Investigation of structural,magnetic and dielectric properties of SrM/PEEK: A potential microwave absorber

The current study aims to investigate the effect of Polyether Ether Ketone (PEEK) on the structural, magnetic, and microwave properties of substituted M-type SrFe_11.5Co_0.5O₁₂ (SrM) hexaferrite. Nanocomposites based on SrM/PEEK in ratios 4:0, 3:1, 2:2, and 0:4 were prepared by employing the micro-emulsion method. The composites were further characterized using XRD, SEM, FTIR, and VNA. XRD results exhibited a single-phase hexaferrite structure with an average crystallite size of 40 nm for pure SrM, which decreased due to increasing PEEK concentration. FESEM micrographs revealed the surface morphology and nature of the grains in the prepared nanocomposites. EDAX plots showed the presence of the constituent elements e.g., Fe, Sr, C, and O, at the respective standard energies. VSM results revealed the diamagnetic and ferromagnetic nature of PEEK and pure SrM/nanocomposite samples, respectively. FTIR spectra of SrM depicted the formation of hexaferrite due to the presence of Fe–O stretching peak at 525 cm^?1. Reflection loss was found to decrease due to increasing ferrite concentration in PEEK. This indicates that SrM/PEEK composites are potential microwave absorbers for microwave applications in the X band.     

Fast synthesis of SrFe12O19 hexaferrite in a single-mode microwave cavity

The M-type SrFe₁₂O₁₉ hexaferrite has been synthesized by a microwave solid state reaction process – a fast heating process – in a home-made 2.45 GHz single-mode microwave cavity. Starting from SrCO₃ and Fe₂O₃ mixtures (1:6 ratio), cold pressed samples have been heated up in the microwave electric field without needing any susceptor, demonstrating the good coupling of the precursors with this microwave mode in our experimental setup.After optimization of the experimental conditions, the properties of the obtained ceramics, including structure, microstructure and magnetic properties, are compared with those of ceramics synthesized by conventional solid state reaction. With that microwave process, it is found that SrFe₁₂O₁₉ ceramics prepared in less than 30 min exhibit magnetic properties similar to those of the same compound produced by a conventional process. This highlights the potentialities of the technique to synthesize hexaferrite ceramics.     

Enhanced microwave absorption features of Ba3Co2Fe24O41 hexaferrite by high lanthanium doping concentration

Controlling material structure and its electromagnetic properties, including complex permittivity and permeability, could enhance the microwave absorption performance of the material in terms of reflection loss and effective absorption bandwidth. In this study, La-substituted barium hexaferrite, Ba_3−xLa_xCo₂Fe₂₄O₄₁ (x = 0, 0.1, 0.3, and 0.5) compounds were successfully prepared using the solid-state reaction method, and their corresponding microstructures, static magnetic properties, and electromagnetic features in 2–18 GHz were investigated. The doping of La content increased saturation magnetization, coercivity, and remnant magnetization. The Ba_2.7La_0.3Co₂Fe₂₄O₄₁ epoxied sample with 3.5 mm thickness possessed an excellent microwave absorption of −47.3 dB at 3.52 GHz, and its corresponding effective absorption bandwidths were 3.75 GHz (2.25–6 GHz) and 0.57 GHz (17.43–18 GHz). It is shown that doping with various La concentrations on Ba₃Co₂Fe₂₄O₄₁ can be used as an effective technique to tune the performance of microwave absorbers based on barium hexaferrite.     

Enhancement in magnetic permeability of Ni-Co-Zn ferrites using CuO doping for RF and microwave devices

Novel soft magnetic ferrite materials will play a crucial role in next-generation trillion-dollar sensor technologies related to 5G communications and internet of things as these materials can achieve improved wireless power/signal transfer efficiency with high operation frequency. In this work, Ni_0.4Co_0.25Zn_0.35Fe₂O₄ ferrites with high permeability and low magnetic loss were prepared for RF and microwave device applications. Composition and microstructure control is crucial to obtain the desired magnetic and loss properties. CuO dopant (x = 0 wt% to 20 wt%) were employed during the synthesis of Ni_0.4Co_0.25Zn_0.35Fe₂O₄ ferrite specimens to modify the microstructures, thus improving the magnetic properties of the ferrites. High value of measured relative permeability (μ’ of 4-10) and relatively low magnetic loss tangent ( of 0.01-0.1) has been achieved at frequency range between 100 and 800 MHz. Addition of CuO, especially up to 3 wt%, can cause a significant increase in permeability. Real part of the permeability of 3.87 and 10.9 has been achieved for undoped and 3 wt% CuO doped specimens, while noticeable reduction in magnetic losses has been observed for the doped sample measured at 400 MHz. The resonance frequency of synthesized ferrites has also been shifted into GHz range, when higher concentration of CuO dopants (>5 wt%) were employed.     

Low-temperature sintering and high frequency properties of Cu-modified Co2Z hexaferrite

The low temperature sintering behaviors and high frequency properties of Cu-modified Co₂Z hexaferrites have been investigated. Normally, Cu-modified Co₂Z hexaferrite is difficult to be sintered at temperature lower than 1150 °C. By adding a small amount of sintering aid Bi₂O₃, Cu-modified Co₂Z ceramics with high density (more than 95% theoretical density) have been prepared successfully after sintering below 900 °C. The microstructures and properties are significantly influenced by the sintering temperature, the amount of Bi₂O₃ addition, as well as Cu content. The modified hexaferrite ceramics sintered at 900 °C, exhibited excellent high frequency properties, such as high initial permeability up to 6.6, high quality factor more than 30, high resistivity over 10⁹ Ω cm and good thermal stability. The experimental results show that these materials have a great potential as soft magnetic media for high frequency MLCIs applications.     

Microwave Sintering of Nanocrystalline Ni1−xZnxFe2O4 Ferrite Powder and Their Magnetic Properties

Nanocrystalline Ni_1?xZn_xFe₂O₄ (0 ≤ x ≤ 1.0) powder with grain size of 30 nm was prepared using the spraying‐coprecipitation method. The obtained nanocrystalline Ni_1?xZn_xFe₂O₄ powder was sintered using conventional and microwave sintering techniques. The results show that the microstructure and magnetic properties of the sintered samples are obviously improved by microwave sintering of nanocrystalline Ni_1?xZn_xFe₂O₄ ferrite powder. The initial permeability of Ni_1?xZn_xFe₂O₄ ferrite increases with the increase in zinc concentration, although its resonance frequencies shift from high frequency to low frequency. The maximum initial permeability for microwave‐sintered Ni_0.4Zn_0.6Fe₂O₄ ceramic obtained at the temperature of 1170°C for 30 min reaches up to 360.9, and its resonance frequency is ~10 MHz. It may be attributed to the nanocrystalline Ni_1?xZn_xFe₂O₄ raw powder as well as the microwave sintering process, which results in a synergistic effect on improvement of the microstructure and magnetic properties.     

Copper‐substituted spinel Zn‐Mg ferrite nanoparticles as potential heating agents for hyperthermia

Cu_xZn_0.5‐xMg_0.5Fe₂O₄ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) ferrite nanoparticles are synthesized via thermal treatment technique using polyvinyl alcohol (PVA) as a capping agent. The effect of Cu²⁺ ions substitution on the magnetic and structural properties of ZnMg ferrite nanoparticles is assessed. X‐ray diffraction (XRD) results prove the formation of spinel cubic ferrite with nanocrystalline structure. It is observed by increasing Cu²⁺ ions content in Cu²⁺‐substituted ZnMg ferrite samples, the lattice constant decreases. The field‐emission scanning electron microscopy (FESEM) micrographs indicate that all samples have sizes in nanometer scale with almost spherical morphology and ZnMg ferrite nanoparticles size is increased as the result of Cu²⁺ substitution. Magnetic data show that by increasing in Cu²⁺ content, the saturation magnetization (Ms) increases up to x = 0.3 and then declines with the addition of more Cu²⁺ ions in the samples. To assess the heat release of Cu²⁺‐substituted ZnMg ferrite nanoparticles, an alternating magnetic (AC) field is applied. The results show an upward trend for the samples in the temperature vs time chart, as a result of increasing in Ms of the samples. The Cu_0.3Zn_0.2Mg_0.5Fe₂O₄ sample exhibits a temperature increase up to 43°C during 510 seconds in the exposure of 125 Oe magnetic field intensity. The cell compatibility of the samples is investigated using osteoblast‐like cells (MG63). Results show that the substitution of Cu²⁺ significantly affects the cell compatibility of the ZnMg ferrite nanoparticles.     

Investigation of crystal structure,dielectric properties,impedance spectroscopy and magnetic properties of (1-x)BaTiO3 – (x)Ba0.9Ca0.1 Fe12O19 multiferroic composites

Composites having composition (1-x)BaTiO₃?(x)Ba_0.9Ca_0.1Fe₁₂O₁₉ (x = 0.10, 0.20, 0.30) were synthesized by conventional solid-state reaction technique. X-ray diffraction (XRD) was used to examine the phase formation. Rietveld refinement has been done using the FullProf suite which predicted the dual phase symmetry consisting hexagonal (P63/mmc) and tetragonal (P4mm) phases in the prepared composites. The dielectric properties of the obtained composites were investigated at different temperatures as a function of frequency in the range of 100 Hz to 7 MHz. The dielectric constant increases with an increase in Ca doped barium ferrite content. The composites showed usual dielectric dispersive behaviour with increasing frequency. The conduction mechanism and dielectric relaxation were examined by complex impedance spectroscopy (CIS). Nyquist plots of all composites showed two semicircles and their centers lied below the real axis. Magnetic characterization was performed by using a vibrating sample magnetometer (VSM) up to a field of 15 kOe at room temperature. The hysteresis loops reveal the ferromagnetic nature of the composites. The values of saturation magnetization, magnetic moment per formula unit, and corresponding coercivity increases with ferrite content and are maximum at x = 0.3. AC conductivity also increases with ferrite content. The variation of frequency exponent ‘n' of the power-law with temperature suggests that the overlapping large polaron tunneling (OLPT) model is appropriate to explain the mode of conduction in all samples.     

Dielectric and microwave absorption properties of TiAlCo ceramic fabricated by atmospheric plasma spraying

Composite TiAlCo powders (TiO₂, Co₃O₄ and Al₂O₃) were synthesized by spray–drying technology. The phase composition and morphology of synthesized powders were characterized by X-ray diffraction and scanning electron microscopy, respectively. Using above synthesized powders as starting materials, TiAlCo ceramic were successfully prepared by atmospheric plasma spraying (APS) with an internally fed powder torch. Electromagnetic parameters and microwave absorption properties of the prepared ceramic coatings were investigated in the frequency range from 8.2 to 12.4 GHz (X-band). It was found that both the real part and imaginary part of dielectric constant decreases with increasing Al₂O₃ content in the whole measured frequency region. Dielectric properties are closely related to the relaxation polarization and interfacial polarization and electric conductivity. Furthermore, by combination of the frequency selective surfaces (FSS) and prepared coatings, a double absorption band of the reflection loss spectra had been observed in X-band. The optimized reflection loss values exceeding −10 dB can be obtained in the frequency range of X-band when the coating thickness is only 1.8 mm, and the reflection loss is insensitive to incident angle from 0° to 45° for both transverse electromagnetic (TE) and transverse magnetic (TM) polarizations.     

Permeability spectra of planar M-type barium hexaferrites with high Snoek’s product by two-step sintering

High-frequency ferrite ceramics exhibiting high permeability and low magnetic loss have been recently attracting more and more attention owing to the rapid development of modern communication technologies. It is known that the magnetic performance of ferrites is strongly associated with the morphology of their polycrystalline structure. In this work, we focus on the control of grain growth and densification process for planar Co-Ti doped M-type barium hexaferrites, BaCo_xTi_xFe_12-xO₁₉, by one-step sintering (OSS) and two-step sintering (TSS) techniques. Experimental results indicate that a uniform and fine-grained microstructure is achieved by the TSS method. More importantly, the ferrites prepared by TSS demonstrate high permeability (µ' = 18-20), low magnetic loss (tan δ_m = 0.1-0.3), and high Snoek's product (>25 GHz) in the frequency range of 100-400 MHz. By fitting experimental data, we have determined that low magnetic loss is derived from the small damping coefficient of spin rotation in terms of Kittel's theory. Therefore, the TSS technique provides an effective and efficient approach to prepare planar BaM hexaferrite materials for ultra-high frequency (UHF) communication devices requiring low loss and high Snoek's product.     

Aqueous Solution Preparation,Structure, and Magnetic Properties of Nano-Granular ZnxFe3?xO4 Ferrite Films

This paper reports a simple and novel process for preparing nano-granular Zn_xFe_3−xO₄ ferrite films (0 ≤ x ≤ 0.99) on Ag-coated glass substrates in DMAB-Fe(NO₃)₃-Zn(NO₃)₂ solutions. The deposition process may be applied in preparing other cations-doped spinel ferrite films. The Zn content x in the Zn _x Fe_3−x O₄ films depends linearly on the Zn²⁺ ion concentration ranging from 0.0 to 1.0 mM in the aqueous solutions. With x increasing from 0 to 0.99, the lattice constant increases from 0.8399 to 0.8464 nm; and the microstructure of the films changes from the non-uniform nano-granules to the fine and uniform nano-granules of 50–60 nm in size. The saturation magnetization of the films first increases from 75 emu/g to the maximum 108 emu/g with x increasing from 0 to 0.33 and then decreases monotonously to 5 emu/g with x increasing from 0.33 to 0.99. Meanwhile, the coercive force decreases monotonously from 116 to 13 Oe.     

Substituted nickel ferrite coated MWCNT/PVDF based epoxy nanocomposite for microwave absorption

Metal-substituted spinel ferrite-based microwave absorbing materials (MAMs) are attracting significant attention due to their varied soft magnetic behaviour, and ease of synthesis. This work established the efficiency of Cd²⁺ substituted nickel ferrite coated MWCNT (with varied MWCNT loading) for X-band microwave absorption, in the presence of PVDF. The substituted ferrite was prepared with a facile solvothermal process. X-ray diffraction and vibrating sample magnetometer analysis confirmed the spinel structure of substituted ferrites and tuned magnetic behaviour of Cd²⁺ substituted ferrite structure, respectively. FESEM revealed a uniform coating of substituted ferrite on MWCNT and XPS confirmed Cd²⁺ substitution. Hybrid nanocomposites of ferrite coated MWCNT with PVDF, in the epoxy matrix, revealed superior microwave absorption for NiF-150_10 PV and CdNiF-150_10 PV with an absorber thickness of 3 mm in the X band. The absorption bandwidth with the RL below ?10 dB reached 3.9 GHz and 3.6 GHz for NiF-150_10 PV and CdNiF-150_10 PV, respectively. The microwave absorption mechanism was discussed in detail. The developed NiF-150_10 PV and CdNiF-150_10 PV composites can be used as lightweight, low thickness microwave absorbers in the defense and telecommunication industries.     

High-temperature dielectric properties and microwave absorption abilities of Bi1−xMgxFeO3 nanoparticles

BiFeO₃ (BFO) multiferroic nanoparticles have attracted increasing attention owing to the coexistence of ferroelectric and ferromagnetic properties. In this work, Bi_1−xMg_xFeO₃ (x = 0.05, 0.1, 0.15) multiferroic nanoparticles were synthesized by the sol-gel method. The electromagnetic properties and microwave absorption performance in the temperature range of 323–723 K at X-band were investigated. The qualified bandwidth (absorption intensity < −10 dB) of the Mg-doped BFO materials covers the whole X-band at 673 K, suggesting promising candidates as high-temperature electromagnetic absorbers.     

Fabrication and properties of high performance PEEK/Si3N4 nanocomposites

The crystallization, morphology, microhardness, scratch hardness, dynamic modulus, and wear behavior of high performance poly(ether‐ether‐ketone) (PEEK) matrix nanocomposites reinforced with 0 to 30 wt % silicon nitride (Si₃N₄) nanoparticles were reported. The crystallinity of PEEK nanocomposites increases at 2.5 wt % Si₃N₄ but, thereafter it decreases with increasing Si₃N₄ content due to the hindrance to the ordering of PEEK chains. The crystallization peak temperature and crystallization onset temperature increases by 14°C for 10 wt % nanocomposite. The melting temperature does not vary significantly with Si₃N₄ content. SEM shows almost uniform distribution of Si₃N₄ in the PEEK matrix. The Vickers microhardness and scratch hardness increases significantly up to 10 wt % Si₃N₄ content.The dynamic modulus of nanocomposites increases below and above T_g of PEEK. The specific wear rate of nanocomposites with 2.5 wt % Si₃N₄ is reduced significantly and it is lowest at 10 wt % Si₃N₄. However, the coefficient of friction of nanocomposites is more than that of pure PEEK. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Formation of BaFe12−xNbxO19 and its high electromagnetic wave absorption properties in millimeter wave frequency range

BaFe_12?xNb_xO₁₉ (BFNO, x=0‐0.6) powders with Nb⁵⁺ substituting for Fe³⁺ were prepared by sol‐gel method. The formation process and electromagnetic (EM) wave absorption properties of the BFNO are investigated in detail. With Nb⁵⁺ content increasing from x=0 to x=0.6, the formation temperature of barium ferrite phase without heat time increases from ~700°C to ~900°C, while the appearance temperature of typical plate grains decreases from ~1300°C to ~1100°C, and the crystallization ability decreases at 600°C‐900°C, while the grain size increases gradually at 1100°C‐1300°C. Increasing sintering temperature and time promote the formation of barium ferrite phase and grain growth in all the samples. The ε′ and ε″ of the sample with x=0.6 sintered at 1300°C for 3 hours reach highest of ~7.9 and ~0.95 over 26.5‐40 GHz. Multiresonance peaks in permeability decrease from 40+ GHz to ~30 GHz with x rising from 0 to 0.6. Ultimately, small RL_min of ~?42 dB, thin d_m of ~0.76 mm, and broad bandwidth of >12 GHz can be exhibited simultaneously around millimeter wave atmospheric window of 35 GHz.     

Sr(Ga0.5Nb0.5)1−xTixO3 Low‐Loss Microwave Dielectric Ceramics with Medium Dielectric Constant

The microwave dielectric properties of Sr(Ga_0.5Nb_0.5)_1?xTi_xO₃ (x = 0, 0.1, 0.2 and 0.3) ceramics have been investigated together with their microstructures. Single‐phase solid solutions are achieved in this series of ceramics. The ordering features are comprehensively analyzed by transmission electron microscopy and Raman spectroscopy. Local 1:1 ordering in B‐site leads to a double‐cubic structure with space group , while Ti substitution disrupts this 1:1 ordering between Ga and Nb, and the metastable ordering between Ti and (Ga + Nb) is speculated to form due to their large size difference. The dielectric constant and temperature coefficient of resonant frequency increase nonlinearly as x increases, while the Qf value decreases gradually. The variation trend of Qf value is mainly attributed to the intrinsic loss because of the increasing vibrational anharmonicity by Ti substitution. The ordering transition from short coherence, long‐range ordering to short‐range ordering with increasing Ti content has an agreeable and weak effect on the Qf value. The best combination of microwave dielectric properties is achieved for the composition of x = 0.3: ε_r = 46.6, Qf = 42 200 GHz and τ_f = 5.0 ppm/°C.     

Targeted design of polyaniline-graphene oxide,barium-strontium titanate,hard-soft ferrite,and polyester multi-phase nanocomposite for highly efficient microwave absorption

The current paper focuses on synthesizing a high-efficiency microwave absorber via incorporating the nanofillers of graphene oxide-polyaniline (GO-PANI), barium-strontium titanate (BST), and soft-hard ferrite within the polyester matrix. The nanocomposite magnets of (Ba_0.5Sr_0.5Fe₁₂O₁₉)_1-x hard/(CoFe₂O₄)_x soft (x = 0.2, 0.5, and 0.8) were prepared using sol-gel auto-combustion method. The GO-PANI and BST were successfully synthesized by in situ polymerization and improved polymerization, respectively. The phase structure, chemical structure, morphology, and microwave absorption properties of the synthesized nanocomposites were characterized by X-ray diffractometer (XRD), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM), vector network analyzer (VNA) techniques, respectively. The results showed that the synergistic effects of the combination of dielectric (BST), conductive (GO-PANI), and magnetic materials (hard-soft ferrites) provided the reflection loss values of less than ?20 dB (>99% absorption) in the X-band region. The minimum reflection loss of ?35 dB (>99.99% absorption) was obtained by the optimal formulation including (Ba_0.5Sr_0.5Fe₁₂O₁₉)_0.2 (CoFe₂O₄)_0.8, and the weight ratio of 1: 2 for both BST/soft-hard ferrite and hard-soft ferrite + BST/GO-PANI with the thickness of 1 mm. According to the results, the thickness factor plays a key role in improving the impedance matching. Consequently, the proposed nanocomposite can be employed as a novel kind of microwave absorbers with good impendence matching and high absorption.     

Development of novel magnetic-dielectric ceramics for enhancement of reflection loss in X band

The purpose of this research was to develop BaFe_9.5Al_1.5CrO₁₉-xCaCu₃Ti₄O₁₂ nanocomposites (x=10%, 20%, 30%, 40%, 50%) and investigate their structural and magnetic features. The substituted barium hexaferrite (BaFe_9.5Al_1.5CrO₁₉) nanoparticles and calcium copper titanate (CaCu₃Ti₄O₁₂) particles were synthesized by the auto-combustion sol-gel method. The structural, chemical composition and morphology of CaCu₃Ti₄O₁₂ (CCTO) and the nanocomposites were investigated by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The magnetic and microwave properties of nanocomposites were also investigated by vibrating sample magnetometer and vector network analyzer, respectively. The results confirmed that 1100 °C is the optimum synthesis temperature for CCTO, the mean particles size of the CCTO particles changing from 220 nm (at 850 °C) to 2.18 µm (1250 °C). The SEM micrograph revealed that in all of the BaM-xCCTO nanocomposites (x=10%, 20%, 30%, 40%, 50%), the CCTO dielectric particles were attached to the substituted barium hexaferrite nanoparticles, indicating the effectiveness of the adopted synthesis method. Due to the presence of a dielectric phase in the nanocomposites the saturation magnetization decreases from 22 emu/g to 12 emu/g. The coercive field was a slightly larger than substituted barium hexaferrite and increased from 5.558 kOe for substituted barium hexaferrite to 5.813 kOe for BaM-50CCTO due to hindered motion of the domain walls by the dielectric phase and also to the collective behavior of agglomerated barium ferrite nanoparticles. The BaM-30CCTO nanocomposite shows the highest value of reflection loss compared to other nanocomposites. The reflection dip frequency of BaM-30CCTO nanocomposite was −48.85 dB at 10.93 GHz.     

Physico-chemical investigation on mixed alkali metal ferrites prepared by solution combustion method – A comparative study

Mixed alkali metal nanoferrites of the compositions M_0.5−X/2Zn_XMn_0.05Fe_2.45−X/2O₄ (M = Li, Na and K), where x varies from 0→0.5 in steps of 0.1, have been prepared by solution combustion method. Powder X-ray diffraction analysis for all the samples show the formation of single phase cubic spinel structure. The lattice parameter increases linearly with Zn content, which is attributed to ionic size differences of the cations involved. Both X-ray as well as experimental densities show upward trend with increasing ‘x’ due to increase in the molecular weight of the ferrite composition. Mössbauer spectra display the superimposition of paramagnetic doublet over ferrimagnetic sextet with increasing diamagnetic ‘Zn’ content. The key magnetic properties of the ferrite obtained, such as saturation magnetization and Curie temperature have also been studied. The combustion method used for the synthesis is a rapid approach for direct conversion of the stoichiometric reactant solutions into fine nanoparticles of ferrite product at a temperature (600 °C) much lower than that of the conventional ceramic method. Scanning electron micrographs confirm the formation of nanosized ferrites.     

Preparation and properties of BaTi1−xSnxO3 multilayered ceramics

BaTi_1−xSn_xO₃ (BTS) powders, with x ranging from 0 to 0.15, were synthesized by solid-state reaction technique. The powders were pressed and sintered at 1370 °C. Obtained BTS ceramics were investigated by X-ray diffraction and dielectric properties measurements. It is found that Curie temperature decreases while dielectric constant increases with increasing of tin content. A monolithic multilayered ceramics with up to five layers of BTS with different amounts of Sn were prepared. Their dielectric properties were examined. Relatively high dielectric constants in a wide temperature range were obtained. It is noticed that BTS mono- and multilayered ceramics have better dielectric properties if they are additionally treated in microwave oven for 10 min, after sintering at 1370 °C.