural factors, such as particle morphology, surface area and porosity, proved to be more important for promoting the sequestration of Pb(II) than the intrinsic, crystallographic factors. Consequently, BHF performed better as an adsorbent than SHF under all of the tested conditions. The investigated nanostructured hexaferrites also demonstrated an exceptional recycling capacity. Graphical Abstract

In the present investigation, the distribution of iron ions at octahedral and tetrahedral sites in BaFe 12 O 19 prepared by employing four different synthesis techniques, namely, solid-state reaction, oxalate precursor route, sol–gel and wet chemical methods, have been examined using Mossbauer studies and compared with magnetization data. It was observed that the iron ions distribute in different preferential order at various sites for hexaferrites prepared using different synthesis methods, which is confirmed by Mossbauer spectroscopy. Prepared samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and Field emission scanning electron microscopy. Rietveld refinement of all samples revealed an M-type hexagonal structure confirming P63/mmc space group along with a minor peak belonging to the α-Fe 2 O 3 phase, except for the sample synthesized by sol–gel route. A uniform spherical shape with a small grain size was observed in sol–gel prepared samples and the Williamson–Hall method was adopted to estimate the average crystallite size, which varies between 72 and 129 nm. The room temperature magnetization studies reveal that the sample synthesized via sol–gel route shows high coercivity and saturation magnetization values due to their smaller grain sizes. Mossbauer spectra of all BaFe 12 O 19 samples were fitted with five sexets assigned to the hexagonal crystal structure of 4f 2 , 4f 1 , 2a, 12k and 2b sites, where the variation in their relative areas confirms the redistribution of iron ions at these sites. Graphical abstract

The microwave properties of epoxy composites filled with 30 wt.% of BaFe12–xGaxO19 (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.% BaFe12–xGaxO19/epoxy composites compared with binary 1% CNT/epoxy and 30 wt.% BaFe12–xGaxO19/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 Ga3+ concentration in the BaFe12–xGaxO19 filler and amplitude–frequency characteristics of the natural ferromagnetic resonance (NFMR) in 1 wt.%CNT/30 wt.% BaFe12–xGaxO19/epoxy composites was determined. Higher values of the resonance frequency fres (51.8–52.4 GHz) and weaker dependence of fres on the Ga3+ concentration were observed compared with pressed polycrystalline BaFe12–xGaxO19 (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.% BaFe12–xGaxO19/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.% BaFe12–xGaxO19/epoxy composite, and it slightly increased for the aligned 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composite.

The development of hexaferrite nanoparticles is scrutinized as potential sorbents for the removal of chromium (Cr) ions from aqueous chromium-containing solutions in a batch adsorption experiment. The transition metal Co doped BaFe 12 O 19 hexaferrite compounds (BHF) have been synthesized successfully via citrate auto combustion technique. The structure, surface morphology and magnetic properties of the samples were studied. X-ray diffraction pattern ratifies the existence of hexagonal phase as a main phase for the prepared samples. The average crystallite sizes are found in the range of 47–49 nm. The high-resolution transmission electron microscopy (HRTEM), as well as the Fourier, transform infrared spectrophotometry results confirm an M-type hexagonal structure existing. The χ-T indicates the temperature-dependent ferromagnetic behavior of BHF nanoparticles. The derivative shows a single transition temperature Tc at 698 °C, and 710 °C for BHF and BCHF respectively. The prepared samples are utilized as an adsorbent for the removal of Cr (VI) from the aqueous solution. The maximum adsorption capacity (qm) of Cr (VI) on the nano hexaferrite is higher than that of various other adsorbents testified in the literature. The pseudo-second-order kinetic model gives a better fit to the experimental data.

Here, we examine the efficacy of Al-doped Y-type hexaferrite-reinforced polyaniline composites as cutting-edge materials for optimizing electromagnetic shielding. “Ba 2 Co 2 Al 0.3 Fe 11.7 O 22 ” aluminium (Al) doped Y-type hexaferrite was synthesized via a low-cost sol–gel auto-combustion route and sintered at 1000 °C. A facile chemical method was utilized to prepare conducting polyaniline (PANI). Then, three composites with various compositions were synthesized via an in situ polymerization process, which was represented as FP-1 (95% Y-ferrite + 5% PANI), FP-2 (90% Y-ferrite + 10% PANI), and FP-3 (85% Y-ferrite + 15% PANI). X-ray diffraction (XRD) affirmed the formation of mono-phase hexagonal structured Y-type barium hexaferrite with higher degree crystallinity, and the measured approximated crystallite size of Y-ferrite/PANI nano-composites ranging from 53.59 to 30.62 nm. It was noted that with the inclusion of PANI, the lattice constant “c” first enhances and then diminishes, and an enhancement in the unit cell volume, porosity, dislocation density, and micro-strain. The investigation of Raman spectra affirmed the development of pure Y-ferrite and Y-ferrite/PANI nanocomposites. The pure Y-ferrite compound divulged sharp and intense peaks. However, the intensity of these vibration peaks diminished as the PANI content increased. Morphological analysis (FESEM) of Y-type hexagonal ferrite exhibited the development of coral-like grains with hexagonal forms, suitable for microwave absorption applications. The DC electrical resistivity at ambient temperature was measured as 2.67 × 10 9 Ω-cm for the Y-hexaferrite, and the resistivity of Y-ferrite/PANI nanocomposites reduced as PANI content heightened owing to the higher electrical conductivity of PANI as compared to the ferrites. The dielectric features of all the as-synthesized samples obeyed the Maxwell–Wagner model. Dielectric parameters, including dielectric constant/coefficient ( ε ′ ), dielectric loss ( ε ′ ′ ), tangent loss (Tanδ), and AC electrical conductivity ( σ ac ), depicted a positive correlation or direct proportionality with PANI content. Y-ferrite/PANI nano-composites exhibit versatile functionalities, which are promising for applications including energy storage, electronics, magnetic sensors, data storage, and electromagnetic shielding of microwaves.