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Investigation of structural, hysteresis and electromagnetic parameters for microwave absorption application in doped Ba–Sr hexagonal ferrites at X-band
Abstract
M-type Ba0.5Sr0.5CoxLaxFe12-2xO19 hexagonal ferrite has been synthesized by the conventional ceramic method. X-ray diffraction analysis confirmed formation of M-type hexagonal structure while scanning electron microscopy analysis revealed a reduction in grain size with the doping of Co2+ and La3+ ions. The electromagnetic/microwave absorption has been measured from 8.2 GHz to 12.4 GHz in the microwave frequency regime and substantiated through hysteresis parameters, quarter wavelength, impedance matching, loss mechanisms. The hysteresis parameters, derived from hysteresis loops, infer soft ferrite nature of compositions. The doping of Co2+ and La3+ decreases coercivity to 17 Oe in composition x = 0.2 and increases saturation magnetization to 74.2 emu/g in composition x = 1.0. The doping improves impedance matching and increases microwave absorption as well as absorption bandwidth in the prepared compositions. The pronounced multi-peaks of absorption have been observed in composition x = 0.2 and 0.4 in the investigated frequency region. The depicted reflection loss dips are tunable through doping and thickness of the compositions. The reflection loss increases to −43.33 dB in composition x = 0.2 at 10.75 GHz and 1.9 mm thickness. The composition x = 0.2 also shows −10 dB and −20 dB narrow absorption bandwidth of 300 MHz and 320 MHz respectively.
... The ferrite substrate is composed based on solid state reaction (standard ceramic method) & sintered in microwave furnace at 11000 C temperatures. From the literature survey, it is being observed that microwave absorbing properties of composite ferrite material vary with doping concentration and found to be good absorber at low doping [28]. So, we can achieve bandwidth enhancement by varying this. ...
... Where μ= permeability of material, ε = permittivity of material, t= thickness of material. This equation suggests that with the variation of parameters of material, large bandwidth enhancement is possible and it is being validated in the research done by H. Kaur et.al [28]. She has synthesized a M-type Ba-Sr hexagonal ferrite with varying doping concentration Co 2+ & La 3+ ions. ...
... We have prepared the Ga doped Ba-Sr hexagonal ferrite using standard ceramic method [28][30]. In this method, firstly raw material is taken and converted into different compositions. ...
An experimental study of microstrip patch antenna designed and fabricated on FR4 epoxy substrate is presented. Further a performance comparison of designed antenna is made with proposed design using Gallium doped Ba-Sr hexagonal ferrite substrate. Microstrip feed line is used for inputting the signal to antenna. The whole simulation is done on HFSS simulator (version 13.0).The center frequency for proposed antenna is 10GHz and is optimized for significant performance parameters viz return loss, bandwidth, VSWR and gain. It was observed that the designed antenna provides better results with ferrite substrate as compared to FR4 epoxy substrate showing -10db broad bandwidth of 4.2GHz in the frequency region 8.2GHz to 12.4GHz. Although, the results of other parameters like return loss, VSWR and gain are found to be optimum with FR4 substrate as compared to mentioned ferrite substrate. The prototype of proposed antenna with FR4 epoxy substrate is fabricated and tested to attain the experimental results. The measured results are found to be better than simulated results. Thus the proposed antenna structure can be considered suitable for microwave communication application in X-band.
... In addition, hexaferrite magnets are preferred in many applications due to their high chemical stability, electrical resistance, and improvable magnetic properties. Hexaferrite magnets are widely used in electric motors, transformers, inductors, data storage devices, electromagnetic wave absorbers, and microwave device that do not require very high-energy product magnets [16][17][18]. In addition, hexaferrite has been used in applications such as medical [19], magnetic separation [20], ferrofluids [21], and magnetic seals [22] thanks to their nano-size-based production in recent years. ...
... The cation substitution is an effective method to improve the magnetic properties of SrM and is one of the most researched subjects in the literature [34][35][36][37][38][39]. The addition of cation element has different effects on magnetic and other properties such as Mn, Co, Cr, Zn, Ti, Nd, Sm, La, In etc. [17,18,[40][41][42][43]. These effects vary according to the cation ionic radius and lattice position (Wyckoff positions of atoms) and the interaction between other cations and anions. ...
... Ferrite composites are the ones made from the combination of ferrites with 63 carbon, 75-81 metals, 77,78,81,82 rare earth metals, [82][83][84][85][86][87][88][89][90] and polymers, 91,92 etc. depending upon the respective outstanding characteristic. Ferrites possess good dielectric and magnetic properties which is the basic requirement of a MAM. ...
... 63 Similarly, carbon and its subfamilies are preferred due to good dielectric properties, 76-81 while metals and rare earth metals help in improving the permeability as well as permittivity of the composites. 77,78,[82][83][84][85][86][87][88][89][90][91][92] A. Why are ferrites doped with carbon? ...
With the advancement and up-gradation of wireless technology, people worldwide are surrounded by microwaves, however, with the brighter side comes the darker side too. These microwave/electromagnetic wireless signals interfere with the environment/mankind and are referred to as electromagnetic interference (EMI)/electromagnetic or microwave pollution. Microwave/electromagnetic absorbers are used to mitigate this EMI or electromagnetic pollution. Researchers have been working on microwave absorbents of different kinds to save humans, their gadgets, electronically printed cards, etc. to create a healthy and radiation-free environment. Recently, there is an advancement in different forms of ferrite absorbers. This review presents a description of what are ferrite-based microwave absorbers, the preparation method of absorbers, the working principle, and detailed insights involving necessary models and mechanisms regarding microwave absorption. It also encapsulates the description of how the ferrite composition, morphology, doping, reflection loss peaks, and matrix account for optimizing the performance of the absorbers. The history, origin, and ancestral use of microwave absorbers are mentioned, and how technological needs lead to advancement in ferrite microwave absorbers has also been discussed. A picture is portrayed of what are microwaves, their potential hazards, and how these hazards should be taken care of with the help of ferrite microwave absorbers.
... Therefore, electromagnetic pollutants could affect the environment [2]. This requires researchers to characterise materials that can absorb and dissipate electromagnetic waves [3][4][5][6][7][8][9][10]. In addition, the design of microwave absorbing devices is required in order to reduce or eliminate this problem [11]. ...
... Recently, ceramic composites based on alumina have attracted the attention of researchers, due to their excellent microwave absorption property and high dielectric property [1][2][3][4][5][6][7][8][9][10][11][12][13]. These properties are important in several fields, notably in telecommunications [14], stealth technology from airplanes, Interferences in television images of high-rise buildings [15], the design of microwave circuits and radar-absorbing materials (RAM) [13][14][15][16]. ...
Electromagnetic pollution has become a major problem affecting human health, which requires the scientific community to characterise materials that can solve this problem. In the present work, we studied the microwave absorption properties and complex permittivity of ZrB2/Al2O3 ceramic composites in the X-band by simulation. The composites studied are based on alumina and reinforced with ZrB2 particles. The concentration of ZrB2 particles by volume in these composites are 0%, 5%, 10% and 15%. The results obtained show, on the one hand, that the complex permittivity depends on the frequency, and on the other hand, the high content of ZrB2 remarkably increases the complex permittivity and improves the microwave absorption properties. The ZrB2/Al2O3 composite with 5% by volume of ZrB2 particles has better microwave absorption property than others. In this case, the minimum reflection loss is −26.36 dB at 11.5 GHz. For this composite, the RL bandwidth of less than −10 dB is 1.72 GHz, and it is obtained in the frequency range from 9.4 GHz to 10.5 GHz. The simulation results are in good agreement with the published experimental results. In addition, they indicate that the composites studied are favourable for microwave absorption applications in the X band.
... The six main categories of hexaferrite are M-type (AFe 12 [1]. Among different hexaferrites, M-type ferrites were extensively researched for high frequency applications [2][3][4]. In recent times, researchers have directed their attention towards W-type hexagonal ferrite for microwave antenna application due to its reasonable permeability, low electrical conductivity and ferromagnetic resonance in GHz range [5]. ...
Due to their highly malleable electromagnetic characteristics, W-type hexaferrite BaZn2Fe16O27 (Zn2W) shows significant promise as an emerging magnetic material for high-frequency applications. In this study, Mg²⁺ substituted Zn2W type hexaferrite; BaZn2−xMgxFe16O27 (x = 0.0, 0.5, 1.0, 1.5, 2.0) was synthesized via the co-precipitation route. The X-ray diffraction (XRD) analysis showed the formation of pure W-type phase at 1300 °C/4 h sintering. The bulk densities of compositions were between 4.4 and 4.8 g cc⁻¹. FESEM microstructure showed a dense morphology for all the composition except x = 0.5. The highest saturation magnetization (Ms = 70.5 emu g⁻¹) was observed for x = 1.0 composition. The permittivity (ε), permeability (µ), miniaturization factor (n) and characteristic impedance (Zi) values at 500 MHz were in the range 19.08–50.16, 9.59–11.93, 13.79–23.45 and 0.47–0.74 respectively. Ansys HFSS simulation results showed good antenna characteristics for x = 1.5 composition. Hence, it may be concluded that Mg²⁺ substituted Zn2W can be useful for ultra-high frequency antenna substrate applications.
... Extensive research has been carried out on SrFe 12 O 19 hexaferrite to optimize its structural and magnetic properties for its use in microwave devices, recording media, multiferroic, magnetic photocatalysts and hard magnetic ceramic applications [1][2][3][4][5][6][7]. Microstructural engineering to generate application requires the understanding of relationship between magnetic properties and the ions distribution. ...
SrFe12–2xNixZrxO19 (x = 0–0.9) ferrites were successfully synthesized through hydrothermal method using metal chloride as start materials. It exhibits very good hexagonal crystals with doping content x < 0.3, but deviate from hexagonal flakes with increasing doping, accompanied by some debris. XRD confirm that the impurity phase decrease with the increase of doping amount even though the sample annealed at 950 °C. After annealing at 1150 °C, It exhibits the absence of secondary phases of SrCO3. It was found the obvious preferred orientation and becomes more significant with the increase of doping amount. In addition, the deconvoluted XPS of Sr 3d and Zr 3d indicated the complexed coordination with high doping amount x > 0.5. Magnetic properties further validated the ions migration and multielectron transitions. The highest saturation magnetization value observed is 55.66 emu/g for the x = 0.3 sample. With dopant increasing, the coercivity decreases steadily from 840 to 190 Oe. Thus, the materials with high Ms and low Hc values could be suitable used in longitudinal magnetic recording media.
... The microstructure and various properties of the material are not only influenced by the synthesis method and processing conditions, but the substitution and co-substitution of metal cations (such as Al, In, Zn, Ti, Ga, La, Sc, Nd, Ni, Ce, Cu, Co) in place of Ba 2+ or Fe 3+ in BaFe 12 O 19 have also been observed to significantly impact the magnetic, electrical, and microwave properties of hexaferrite [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. The temperature of the ferrimagnetic-paramagnetic phase transition is observed to decrease almost linearly with the substitution of Al 3+ for Fe 3+ in BaFe 12 O 19 . ...
... In general, there can be resonances due to magnetic domains which can cause a non-monotonic frequency dependence of the permeability. Such domain wall resonance occurs at 1 GHz [67,73,74], however our examined frequency range (12)(13)(14)(15)(16)(17)(18) is much larger than this frequency. So, domain wall resonance is absent in the prepared composites. ...
Yttrium iron garnet ferrite (YIG), with good magnetic and dielectric properties, was mixed with doped
magnesium spinel ferrite (Y3Fe5O12(x)/Mg0.4Cd0.4Co0.2Fe2O4(1-x) (x = 0.3, 0.6, 0.9)) to attain high
permittivity and permeability with low magneto-dielectric losses. We have reported the synthesis
and enhanced structural, magnetic and magnetodielectric properties of composites for miniaturized
antenna applications. The X-ray diffraction (XRD) patterns of all the composites were analysed using
the Rietveld method, which confirmed that they exhibited a crystalline structure with a cubic spinel
and cubic garnet phase. XRD spectra confirm that the spinel ferrite phase dominates over the garnet
ferrite phase in the x = 0.3 composite, whereas it is the opposite for the other composites. In contrast
to the parent ferrites, it has been observed that the composites (x = 0.3, 0.6, 0.9) exhibit a higher
value of the crystallite size ‘D’ and a lower value of the lattice constant ‘a’. The composite with the
x = 0.3 composition has the least porosity and a high relative density. From field emission scanning
electron microscopy (FESEM), it has been ascertained that the materials possess a grain size ranging
from 0.57 to 0.8 µm, with a larger grain size for the x = 0.9 composite, while the x = 0.3 composite
has the smallest grain size. Transmission electron microscopy (TEM) scans have corroborated the
FESEM micrographs’ findings, indicating that the grains within the composites’ structure exhibit
agglomeration. The calculated values of inter-planar spacing of the samples using high-resolution TEM
(HR-TEM) matches well with the XRD results. A magnetic study reveals that the composite with x =
0.3 has a good exchange-coupling, the highest coercivity value of 99.2 Oe and a magnetization value of
41 emu/g. The composite with x = 0.3 also has the highest permittivity value of ∼19.5, a permeability
value of ∼2.8, but low dielectric and magnetic losses of ∼0.009 and ∼0.002, respectively. These low
losses and a high miniaturization factor of ∼7.2 at high frequency (14 GHz) make it a potential
candidate for high-speed satellite antenna applications.
... Doping of metal ferrite nanoparticles (NPs) exhibit several physicochemical features that are significantly different from bulk materials because of their existence in an extremely smaller size range domain and having a higher surface area. Ferrite materials have different kinds such as hexagonal, garnet, and spinel structure basically depending on the crystal lattice [25][26][27]. Spinel ferrites MFe 2 O 4 (M: Fe, Co, Ni), which come in inverse and normal forms, are the most intriguing of the various formations [28]. Among all the spinel ferrites, CoFe 2 O 4 (CFO) is an inverse spinel structure of AB 2 O 4 type where the 'A'site identifies a divalent metal ion and the 'B' site identify a trivalent metal ion. ...
Hexa-spinel ferrite nanoparticles of Cobalt Lead Ferrite (CPFO)were prepared by a flash auto combustion method, while xCPFO/PS (x = 0, 2.5, 5, and 7.5 wt.%) nanocomposite films were synthesized by casting method. The diffraction pattern Rietweld refinement of CPFO nanoparticles confirmed the formation of two phases; face-centered cubic spinel and hexagonal structure. HRTEM micrographs of Cobalt Lead Ferrite (CPFO) nanoparticles shows average particle size around 30 nm. FESEM cross-section images of CPFO/PS nanocomposite films showed CPFO nanoparticles dispersed in PS matrix. All optical characteristics of the synthesized nanocomposite films, including absorbance, transmittance, direct and indirect energy band gap, Urbach energy, excitation coefficient and refractive index were investigated using a UV-visible spectrophotometer examination. The direct optical energy band gap lowered from 4.533 eV to 4.368 eV and the indirect energy optical bandgap lowered from 4.337 eV to 4.146 eV while the Urbach energy raised from 0.103 eV to 0.209 eV with increasing the nanofillers from 0 to 7.5 wt.%. Broad-band dielectric spectroscopy was used through a wide frequency range (0.1Hz-1MHz). The dielectric real permittivity (ε′), the dissipation factor tan (δ) and the electric modulus (M′&M′′) measurements were studied. CPFO nanoparticles addition significantly enhanced the dielectric real permittivity (ε′), the dissipation factor tan (δ) and ac conductivity of all nanocomposites.
... Functional magnetic materials, and in particular complex magnetic oxides [1][2][3][4][5] and composites based on them [6,7], attract great attention nowadays. It concerns the correlation between their composition, structural parameters, and physical and chemical properties [8][9][10][11][12]. Complex magnetic oxides based on iron oxides (ferrites) are widely investigated and frequently used as perspective materials for permanent magnets [2], catalytic applications [10], high-frequency applications [12][13][14], and sensors based on the multiferroic effect [15,16]. ...
... Functional magnetic materials, and in particular complex magnetic oxides [1][2][3][4][5] and composites based on them [6,7], attract great attention nowadays. It concerns the correlation between their composition, structural parameters, and physical and chemical properties [8][9][10][11][12]. Complex magnetic oxides based on iron oxides (ferrites) are widely investigated and frequently used as perspective materials for permanent magnets [2], catalytic applications [10], high-frequency applications [12][13][14], and sensors based on the multiferroic effect [15,16]. ...
... If the frequency is kept low, the electrons get assembled at the dielectric constant stretches to the peak worth; similarly, if the polarization is decreased, higher frequencies are required. Because the desired frequency does not match the relevant given frequency, there is a dielectric loss as a result [1,38] reported similar findings [39]. ...
Praseodymium (III)-doped M-type SrPrxFe12-xO19 (x = 0.00, 0.25, 0.50, 0.75, 1.00) hexa-ferrites were synthesized via micro-emulsion process followed by annealing of samples at 800 °C for 4 h. The effects of praseodymium particles on properties such as electrical, magnetic, and dielectric were studied. Via TGA the phase formation was observed to be started at 900 °C, and weight reduced to 5.27% at 1010 °C. Through X-ray diffraction (XRD), hexagonal structure was confirmed and structural properties were studied: the crystalline size, lattice constant, bulk and X-rays densities, i.e., 4.446 nm, 5.90 Å, 4.167 g·cm−3 and 6.46 g·cm−3, respectively. The cation dispersion and shifting of frequencies were observed by FTIR at frequencies 430–590 cm−1 because of dopant of higher radii. Surface morphology, grain structure, and porosity were studied by scanning electron microscopy (SEM). Electrical properties were determined by impedance spectroscopy. The impact of Pr3+ doping on distinct metrics, i.e. dielectric constants, dielectric loss, tan loss, A.C conductivity, was studied: 1.890, 0.023, 0.012, 0.001, respectively. The effects of Pr3+ doping on retentivity, coercivity, saturation magnetization, and anisotropy were investigated by the vibrating sample magnetometer (VSM). The increase in saturation and remanence is due to the increase of Pr3+ that retuned extra Fe3+ ions from the lattice plot. The prepared materials offer valuable potential for applications of high-density recording medium applications and high-frequency devices.
... Functional magnetic materials, and in particular complex magnetic oxides [1][2][3][4][5][6][7] and composites based on it [8,9], attract great attention nowadays. It concerns the correlation between their composition, structural parameters, and physical and chemical properties [10][11][12][13][14]. Complex magnetic oxides based on iron oxides (ferrites) are widely investigated and frequently used as perspective materials for permanent magnets [6], electrotechnical applications [15], high-frequency applications [16][17][18], and sensors based on the multiferroic effect [19,20]. Hexagonal ferrites have considerable importance due to their fascinating magnetic and dielectric properties. ...
Herein, using first-principles density functional theory (DFT) calculations, we have investigated the effects of Bi substitution on the structural, electronic, and magnetic properties of barium hexaferrite (BaFe12-xBixO19, x = 0; 0.5; 1.5 and 2). As a result of the calculation, it was determined that the most stable structure exists if the spin of the Fe atom on the 2a, 2b, and 12k positions of the barium hexaferrite compound is taken in the upward direction. The calculated lattice constant
and magnetic moment
of iron ions are in reasonable agreement with other experimental works. Moreover, the presence of bismuth reduces the electronic band gap. Energy gain and magnetic anisotropy energy calculations for FIM, FM, and NM states were performed for the most stable states. It has been established that the most stable structural state is characteristic of х = 0.5. It has been calculated that substitution by the large Bi3+ ion dramatically changed the electronic structure and sharply reduced the band gap. This paper is the first step towards establishing the nature of the distribution of ions in M-type hexaferrites under conditions of substitution by ions with a large ionic radius.
... Soft ferrite is widely used for many types of magnetic devices such as high frequency transformers, inductors, magnetic heads and microwave or high frequency absorber applications (Singh et al. 2016Kaur et al. 2019;Joshi et al. 2017;Nandotaria et al. 2018); because, they have higher electrical resistance compared to soft magnetic alloys. Various replacements have been taken into consideration in order to achieve the desirable electrical and magnetic properties. ...
Nickel-copper ferrite nanoparticles NixCu1-x Fe2O4 with values x = 0.3, 0.5,0.7 fabricated by combustion method. X-ray diffraction (XRD) analyzes confirmed the formation of the ferrite structure. The average size of crystals was estimated to range from 39 to 44 nm. The particle morphology was detected and interpreted by the FSEM scanning microscope and the porosity characteristic of the ferrite structure based on the combustion method was observed. The FTIR analysis was performed to investigate the bonds in which the tensile vibrational mode of the tetrahedral site in the range of the wavelength of 500–600 cm−1.The magnetic properties of nanoparticles were investigated using VSM analysis and the effect of increasing of copper ion on MS saturation magnetization and HC coercivity force was investigated. With respect to the saturation magnetization values for the synthesized samples, it was observed that by increasing the Cu content from x = .3 to x = .5 the saturation magnetization decreased and then increasing with increasing Cu content such that at x = .5, we had the lowest saturation magnetism. Reduction of saturation magnetization Copper ions occupy ferric ions in tetrahedral sites and iron ions are transferred to octahedral sites. The results of UV–Vis indicate to complete absorption in the samples. The linearity of the edge of the absorption spectrum relates to a direct energy band gap and the effect of increasing copper ions on ferrite conductivity was investigated.
... The enhancement of wireless technology in our daily life has arisen the problems related to the electromagnetic interference and EM pollution [1][2][3]. To overcome the issue, the researchers have made continued efforts to develop the material that absorbs electromagnetic radiation and avoid electromagnetic interference. ...
Microwave absorbing composites comprising of Zinc Ferrite and Activated Charcoal (AC) are synthesized by mechanical alloying method. The low-density zinc spinel ferrite is synthesized by auto combustion method. Activated charcoal is produced by using high energy planetary ball mill. The composites comprising of activated charcoal and zinc ferrite are developed by using ball milling method. The as-synthesized zinc ferrite is observed to have a saturation magnetization of 35.15 emu/g. The addition of AC in the ferrite matrix results in gradual decrease in the saturation magnetization. The influences of activated charcoal on the magnetic and dielectric properties of zinc ferrite are also explored for microwave absorption applications in X-band. The composite medium containing 25% zinc ferrite and 75% activated charcoal showed excellent microwave absorbing behavior in X-band. It achieves a minimum reflection loss of −14.46 dB at 9.27 GHz with effective coating thickness of 2.3 mm.
Graphical abstract
... The EMI induces spurious fields through the medium, for example electrical or electronic devices, it passes through causing the malfunctioning of devices. This has motivated researchers to explore materials in the form of microwave absorbers or radar absorbing materials (RAM), anti-electromagnetic interference coatings and electromagnetic interference (EMI) suppressors [14,15]. Ferrites are good electromagnetic interference (EMI) suppressors in comparison with dielectric counterparts due to their excellent dielectric and magnetic properties [16]. ...
Composites of yttrium barium orthoferrite (Y0.5Ba0.5FeO3) and nickel-substituted strontium hexaferrite (SrNi0.25Fe11.75O19) with an Equation (1 − x) YBF – (x) SNFO (YBF/SNFO) with x = 0, 0.2, 0.5, 0.8 and 1 have been investigated, and the conventional solid-state reaction (SSR) method was utilized for the synthesis process. The structural, morphological, optical and magnetic properties of the synthesized composites have been systematically investigated. The coexistence of YBF and SNFO phases and phase purity gets confirmed by X-ray diffraction (XRD) and field emission scanning electron microscopic (FESEM) analysis. The average particle size calculated by using image J software is in the 180–290 nm range. The characteristic peaks in the FTIR spectra shift toward higher wave number on increasing the SNFO phase in the composite. The optical energy band gap is in the range of 1.57–1.75 eV and increases with increasing the SNFO phase in the composite suggesting such materials as a candidate for optical applications. Magnetic properties of the composites revealed the increasing nature of saturation magnetization with increasing the value of SNFO content in the composite. The squareness ratio (Mr/Ms) value confirmed the multiple domain structure of x = 0 and 0.2 compositions and single magnetic domain structure of x = 0.8 and 1 compositions of the prepared samples.
... [61][62][63] According to the initial crystal lattice of ferrites, their structures are garnet, hexagonal, and spinel. [64][65][66] Among these structures, normal and inverse spinel ferrites are very attractive. Cobalt and iron oxides have higher magnetic properties compared to other ferrites. ...
Herein, a concise review of the latest developments in catalytic processes involving organic reactions is presented, focusing on magnetic catalytic systems (MCSs). In recent years, various micro- and nanoscale magnetic catalysts have been prepared through different methods based on optimized reaction conditions and utilized in complex organic synthesis or degradation reactions of pharmaceutical compounds. These biodegradable, biocompatible and eco-benign MCSs have achieved the principles of green chemistry, and thus their usage is highly advocated. In addition, MCSs can shorten the reaction time, effectively accelerate reactions, and significantly upgrade both pharmaceutical synthesis and degradation mechanisms by preventing unwanted side reactions. Moreover, the other significant benefits of MCSs include their convenient magnetic separation, high stability and reusability, inexpensive raw materials, facile preparation routes, and surface functionalization. In this review, our aim is to present at the recent improvements in the structure of versatile MCSs and their characteristics, i.e., magnetization, recyclability, structural stability, turnover number (TON), and turnover frequency (TOF). Concisely, different hybrid and multifunctional MCSs are discussed. Additionally, the applications of MCSs for the synthesis of different pharmaceutical ingredients and degradation of organic wastewater contaminants such as toxic dyes and drugs are demonstrated. This journal is
... Although the absorption of electromagnetic waves by this material is not the best, we can find that with the doping of Ti 4+ ions, the absorbing properties of M-type barium ferrite have changed significantly. This change is mainly due to the transition of trivalent Fe ions to divalent Fe ions, which affects the permeability of the material and the impedance matching, and broadens the absorbing effect at high frequencies [47][48][49]. Figure 7(a) shows the relationship between bandwidth and RL of BFTO-x samples, and the maximum RL and bandwidth are listed in Table 3. For x = 0.2, the greatest loss can be obtained at the thickness of 1.8 mm, and the bandwidth can reach to 5.28 GHz at 2 mm when RL is less than −10 dB, while the bandwidth of the other three components is about 3 GHz. ...
The barium ferrite BaTixFe12-xO19 (x = 0.2, 0.4, 0.6, 0.8) (BFTO-x) ceramics doped by Ti⁴⁺ were synthesized by a modified sol-gel method. The crystal structure and magnetic structure of the samples were determined by neutron diffraction, and confirm that the BFTO-x ceramics were high quality single phase with sheet microstructure. With x increasing from 0.2 to 0.8, the saturation magnetization (Ms) decreases gradually but the change trend of coercivity (Hc) is complex under the synergy of the changed grain size and the magnetic crystal anisotropy field. Relying on the high valence of Ti⁴⁺, double resonance peaks are obtained in the curves of the imaginary part of magnetic conductivity (μ′′) and the resonance peaks could move toward the low frequency with the increase of x, which facilitate the samples perform an excellent wideband modulation microwave absorption property. In the x = 0.2 sample, the maximum reflection loss (RL) can reach -44.9 dB at the thickness of only 1.8 mm, and the bandwidth could reach 5.28 GHz at 2 mm when RL is less than -10 dB. All the BFTO-x ceramics show excellent frequency modulation ability varying from 18 (x = 0.8) to 4 GHz (x = 0.4), which covers 81% of the investigated frequency in microwave absorption field. This work not only implements the tunable of electromagnetic parameters but also broadens the application of high-performance microwave absorption devices.
... Ferrites are very important magnetic materials, widely used in high frequency and microwave technology fields [1][2][3][4][5]. Spinel ferrites are important ferrite materials and used in many electronic components, such as transformers, inductors, converters and anti-electromagnetic interference filters [6][7][8]. ...
NixFe3−xO4 ferrites (x = 0.6, 0.7, 0.8, 0.9, 1.0) were prepared by solid-phase reaction method. Structure and morphology were characterized by X-ray diffractometer (XRD) and scanning electron microscope (SEM). Magnetic properties were measured with B-H analyzer and magnetic properties measurement system (MPMS). NixFe3−xO4 ferrites with high Ni²⁺ content (x = 0.7 ~ 1.0) present pure cubic spinel phase and dense microstructure. Their saturation magnetization (Ms) and initial permeability (μi) decrease with x increasing. Temperature coefficient (αμ) and specific temperature coefficient (β) were calculated based on the permeability from -60 °C to 100 °C. The results show both of αμ and β decrease with x decreasing, indicating that proper reduction of Ni²⁺ content and increasing Fe²⁺ content help to improve the temperature stability of NixFe3-xO4. This improvement in temperature stability is attributed to the influence of Fe²⁺ in the ferrites on the magnetocrystalline anisotropy.
The MgTiTa2O8 ceramics were synthesized in the molten salt KCl. We have conducted an examination of the phases, microstructure, and microwave dielectric characteristics of MgTiTa2O8 ceramics. This investigation involved the use of X-ray diffraction (XRD), Rietveld refinement, and scanning electron microscopy (SEM). The result demonstrated that MgTiTa2O8 ceramics exhibited crystallization into a tri-rutile structure with space group P42/mnm (136). With the increase of temperature, the relative density gradually increases, which benefit the dielectric constant and Q × f value. However, as the temperature continues to rise, there is a decrease in the εr and Q × f value, which can be ascribed to over-sintering of the sample and a resultant reduction in the uniformity of grain size. The correlation between oxygen octahedron distortion dielectric, bond strength, packing fraction, and properties of microwave is discussed. The Q × f value increases with the increase of atomic packing density. The value of τf decreases with the increase of bond energy and has no direct relation with the distortion of oxygen octahedron. The MgTiTa2O8 ceramics sintered at 1150 °C exhibited superior dielectric characteristics of εr = 35.1, Q × f = 32,200 GHz, τf = + 95.4 ppm/°C.
The main theme of this work is to synthesize and investigate different properties of Pr ³⁺ ‐Cu ²⁺ substituted X‐type hexaferrite Sr 2‐x Pr x Co 2 Fe 28‐y Cu y O 46 with concentration (x = 0, 0.02, 0.06, 0.1 and y = 0, 0.1, 0.3, 0.5) by adopting the sol–gel method. The XRD patterns show the single phase for all the samples. The Pr ³⁺ ‐Cu ²⁺ substitution in pure X‐type hexaferrites changes the structural parameters. The increment in dielectric properties with Pr ³⁺ ‐Cu ²⁺ substitution is observed and the patterns show anomalous dielectric behavior. The FTIR analysis also confirms the single phase for the prepared materials. The magnetic properties of the material are enhanced with additives. The difference in saturation magnetization, coercivity, and remanence is observed on the basis of allocated cations onto the different lattice sites. The linear increase in saturation magnetization, remanence, and coercivity make them useful as permanent magnets. The thermal analysis is carried out to know the sintering temperature at which the single X‐type phase can be attained. The material exhibits the minimum value of reflection loss (microwave absorption) at higher frequencies that make this material useful to act as microwave absorbing material (MAM) for super high frequency (SHF) devices.
With the advent of 5 G technologies, developing microwave-absorbing materials is an urgent need to address the issues caused by harmful electromagnetic pollution. For this purpose, a novel ferrite series with composition Zn0.25Co0.75(MnZr)xFe2–2xO4 (0.05 ≤ x ≤ 0.25, ∆x = 0.05) was successfully synthesized using the sol-gel citrate route. Also, the effects of the co-substitution of Mn and Zr on the structural, morphological, magnetic, electromagnetic, and microwave absorption characteristics of zinc-cobalt spinel ferrites were studied. The X-ray diffraction patterns indicated the formation of nanoparticles having a cubic spinel lattice structure. Coercivity was found to decrease whereas saturation magnetization increased with the increasing level of substitution from MZ 0.05 to MZ 0.25. In Ka-band, the experimental results showed that MZ 0.15 outperformed all the prepared compositions by exhibiting a minimum reflection loss of −27.99 dB and an efficient absorption bandwidth of 6.5 GHz at a narrow sample thickness of 2.2 mm. The simulation performed by varying the sample thickness revealed that the high values of gross loss tangent and excellent impedance matching lead the composition MZ 0.20 to achieve the optimum value of reflection loss of − 42.71 dB at a matching frequency of 29.20 GHz and a matching thickness of 1.1 mm. These findings suggested that the fabricated materials prove to be efficient absorbers in the 26.5–40 GHz frequency range.
The magneto-optical and dielectric behavior of M-type hexaferrites as permanent magnets in the THz band is essential for potential applications like microwave absorbers and antennas, while are rarely reported in recent years. In this work, single-phase SrFe12-xNbxO19 hexaferrite ceramics were prepared by the conventional solid-state sintering method. Temperature dependence of dielectric parameters was investigated here to determine the relationship between dielectric response and magnetic phase transition. The saturated magnetization increases by nearly 12%, while the coercive field decreases by 30% in the x = 0.03 composition compared to that of the x = 0.00 sample. Besides, the Nb substitution improves the magneto-optical behavior in the THz band by comparing the Faraday rotation parameter from 0.75 (x = 0.00) to 1.30 (x = 0.03). The changes in the magnetic properties are explained by a composition-driven increase of the net magnetic moment and enhanced ferromagnetic exchange coupling. The substitution of the donor dopant Nb on the Fe site is a feasible way to obtain multifunctional M-type hexaferrites as preferred candidates for permanent magnets, sensors, and other electronic devices.
CoNi alloys are well known as excellent magnetic microwave absorption materials, but their various structures greatly influence electromagnetic properties, especially chains versus particles. Hierarchical CoNi chains were prepared using the solvothermal method in conjunction with an external magnetic field, and hierarchical CoNi particles were obtained in the absence of the magnetic field. Changing the reaction time from 6 to 12 h can change the surface structures of hierarchical CoNi alloys, as seen in the SEM images. The lattice parameters of samples are determined by XRD results, which include crystalline structures, lattice constants, mean crystallite sizes, and internal strain. The investigation of magnetic properties indicates that CoNi chains possess a stronger saturation magnetization and higher coercivity than CoNi particles as a result of their higher aspect ratios and larger crystalline sizes. Furthermore, CoNi chains have a higher microwave absorption capacity than CoNi particles, with a minimum reflection loss value of –42.113 dB (16.5 GHz) and an effective absorption bandwidth of 3.5 GHz (13–16.5 GHz). Conductive loss, defect-induced polarization relaxation, eddy current effect, exchange resonance, Néel relaxations, multiple reflections, and scatterings all contribute to the excellent microwave absorption performance of the CoNi chains. This research establishes that a chain-like structure outperforms a particle-like structure for hierarchical CoNi alloys as microwave absorbers, and it will provide clear guidance for designing high-performance magnetic microwave absorption materials.
This research project was designed to understand the synergetic effect of trivalent ion Yb³⁺ and divalent ion Cu²⁺ co-substitution on different properties of X-type hexagonal nano ferrites.For this purpose, a series of Sr2-xNi2YbXFe28-YCuYO46 X-type hexagonal nano ferrites with concentration (x = 0, 0.02, 0.06, 0.1 & y = 0, 0.1, 0.2, 0.3) was synthesized by adopting the sol gel method. The XRD (X-ray diffraction) results of synthesized samples reveal the formation of single phase for all samples with space group P63/mmc. All the XRD peaks coincided with the reference card (ICDD # 01-073-2034). The theoretical fitting was performed by implementing the Rietveld refinement method to further check the single phase of the samples. The crystallite size and unit cell volume decrease with increasing Yb³⁺ and Cu²⁺ contents. The VSM results indicated the hard magnetic nature of all the synthesized materials and theoretically calculated particle size was varied in the range between 9.2-11.5 nm. The saturation (Ms) and remanence magnetization (Mr) decreased with the increase in Yb–Cu contents. The value of coercivity (Hc) was first increased and then decreased with the substitutions. Furthermore, the Law of approach to saturation (LAS) was employed to theoretically fit the hysteresis loops. The mixture of spherical and rod shape grains was observed in the SEM micrographs. By adopting the line intercept method, the calculated grain size was varied in the range from 0.691-1.33μm. FTIR spectrum exhibits no extra absorption band due to residual material which also confirms the formation of single hexagonal phase structure. The Thermo gravimetric (TGA) analysis divulged the weight losses due to removal of nitrate, vaporization of water molecules and removal of organic compounds at different temperatures. The reflection loss (RL) values have been enhanced with the substitution of Yb–Cu contents.
Neodymium-doped nickel spinel ferrite, NiNdxFe2−xO4 (x = 0.00, 0.02, 0.04, 0.06) nanoparticles are synthesized by adopting the sol gel method. The formation of pure phase nickel ferrite is confirmed through XRD analysis. Neodymium is doped to tune the structural, magnetic, and morphological properties of nickel spinel ferrite nanoparticles. The ‘as synthesized’ undoped nanoparticles show the spherical shaped morphology with an average particle size ranging from 145 to 150 nm. It has been observed that the average particle size decreases with increasing the doping concentration of neodymium in nickel spinel ferrite. The effect of substituting the Fe³⁺ ions with Nd³⁺ ions on the electromagnetic properties of the developed material are also investigated using vector network analyzer. The nickel spinel ferrite with the doping concentration of x = 0.06 shows the best impedance matching with free space having normalized impedance matching of 0.96. The maximum attenuation constant of 78.51 is observed for NiNdxFe2−xO4 (x = 0.06). The reflection loss is measured with in a frequency ranging from 8.2 to 12.4 GHz. The maximum reflection loss of − 13.76 dB at 9.28 GHz for NiNdxFe2−xO4 (x = 0.06) is observed for the pellet of thickness 2.9 mm. The present study reveals that the neodymium-doped nickel spinel ferrite is the budding aspirant for microwave absorption application in X-Band.
In this work, TiN-embedded in N-doped carbon nanofiber (TiN/NCNF) composites were synthesized by the electrospinning method and heat treatment process subsequently. The TiN/NCNF composites possess different TiN nanoparticles (TiNNPs) content, which can acquire by tuning the percentage of TiNNPs in the polyacrylonitrile precursor solutions. The study shows that TiN/NCNF composites hold more intense and tunable electromagnetic wave (EMW) absorption capabilities, as the embedded TiNNPs with more defects lead to enhanced electrical conductivity and cause room-temperature ferromagnetic. As a result, TiN/NCNF composites can achieve the well-matched impedance and contribute to significant electromagnetic wave attenuation capabilities due to their more interfacial polarization, defect dipole relaxation polarization, enhanced conductance loss, and magnetic loss caused by the defect, resulting in excellent microwave absorbing performance. When the mass fraction of the TiN/NCNF composites (S2 sample with nominal 3 wt% TiNNPs content) was only 30% in the absorbing coating, the optimal reflection loss (RL) value was achieved in -45.19 dB at 15.6 GHz with a thickness of 1.91 mm, corresponding efficient absorption bandwidth (RL≤−10 dB) of 4.93 GHz.
This work provides a novel method of realizing lightweight, wide-bandwidth, and efficient microwave absorbing characteristics of carbon fiber absorbents, using obtained particles from defect engineering strategies as loaded ones. As may be expected, the TiN/NCNF composites would have a significant potential application prospect as microwave absorbing materials.
M-type barium hexaferrite with composition BaCo0.2Ti0.2Fe11.6 O19 was synthesized by sol-gel method and nanocomposites of Reduce Graphene Oxide/BaCo0.2Ti0.2Fe11.6O19 were also synthesized by hydrothermal method. The electromagnetic (EM) characteristics were studied in the frequency range of 2-18 GHz. The x-ray diffraction analysis confirms the formation of required nanocomposites and Scanning Electron Microscopy (SEM) analysis depicts the spherical morphology of BaCo0.2Ti0.2Fe11.6O19 (BCTF) nanoparticles, which are embedded in Reduce Graphene Oxide (RGO) sheets. The Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy confirm the purity of required phases. The Raman Spectra shows that ID/IG ratio increases from 0.967 to 1.379 for RGO/BCTF nanocomposites and produce defects in the sample. The magnetic properties were measured by vibrating sample magnetometer (VSM) in the magnetic field ranged from ± 12000 Oe. The RGO/BCTF transforms in to soft ferrite by the doping of Co²⁺ and Ti⁴⁺ cation in M-type hexagonal ferrite. The complex permittivity and permeability were measured by vector network analyzer in the frequency range of 2-18 GHz. The minimum Reflections Loss (RL) reached -18.24 dB for RGO/BCTF at frequency of 6.8 GHz with a thickness of 2 mm and also broadens the effective absorption bandwidth from 3.77 to 4.5 GHz. The effect of coating thickness (1-2mm) transforms the absorption peaks towards higher frequency with decrease in matching thickness.
Recently, widespread microwave applications have generated plenty of unwanted electromagnetic radiation, which has become a global environmental pollution problem. Therefore, finding an efficient microwave absorbing material (MAM) is a trendy topic, and strontium hexaferrite (SrFe12O19, SrM) is a promising candidate. However, its high ferromagnetic resonance frequency (fFMR) prevents SrM from becoming an excellent MAM for wide-frequency range applications. Herein, as-prepared SrM samples with the morphologies of polygonal shape (Sr-P), rod (Sr-R), and porous ball-like (Sr-PH) were successfully prepared. Differences in morphology were effective to the static magnetic and optical properties. Furthermore, the fFMR of SrM was modified to the X-band frequency range. In particular, Sr-PH samples could reach reflection loss (RL) values of – 10 dB for 2.5 and 3 mm thicknesses. The microwave absorption of SrM as-prepared samples could be enhanced by making the tri-layer microwave absorbers from as-prepared samples. The simulated RL curves of the 2mm tri-layer-absorber with Sr-PH as the top layer, Sr-R as the middle layer, and Sr-P as the bottom layer (Sr-PH/Sr-R/Sr-P) could achieve a minimum RL of – 12 dB and an effective absorption bandwidth (EAB) value of 2.95 GHz. The microwave absorption performance was significantly increased with an increase of 0.5 mm in the total thickness of the tri-layer absorbers. In detail, the Sr-PH-0.5/Sr-R-1.5/Sr-P-0.5 absorber achieved the best values of RL and EAB at – 20 dB (illustrating 99% of the microwave incident wave being absorbed) and 4 GHz (covering 95% of the width of the X band frequency), respectively. The results indicated that the microwave absorption performance of SrM could improve by mixing up its different morphologies types.
Lightweight, high-strength electromagnetic(EM) absorption materials are in pressing requirement in both military and civilian fields. Porous silicon carbide (SiC) has attracted increasing attention as an EM absorption material. However, it’s absorption performance is still limited. In this work, the SiC foam/FeSiCr composites were prepared by a simple sacrificial template method coupled with an immersion process. FeSiCr particles were anchored on the three-dimensional porous SiC skeletons with polyurethane resin serving as a binder. Benefiting from the multiscale synergistic effect and coating strengthening efficacy, the obtained SiC foam/FeSiCr hybrids exhibited excellent EM absorption properties and high mechanical strength. Especially, the SiC foam/FeSiCr-40 sample possessed the best EM absorption ability with a minimum reflection loss (RLmin) value of -31.2 dB at 4.3 GHz at a thickness of 5 mm. Meanwhile, it also had a relatively high compressive strength of 5.62 MPa which was superior to that of the pure SiC foam (3.25 MPa). Moreover, the SiC foam/FeSiCr composites exhibited preferable salt spray corrosion resistance properties due to the chemical inertness of SiC and FeSiCr particles. Due to their excellent overall performance, SiC foam/FeSiCr composites have a great potential for application as structural absorption materials in ocean environments with high salt fog atmosphere. In addition, this work also provides guidance regarding the design and preparation of other structural absorption materials.
Nanotechnology, when this word comes in mind, it gives deep thought of new development in communication, medical science, intelligent transport system and many more. Ferrites nanoparticles have great significance owing to their amazing chemical and physical properties. In modern era we are developing materials for microwave applications and communication devices. Before the discovery of semiconductor memory chips, ferrites were the major form for electronic memory used in computers. Scientist have been studying and working with nanoparticles in magnetically guided drug delivery. The reactivity of material increases by the use of nanoparticles of that material. The dielectric characteristics of ferrites lean on diverse factors for instance methods of preparations and chemical composition. In various studies it has been found that their conductivity has dependence on temperature, composition and frequency. Among the various kinds of ferrites, Ni–Zn ferrites are viewed as the most adaptable ferrites as a result of their novel characteristics for applications at high frequency. The Ni-Zn ferrites are exploited as core materials in a variety of EM devices as well as have broad range of industrial applications e.g. inductors, microwave devices, power supplies, high and low frequency transformer cores, electromagnetic interference (EMI) suppressions and antenna rods. These broad ranges of applications are owing to their high resistivity, low eddy currents, high saturation magnetization, chemical stability and high Curie temperature. In view of this, the present chapter deals with the research progress on nickel-zinc ferrites in the bulk as well as nano size.
We intend to report on possible fabrication routes for all types of hexagonal ferrites which are known for their wide area of use and applications. Hexagonal ferrites have now become an intense topic of research as they are the part of most of magnetic recording and data storage applications globally. Hexagonal or popularly known as ‘Heaxa-ferrites’ are known for their utilization in permanent magnets and their utilization in electrical devices being operated at high frequencies especially at GHz frequencies. We have presented in this chapter all main six types of hexagonal ferrites i.e. M Type, Z-Type, Y-type, W-type, X-Type and U-type hexa-ferrites. Hexaferrites belong to ferromagnetic class of magnetic materials and their properties are purely dependent on intrinsic structure of ferrites. In this chapter, we aim to discuss more on M-type of hexa-ferrites, their properties and their applications. Also, recent advances on M-type ferrites are also a part of this chapter.
The gadolinium substituted cobalt ferrite (CoFe1.9Gd0.1O4) nanoparticles and CoFe1.9Gd0.1O4/Polyaniline (PANI) microwave absorber were synthesized by sol-gel auto combustion technique using lemon juice and in-situ polymerization method respectively. X-ray patterns confirmed the formation of single phase cubic structure. The crystallite size of the synthesized CoFe1.9Gd0.1O4 nanoparticles are within the range of 15–68 nm. The saturation magnetization of CoFe1.9Gd0.1O4 ferrite/Polyaniline (PANI) composite was reduced due to nonmagnetic PANI. The reflection loss for microwave absorbing properties of CoFe1.9Gd0.1O4 ferrite nanoparticles and CoFe1.9Gd0.1O4/PANI nanocomposite were investigated and minimum value of reflection loss was found to be −16.85 dB at 13.52 GHz for nanoparticles of thickness 2.5 mm and −25.59 dB at 11.92 GHz for CoFe1.9Gd0.1O4/PANI nanocomposite of thickness 2.0 mm) respectively. The prepared samples have low density, high surface resistivity and enhanced attenuation constant. The nanocomposite exhibits excellent absorption performance over a broad band range in the radar band.
The effect of the addition of bio-waste derived activated carbon (AC) on magnetic and dielectric properties of barium hexaferrite (BaFe12O19) has been investigated for microwave absorption application. Activated carbon was synthesized from banana peel while the low-density barium hexaferrite was fabricated by using the auto-combustion method. The composites consisting of highly conducting activated carbon and magnetic barium hexaferrite were prepared by using the low-cost ball-milling method. The addition of activated carbon in the ferrite matrix resulted in increased reflection loss due to interfacial polarization. The dielectric permittivity and dielectric loss tangent of BaFe12O19 showed a gradual increase with addition of AC. The magneto-crystalline anisotropy is however reduced with AC addition which resulted in decreasing values of saturation magnetization and magnetic loss tangent. The impedance matching, attenuation constant and reflection loss of the composites were calculated to determine their microwave absorption. The composite comprising of 40% BaFe12O19 and 60% AC showed the maximum reflection loss of -35.5 dB in X-band for coating thickness 1.3 mm. The 90% microwave absorption of the composite was achieved in the frequency range from 9.8 to 11.8 GHz. The results showed that the microwave absorption property of BaFe12O19 can be tuned in X-band by the addition of activated carbon.
The present research has been focused on the evaluations of microwave absorption characteristics of three-layer absorber with the approach of thickness optimization. Enhancement in microwave absorption feature predominantly depend on different factors such as multiple internal reflections between layers, interfacial polarization, phase cancellations, conduction loss, shape anisotropy and so on. By inspiring of these factors SrFe12O19, SiO2@SrFe12O19 and [email protected]12O19 nanocomposites were synthesized via tartrate-gel, stober and sol-gel methods respectively. XRD, FESEM, VSM and VNA techniques were used to determine the structural, microstructural, magnetic and microwave absorption features. The microwave absorption behavior of combination of these compounds with different layer arrangement and thickness were optimized via CST studio software. The maximum RL is reached to -42 dB at 9.5 GHz with 4.2 GHz effective bandwidth which composed of three distinct resonance peaks at 9.5, 10.5 and 11.5 GHz. It is expected that the three-layer absorbers with this arrangement is the excellent absorbers for X-band absorption applications.
Mg–Ti substituted barium hexaferrite (BaMg0.6Ti0.6Fe10.8O19) nanoparticles prepared by using steel millscale waste have been investigated towards the structural, magnetic and microwave properties. The samples were prepared using high-energy ball milling technique with the hematite (Fe2O3) as the raw utilized and processed from millscale waste product. The peaks with a single phase hexagonal structure of BaMg0.6Ti0.6Fe10.8O19 are identified at 1000 °C revealed from X-ray diffraction analysis. Higher saturation magnetization, Ms, with high crystallinity was observed in the sample due to the enhancement of superexchange interaction within the sample. The best maximum reflection loss of − 22.59 dB at the frequency and bandwidth of 9.42 GHz and 0.14 GHz was achieved in sample sintered at 1000 °C.
Ce–Co substituted, barium hexaferrite with the chemical composition of Ba0.5Ce0.5Fe11CoO19 was prepared by using the ceramic technique. The structural properties of the Ce–Co substituted, barium hexaferrite was investigated using X-ray diffractometer. The magnetic hysteresis loop of the sample was characterized by vibrating sample magnetometry. In order to identify the surface morphology of the sample, field emission scanning electron microscopy was used. Using the transmission/reflection coaxial line method in the range of 2–18 GHz, the complex permeability and complex permittivity, the reflection loss (RL) properties, absorption loss and shielding effectiveness of the prepared composition were determined. The maximum RL value of − 31.4 dB at 11.4 GHz with a 3 mm thickness sample was obtained and the maximum shielding effectiveness value was observed around 59.2 dB.
The shell on the nano-magnetic absorber can prevent oxidation, which is very important for its practical utilization. Generally, the nonmagnetic shell will decrease the integral magnetic loss and thus weaken the electromagnetic absorption. However, maintaining the original absorption properties of the magnetic core is a major challenge. Here, we designed novel and facile CoxFey@C composites by reducing CoxFe3-xO4@phenolic resin (x = 1, 0.5 and 0.25). High saturation magnetization value (Ms) of CoxFey particle, as a core, shows the interesting magnetic loss ability. Meanwhile, the carbon shell may increase the integral dielectric loss. The resulting composite shows excellent electromagnetic absorption properties. For example, at a coating thickness of 2 mm, the RLmin value can reach to -23 dB with an effective frequency range of 7 GHz (11-18 GHz). The mechanisms of the improved microwave absorption properties are discussed.
Since their discovery in the 1950s there has been an increasing degree of interest in the hexagonal ferrites, also know as hexaferrites, which is still growing exponentially today. These have become massively important materials commercially and technologically, accounting for the bulk of the total magnetic materials manufactured globally, and they have a multitude of uses and applications. As well as their use as permanent magnets, common applications are as magnetic recording and data storage materials, and as components in electrical devices, particularly those operating at microwave/GHz frequencies. The important members of the hexaferrite family are shown below, where Me = a small 2+ ion such as cobalt, nickel or zinc, and Ba can be substituted by Sr:
BaFe12O19 (BaM) has wide applications in electronic devices in the microwave frequency band. Ion doping has become a popular method to improve the performance of BaM in microwave absorption. This work investigates the microwave absorption properties of Ba(CoZr)xFe12-2xO19 (BFCZO-x, x = 0.2, 0.4, 0.6) ceramics prepared by the traditional solid-state reaction method. The structure and morphology confirm that BFCZO-x ceramics belong to the hexagonal system. The values of Ms (Hc) vary from 28 emu/g (828 Oe) to 40 emu/g (453 Oe) with the increase in x from 0.2 to 0.6, respectively. The microwave absorption results show that the maximum reflection loss can reach about −28.7 dB at 16.4 GHz of BFCZO-0.4 and present a broad bandwidth (13.34–18.8 GHz over −10 dB) with a thickness of 1.7 mm. Compared with other BaM-based materials, the coexistence of broad bandwidth and strong absorption in BFCZO-x ceramics indicates that it could be a promising material for designing microwave devices.
Ce-Nd-substituted M-type strontium hexaferrite nanoparticles, Sr(CeNd)x/2Fe12-xO19 (SCNH)(x = 0, 0.5, 1, 1.5, 2) can be successfully synthesized using co-precipitation method. The synthesized nanocomposites are characterized by X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscope (FESEM), vibrating sample magnetometer (VSM). The vector network analyzer (VNA) were used to analyze microwave absorption property. For comparison, the microwave absorption properties of the samples were measured by two simulation and metal back methods. The XRD and FT-IR analysis confirmed the existence of the M-type strontium hexaferrite phase in all samples. FESEM shows that the morphology of the particle in all of the samples was roughly hexagonal shape and they had uniform distribution. The VSM results indicated that increasing amounts of doped Ce³⁺ and Nd³⁺ reduced saturation magnetization (Ms) and coercivity (Hc). The minimum Hc for Sr (CeNd)x/2 Fe12-xO19 (SCNH) (x = 0, 0.5, 1, 1.5, 2) was 2700 Oe. The VNA results showed that by measuring the permittivity and permeability at 5 mm thickness and simulating the RL for <5 mm thicknesses the maximum RL would be obtained as −8.7 dB at d = 2.5 mm and f = 11 GHz in X = 2 sample. While using the metal back approach by direct measurement of RL from S11 at d = 2.5 mm thickness, results in maximum reflection loss of −37 dB at 9.62 GHz with 1.93 GHz bandwidth in X = 2 sample. This could be attributed to microstructural non-uniformities, which have not been taken into account in RL simulating method, while the direct calculation of RL at each specific thickness (by measuring the S11) yields more realistic results. Totally the results showed that Ce–Nd doped strontium hexaferrite nanoparticles are suitable candidates as microwave absorbers.
BaFe 12-x Co x O 19 (BFCO, x ≤ 0.4) ceramics with superior magnetic and electromagnetic (EM) properties were prepared using Co ³⁺ substituted BaFe 12 O 19 (BFO) in 2.6–18 GHz. Compared with the ceramics without Co ³⁺ , the incorporation of 40 mol% Co ³⁺ enhances magnetic properties; the saturation magnetization (M S ) is improved by about 55.6 emu·g ⁻¹ due to the variety of magnetocrystalline anisotropy. The resonance behaviors of complex permeability are observed and resonance frequency shifts to lower frequency range from 6 to 3 GHz. The minimum reflection loss (RL) of −32.1 dB (<−10 dB) is obtained at 11.2 GHz in 8.5–13.5 GHz at 2.0 mm thickness in the sample with x = 0.4, which suggests that such ceramics is highly promising as effective microwave absorbers for EM applications.
BaFe12O19 and BaFe11.5Ti0.5O19 were prepared by three-step calcination method. Phase analysis and microstructural study were carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Site occupancy of Ti⁴⁺ ions with calcination step were investigated by Fourier-transform infrared (FTIR) and Raman spectroscopy. The magnetic and microwave properties (Ku-band) were measured by vibration sample magnetometer and vector network analyzer. XRD patterns confirmed the hexaferrite phase formation in all samples. FTIR showed the presence of Ti⁴⁺ ions at spin down octahedral and tetrahedral sites. The peak shift in FTIR and Raman spectra suggested that ion occupancy increases with calcination step. A drastic decrease in the coercivity was observed with substitution. Low dielectric and magnetic losses in were observed in Ti– substituted samples. SEM revealed that Ti– substitution promotes hexagonal grain with decreased size. Overall microwave absorbance was greatly improved by three step calcination method.
La-Na co-substituted M-type Co-Ti-Mn barium hexaferrites Ba(1−2x)LaxNaxFe10Co0.5TiMn0.5O19 (0.00≤x≤0.25) were synthesized by conventional solid-state method. The influence of La-Na doping on the magnetic properties was investigated through VSM (vibrating sample magnetometer). The room temperature hysteresis loops show that the saturation magnetization decreases from 55.667 emu/g for x=0.00 to 44.768 emu/g for x=0.25 sample. To determine the complex permittivity (εr =ε′ – iε″) and permeability (µr =µ′ – iµ″) in 18.0–26.5 GHz frequency range, a vector network analyzer was employed. Reflection loss (RL) values were simulated from the values of εr and µr acquired using transmission line theory. The minimum RL obtained for the sample x=0.10 is −45.94 dB (99.997% signal absorption) with an absorption bandwidth of 8.33 GHz for 1.3 mm sample thickness. Thus, the synthesized hexaferrites can be utilised in electromagnetic shielding and radar stealth technology applications.
Layered microwave absorbing structures (MASs) for the suppression of electromagnetic signals are important due to their broadband frequency response. However, optimization of such structures is difficult because several design variables are involved. A method for the efficient design of broadband, layered, magneto-dielectric MASs is based on analytical modeling of the frequency-dependent complex dielectric permittivity (ε
r
) and magnetic permeability (μ
r
). The use of an efficient, extended Jaya's algorithm for optimization results in highly feasible values of ε
r
and μ
r
based on optimal Debye parameters for a specific reflection loss (RL) and a -10 dB absorption bandwidth. The optimization is carried out in the X-band for both singleand dual-layer MASs. Deeper insight is obtained by optimizing RL with and without constraints on absorber layer coating thickness. The results show the effectiveness of the optimization for the design of MASs for practical applications.
Gd, Mn and Co substituted barium hexagonal ferrite nanoparticles, according to the formula Ba1−xGdxFe12−2y(MnCo)yO19 and the proportion of (and x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1), have been prepared by hydrothermal method. Structural, magnetic and absorption microwave properties of the compositions were evaluated by x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), vibrating sample magnetometry, and vector network analysis. Studying the XRDs data showed the single-phase structure of all samples without any impurities at 900°C calcination temperature. FE-SEM micrographs demonstrated that the morphology of the nanoparticles has planar and nearly hexagonal morphology. The nanoparticles size calculated within the range of 62–85 nm. Study of the room temperature hysteresis loops of calcined samples indicated that maximum magnetizations and coercivities decreased compared to undoped composite with respect to x. The alterations of magnetizations and coercivities are related to the site occupation of substituted ions, change in grain growth inhibition and the effect of spin canting. Moreover, the results of microwave absorption measurements demonstrated that the maximum reflection loss of substituted Ba-hexaferrite equivalent to − 47 dB in sample x = 0.5 with thickness 5.6 mm at a frequency about 17.2 GHz and a bandwidth of 2 GHz greater than − 10 dB. The results showed that Gd has good potential for use as a rare-earth substitution in permanent magnet hexaferrites and these composites can be employed as absorbers in the gigahertz frequency range.
A co-precipitation method was employed to prepare M-type barium hexaferrite nanoparticles (BaCuxMgxZr2xFe12−4xO19) with different substitutions (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5). Then, their structural, magnetic and microwave properties were reported. These characteristics were investigated using various instruments including thermal analysis (TGA/DSC), X-ray diffraction (XRD) by the FULLPROF program, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA). In accordance with the FESEM graphs, the average particle sizes become smaller as the amounts of dopants increase. The VSM analysis proved that by increasing copper, magnesium and zirconium substitutions, the saturation magnetization, coercivity and remanence values are decreased. With an increase in the concentration of Cu-Mg-Zr ions, a monotonic decrease in coercivity, ranging from 4420.2 G to 161.64 G, was also observed. By increasing dopant ions from x = 0.0 to x = 0.5, the Curie temperature decreases from 467.2 °C to 230.46 °C. The relationship between reflection loss and frequency was evaluated theoretically for different thickness levels. Also, the resonance frequency shifts to lower frequencies by increasing Cu-Mg-Zr dopants due to the reduction of anisotropy field. According to microwave properties, BaCu0.5Mg0.5ZrFe10O19 sample could be counted as a single layer attenuator materials candidate for microwaves applications in the 2–18 GHz frequency range.
Core-shell composites, Fe3O4@C, with 500 nm Fe3O4 microspheres as cores have been successfully prepared through in situ polymerization of phenolic resin on the Fe3O4 surface and subsequent high-temperature carbonization. The thickness of carbon shell, from 20 nm to 70 nm, can be well controlled by modulating the weight ratio of resorcinol and Fe3O4 microspheres. Carbothermic reduction has not been triggered at present conditions, thus the crystalline phase and magnetic property of Fe3O4 micropsheres can be well preserved during the carbonization process. Although carbon shells display amorphous nature, Raman spectra reveal that the presence of Fe3O4 micropsheres can promote their graphitization degree to a certain extent. Coating Fe3O4 microspheres with carbon shells will not only increase the complex permittivity but also improve characteristic impedance, thus the microwave absorption properties of these composites are greatly enhanced. Very interestingly, a critical thickness of carbon shells leads to an unusual dielectric behavior of the core-shell structure, which endows these composites with strong reflection loss, especially in the high frequency range. By considering good chemical homogeneity and microwave absorption, we believe the as-fabricated Fe3O4@C composites can be promising candidates as highly effective microwave absorbers.
The magnetic, crystallographic properties and grain morphology of synthesized Ba0.5Sr0.5CoxTixFe(12 − 2x)O19 ferrite have been investigated by XRD, SEM and VSM. XRD and SEM confirm M-type hexagonal crystal structure. X-ray diffraction indicates expansion of hexagonal unit cell with substitution of Co2+ and Ti4+ ions. The microstructure governs increase in density and intergrain connectivity with substitution. The preferential site occupancy of substituted Co2+ and Ti4+ ions results in rapid decline of anisotropy field, hysteresis loops also revealed same effect of substitution. Coercivity and remanence magnetization can be easily controlled by varying substitution while maintaining high saturation magnetization, making it useful for recording media.
BaFe11.6−2xMxTixO19 (M=Co2+, Zn2+, Sn2+) compounds in powder form were prepared by a sol–gel route. The materials were annealed at several temperatures and characterised. The results showed that the cationic substitutions (x) lowered the coercivity (Hci), presumably due to the decrease of the magnetocrystalline anisotropy of the doped Ba ferrites. Sn–Ti mixtures decreased Hci faster than Zn–Ti and Ti–Co; however, lower magnetisations were achieved. In this regard, BaMZn–Ti showed slightly higher magnetisation than BaMTi–Co compounds. The effect of the heat-treatment temperature was to increase the magnetisation, following a slight coercivity decrease due to grain coarsening.
The impedance spectroscopy analysis for M-type BaFe12O19 (BaM) ceramics prepared by ceramic route is reported. The main aim is to investigate the electric properties in function of the synthesis parameters (milling time and milling power). It was shown that milling parameters strongly influence the electrical properties such as dielectric constant, whose magnitude increases with the milling power. Moreover the relaxation frequency is fully dependent on the milling parameters and it shifts to high frequencies when milling power decreases. Finally, impedance and dielectric loss tangent also change with milling parameters.
The effect of Mn2+Co2+Zr4+ substitution on complex permeability, permittivity and microwave absorption has been studied for BaFe12−x(Mn0.5Co0.5Zr)x/2O19 ferrite–polyvinylchloride (PVC) composites, where x varies from 0 to 3 in steps of 1, in frequency range from 15 to 20GHz. X-ray diffraction (XRD), scanning electron microscope (SEM), ac susceptometer, vibrating sample magnetometer, and vector network analyzer were used to analyze the structures, electromagnetic and microwave absorption properties. The results showed that, the magnetoplumbite structures for all samples have been formed. The samples having higher magnetic susceptibility and coercivity exhibit a larger microwave absorbing ability. Based on microwave measurement on reflectivity, BaFe12−x(Mn0.5Co0.5Zr)x/2O19 may be a good candidate for electromagnetic compatibility and other practical applications at high frequency.
Recent improvements performed on hard ferrite magnets with the Sr1−xLaxFe12−yCoyO19 composition are presented. The influence of the composition on both structural and magnetic properties of samples with y=x and y/x=0.75 is emphasized. Our investigations have allowed to optimize the permanent magnet properties of La–Co substituted hard ferrite magnets. The optimum composition contains more lanthanum than cobalt at the benefit of both lower irreversible losses and lower raw material costs.
X-ray structure investigations of ternary BaO–Ga2O3crystals grown in a Bi2O3flux led to discovery of a quaternary compound of ideal composition Ba2BiGa11O20. Single-crystal X-ray diffraction indicates a monoclinic unit cell with parametersa=14.9283(14) Å,b=11.7046(8) Å,c=5.1170(5) Å, andβ=91.137(7)°. The structure is similar to that of Ba3TiAl10O20and related compounds. Three different refinement trials were completed, involving different treatments of positioning of bismuth or gallium atoms shifted from normal barium and gallium sites. The refinement selected as representing the best model has only one bismuth atom positioned near a barium site at a displacement of 0.495 Å. A crystal chemical analysis based on the X-ray data suggests that the displacement of bismuth atoms is due to the stereochemical activity of the 6s2lone pair. X-ray refinement was carried out by full-matrix least squares onF2on all data, to giveR1=0.0689 andwR2=0.1802 for 104 parameters and 1361 independent reflections. The final position assignments were analyzed via bond valence sum calculations. Other crystal data:M=1570.58, space groupI2/m(No. 12),V=893.92(14) Å3,Z=2,Dc=5.835 g cm−3, MoKα=0.71073 Å,μ=30.506 mm−1, 2θmax=59.98°.
Single-crystal X-ray analysis has verified preparation of an ideal magnetoplumbite-type phase in the ternary barium hexagallate system. X-ray refinement was carried out by the full-matrix least-squares onF2method, to giveR1=4.61% and wR2=7.76% for 54 parameters and 374 independent reflections withI>2σ(I). Microanalysis data yields a composition of Ba1.07Ga11.95O19. The crystal chemistries of the barium hexagallate and barium hexaaluminate systems are compared and discussed. Crystal data for BaGa12O19:M=1277.98, space groupP63/mmc(No. 194),a=5.8140(8) Å,c=23.038(5) Å,V=674.4(2) Å3,Z=2,Dc=6.293 g cm−3, MoKα,λ=0.71073 Å,μ=26.532 mm−1, 2θmax=56.74°.
The application of the law of approach to saturation (LAS) to a great variety of ferromagnetic materials gives as a result a general correlation between the inhomogeneity parameter A and the anisotropy field HA, of the form HA = An (n ~ 1.4). Deviations of the data from this correlation are explained in terms of the metallurgical state of the material. The application of the LAS to mixed crystal series gives the concentration dependence of A(x) and HA(x). Unusually high HA values are explained by taking into account spin freezing effects. The increase of A(x) and HA(x) on approaching a critical concentration supports the appearance of mictomagnetism.
Microwave absorbing characteristics of carbonyl iron/epoxy resin composite with various volume concentrations were investigated in 0.1–18GHz. According to the electromagnetic parameters and thicknesses of the sample, numerical calculation and experiment have demonstrated that the frequency dependence of the microwave absorption comply with the quarter-wavelength (λ/4) matching model that may explain not only the peak frequency but also the number of the peaks. It implies that the quarter-wavelength condition can be successfully applied to understand and predict the peak frequency of the microwave absorption for ferromagnetic metal-based composites.
Lanthanum doped W-type hexaferrites BaZn2LaxFe16−xO27 (x=0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized by co-precipitation and sintered at 1320°C. The X-ray diffraction reveals W-type hexagonal structure with few traces of secondary phase. The decrease in grain size as a function of La-concentration is attributed to the fact that La acts as a grain inhibitor. The saturation magnetization and remanance decrease due to spin canting on B-sites. The increase in coercivity follows 1/r behavior where r is the radius of grain. The DC resistivity was observed to increase from 0.59×107 to 8.42×107Ωcm with increasing La-contents due to the unavailability of Fe3+ ions. This enhancement in resistivity makes these materials promising candidates for use at high frequencies in order to reduce eddy current losses.
The possibility of replacing Sr by La and Fe by Co and the subsequent improvement of the magnetic properties of the M-type ferrite stimulated our interest in studying other rare-earth ion substitutions. We have found that Sm and Nd substitutions can increase the coercivity of the hydrothermally synthesised Sr hexaferrite powder without causing any significant fall in the saturation magnetisation. In the present work, La-substituted Sr hexaferrite particles were prepared by hydrothermal synthesis and subsequent calcinations. The effects of the initial La/Sr ratio and the calcination temperature on the structure, particle morphology and magnetic properties of La-substituted Sr hexaferrite were investigated by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometry and a pulsed field magnetometer. It was found that, under hydrothermal conditions, the La3+ additives did not substitute exclusively into the SrM structure but this could be achieved to a greater extent by subsequent calcinations at high temperatures. Compared to the effect of Sm and Nd substitutions, La substitution only increases slightly the coercivity for the samples with initial La/Sr ratios up to 1/8, and for the samples with La/Sr ratios such as 1/4 and 1/2, the coercivity is smaller than that of the sample without La. This can be attributed to grain growth during calcination. Most of the La-substituted samples exhibit a similar magnetisation to that of SrFe12O19.
Significant improvements of the magnetic properties of M-type hexaferrites (SrFe12O19) can be achieved through partial substitutions with a rare-earth element and a transition metal. From this point of view, 57Fe Mössbauer spectrometry is a very powerful tool to determine the location of the substituted elements. We discuss here the effects on the Mössbauer spectrum of the substitution of a rare earth ion (Sm3+, Nd3+ or La3+) in the Sr2+ site, and the substitution of a metal ion (Co2+ or Zn2+) in the Fe3+ sites.
The magnetic and electrical behavior of SrZrxCuxFe12−2xO19 (where x=0.0–0.8) hexaferrite nanoparticles are reported in this paper. Five samples were synthesized by the chemical co-precipitation method. SrFe12O19 is a semiconductor however doping ZrxCux at iron sites resulted in a semiconductor-metal transition at a temperature TM–S. The structural parameters of the samples were obtained by FTIR, XRD, EDX, SEM and TEM analyses. The FTIR spectrum and XRD pattern of the samples showed that the synthesized materials were of a single phase. The particle size was in the range 26–37nm as estimated by Scherrer formula, which is comparable with the values estimated from SEM (40–80nm) and TEM (30–60nm) analyses. AC magnetic susceptibility and DC electrical resistivity measurements were carried out in a temperature range 300–800K. The Curie temperature (TC) decreases on substitution of Zr–Cu. A significant increase in the room temperature resistivity is noted with the addition of Zr–Cu up to x≤0.4. The drift mobility (μd) and the activation energy (ΔE) are also calculated from electrical resistivity data. The variation of the dielectric constant (ɛ′) and the dielectric loss factor (tanδ) with frequency in the range 80Hz–1MHz and composition of the sample is observed.
The electromagnetic (EM) and microwave absorption properties of ( Co 2+– Si 4+) substituted barium hexaferrite compositions Ba Co x 2+ Fe y +2 Si x+y 4+ Fe 12-2x-2y +3 O 19 ( x=0.9 and y=0.0 , 0.05, and 0.2) and its polymer composites prepared from hexaferrite, polyaniline, and carbon powders dispersed in polyurethane matrix have been investigated at the microwave frequency range of the X band (8.2–12.4 GHz ) . The hexaferrite compositions were synthesized by solid-state reaction technique, whereas polyaniline, by chemical route. The permeabilities of a ferrite are drastically reduced at higher gigahertz frequencies. The permittivities, however, can be enhanced by appropriate choice of composition and processing temperature. In the present ferrite composition, silicon content is taken in excess so as to convert some of the Fe 3+ ions to Fe 2+ ions. This conversion has been shown to enhance EM and absorption properties. Mössbauer spectroscopy on the samples establishes that addition of excess Si 4+ converts some of the Fe 3+ to Fe 2+ . The sintered ferrites have shown resonance phenomena, but the composites do not. The EM parameters ε′ , ε″ , μ′ , and μ″ were measured using a vector network analyzer (Agilent-
, model PNA E8364B). These measured EM parameters were used to determine the absorption spectra at different sample thicknesses based on a model of a single layered plane wave absorber backed by a perfect conductor. The sintered ferrite composition ( x=0.9 and y=0.05 ) showed the best absorption properties [a minimum reflection loss of -17.7 to -14.3 dB over the whole frequency range of the X band (8.2–12.4) for a sample thickness of just 0.8 mm ], and it is used in the composite absorbers in powder form along with other constituents. The optimized composite absorber has shown dielectric constant ε′∼11.5 , dielectric loss ε″∼2.3 , and a minimum reflection loss of -29 dB at 10.97 GHz with the -20 dB bandwidth over the frequency range of 9.7–12.2 GHz for a sample thickness of 2.0 mm . The magnetic parameters μ′ and μ″ for the composite remained nearly 1 and 0, respectively, throughout the measured frequency range. Both sintered ferrite and composite absorbers can fruitfully be utilized for suppression of electromagnetic interference and reduction of radar signatures (stealth technology).
In the study, the Ni–Zn ferrite powder of a Ni0.3Zn0.7Fe2O4 composition was synthesized by sol–gel route using metal acetates at low temperatures. Both the scanning electron microscope and X-ray diffraction analyses of various gel samples heated at different temperatures were used to identify the reaction stages where the amorphous-gel-to-crystalline phase transition occurred. The electrical, magnetic and microstructural properties of the toroidal cores were studied. It was found that the initial permeability increased with a large frequency band (0.1–31.39 MHz) and the magnetic loss was small. The electrical resistivity was higher as compared to the ones which were obtained by the conventional process. Therefore, well–defined polycrystalline microstructure nickel–zinc ferrite and a short processing time of gel preparation have become the major achievements of this study.
Co 50/( SiO 2)50 nanoparticles were synthesized by a wet chemical method, and their microwave permeability was measured in the 0.1–18 GHz range. The synthesized nanoparticles exhibit two loss peaks at microwave frequencies: one appears around 7.0 GHz and is believed to result from the eddy current effect, the other appears around 250 MHz and is probably caused by natural ferromagnetic resonance. Compared with micrometer-size Co particles, the synthesized nanoparticles exhibit high permeability μ′ and low magnetic loss, especially over 10–18 GHz. © 2002 American Institute of Physics.
Single-layer absorbers composed of sintered planar hexagonal
ferrites were developed. The absorbers have 50~90% relative bandwidth at
microwave frequencies. The broadband characteristics were successfully
analyzed by a quarter-wavelength resonator model, which took into
account both a wavelength reduction due to
1/√(εrμr) and a resonant frequency
shift depending on tan δμ, where εr
and μr are relative permittivity and permeability,
respectively, for the resonator material
The complex permittivity (ε′–jε″), complex permeability (μ′–jμ″) and microwave absorption properties of ferrite–polymer composites prepared with different ferrite ratios of 50%, 60%, 70% and 80% in polyurethane (PU) matrix have been investigated in X-band (8.2–12.4 GHz) frequency range. The M-type hexaferrite composition BaCo+20.9Fe+20.05Si+40.95Fe+310.1O19 was prepared by solid-state reaction technique, whereas commercial PU was used to prepare the composites. At higher GHz frequencies, ferrite's permeabilities are drastically reduced, however, the forced conversion of Fe+3 to Fe+2 ions that involves electron hopping, could have increased the dielectric losses in the chosen composition. We have measured complex permittivity and permeability using a vector network analyzer (HP/Agilent model PNA E8364B) and software module 85071. All the parameters ε′, ε″, μ′ and μ″ are found to increase with increased ferrite contents. Measured values of these parameters were used to determine the reflection loss at various sample thicknesses, based on a model of a single-layered plane wave absorber backed by a perfect conductor. The composite with 80% ferrite content has shown a minimum reflection loss of −24.5 dB (>99% power absorption) at 12 GHz with the −20 dB bandwidth over the extended frequency range of 11–13 GHz for an absorber thickness of 1.6 mm. The prepared composites can fruitfully be utilized for suppression of electromagnetic interference (EMI) and reduction of radar signatures (stealth technology).
Nanoparticles of nickel ferrite have been synthesized by the sol–gel method and the effect of grain size on its structural and magnetic properties have been studied in detail. X-ray diffraction (XRD) studies revealed that all the samples are single phasic possessing the inverse spinel structure. Grain size of the sol–gel synthesized powders has been determined from the XRD data and the strain graph. A grain size of 9 nm was observed for the as prepared powders of NiFe2O4 obtained through the sol–gel method. It was also observed that strain was induced during the firing process. Magnetization measurements have been carried out on all the samples prepared in the present series. It was found that the specific magnetization of the nanosized NiFe2O4 powders was lower than that of the corresponding coarse-grained counterparts and decreased with a decrease in grain size. The coercivity of the sol–gel synthesized NiFe2O4 nanoparticles attained a maximum value when the grain size was 15 nm and then decreased as the grain size was increased further.
Magnetic and microwave absorption properties of BaMg x/2 Mn x/2 Co x Ti 2x Fe 12-4x O 19 hexaferrite nanoparticles
- R S Alam
- M Moradi
- H Nikmanesh
- J Ventura
- M Rostami
R.S. Alam, M. Moradi, H. Nikmanesh, J. Ventura, M. Rostami, Magnetic and
microwave absorption properties of BaMg x/2 Mn x/2 Co x Ti 2x Fe 12-4x O 19 hexaferrite nanoparticles, J. Magn. Magn. Mater. 402 (2016) 20e27.