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.     

Role of exchange coupling between the hard and soft magnetic phases on the absorption of microwaves by SrFe10Al2O19/Co0.6Zn0.4Fe2O4 nanocomposite

(1-x)SrFe₁₀Al₂O₁₉/(x)Co_0.6Zn_0.4Fe₂O₄-(SFAO/CZFO) hard/soft nanocomposite ferrite materials were synthesized by ‘one-pot’ self-propagating combustion route. The co-existence of the two magnetic phases were confirmed by XRD, FESEM, EDS and VSM. The prepared nanocomposite samples were also characterized by TGA/DSC, Raman spectroscopy and VNA. Exchange coupling between the hard and the soft magnetic grains was observed by determining the switching field distribution (SFD) curve. As a result of the competing effects of exchange interaction and dipolar interaction, magnetic parameters were observed to be sensitive to the incorporation of soft magnetic phase into the nanocomposite. Results showed that with the inclusion of soft magnetic phase, exchange coupling behaviour between the hard and the soft ferrite phases had significant influence on the microwave absorption capacity of the samples. Related electromagnetic parameters and impedance matching ratio of the nanocomposite system were discussed. A minimum reflection loss of ?42.9 dB with an absorber thickness of 2.5 mm was attained by the nanocomposite (90 wt%)SrFe₁₀Al₂O₁₉/(10 wt %)Co_0.6Zn_0.4Fe₂O₄ at a matching frequency of 11.45 GHz. This assured the candidacy of SrFe₁₀Al₂O₁₉/Co_0.6Zn_0.4Fe₂O₄ nanocomposite as a promising microwave absorption material in the X-band (8–12 GHz).     

Enhanced High‐Frequency Properties of NiZn Ferrite Ceramic with Co2Z‐Hexaferrite Addition

Significantly enhanced dielectric and loss characteristics have been observed in Ni_0.4Zn_0.6Fe₂O₄ ferrite with various Ba₃Co₂Fe₂₄O₄₁ (Co₂Z) addition (x). Compared with pure NiZn and Co₂Z ferrites, the composite ceramics obtain much refined grains and notable high‐frequency characteristics. With the introduction of Co₂Z into NiZn ferrite matrix, the resistivity is largely increased from the order of 10⁶ Ω cm to the order of 10⁸ Ω cm and the frequency stability of permittivity is dramatically enhanced. Co₂Z addition obviously improves the magnetic quality factor Q and reduces the dielectric loss of the ceramics at high frequency. For the samples with x = 20?30 wt%, permittivity ε′ is almost unchanged from 1 MHz to 1 GHz, Q is greater than 10 in a wide frequency range, and dielectric loss tan δ_ε is observed to be of the order of 10^?3 at 100 MHz, which is lower by two orders of magnitude compared with pure NiZn and Co₂Z ferrites. These characteristics are all desirable for magneto‐dielectric ferrites in high‐frequency applications.     

Effects of Mg Substitution on Order/disorder Transition,Microstructure, and Microwave Dielectric Characteristics of Ba((Co0.6Zn0.4)1/3Nb2/3)O3 Complex Perovskite Ceramics

Effects of Mg substitution on order/disorder transition, microstructure, and microwave dielectric characteristics of Ba((Co_0.6Zn_0.4)_1/3Nb_2/3)O₃ complex perovskite ceramics have been investigated. The ordered complex perovskite solid solutions are obtained in Ba((Co_0.6?x/2Zn_0.4?x/2Mg_x)_1/3Nb_2/3)O₃ ceramics (x = 0, 0.1, 0.2, and 0.3), and the ordering degree in the as‐sintered dense ceramics increases with increasing Mg‐substitution amount. The significantly improved Qf value is obtained in the present ceramics with increasing x, whereas the dielectric constant decreases slightly together with some increase of temperature coefficient of resonant frequency. The best combination of microwave dielectric characteristics is obtained in the composition of x = 0.3: ε_r = 33.7, Qf = 93 800 GHz, and τ_f = 9.6 ppm/°C. In the Mg‐substituted compositions, clear domain boundaries are obtained and the domain size increases as x increases, the highest Qf value is obtained when the domain size is about 40–60 nm in the ceramics with x = 0.3. The increased ordering degree and the fine ordering domain structure are considered to primarily contribute to the significant increase of Qf value in the Mg‐substituted Ba((Co_0.6Zn_0.4)_1/3Nb_2/3)O₃ complex perovskite ceramics.     

Magnetic and antimicrobial properties of cobalt-zinc ferrite nanoparticles synthesized by citrate-gel method

The cobalt-zinc ferrite (CZF) nanomaterials were prepared by citrate-gel method, and further calcined at 600°C. The single-phase cubic spinel structure of CZF was confirmed using the X-ray diffraction pattern. The average crystallite size was found to be in the range of 22-29 nm. The surface morphology was examined using the scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The average particle size of Co_0.6Zn_0.4Fe₂O₄ was determined to be 19 nm using TEM study which is supporting the average crystallite size measured from the X-ray diffraction studies. The Fourier-transform infrared spectra revealed the two strong absorption bands in the series of ferrites between 4500 and 500 cm⁻¹ and these are responsible for the characteristic of spinel ferrites. The presence of elements Cu, Zn, and Co of CZF was confirmed by the elemental spectral signals of energy dispersive spectroscopy. At room temperature, the magnetic measurements of pure ZnFe₂O₄ and Co_0.6Zn_0.4Fe₂O₄ were evaluated based on hysteresis curves (M-H curves). The results expressed that the addition of nonmagnetic Zn²⁺ ions increases the magnetic behavior in the mixed CZF samples. The antimicrobial activity of the ZnFe₂O₄ and Co_0.6Zn_0.4Fe₂O₄ nanoferrites was tested against harmful microbes.     

Effects of Postdensification Annealing upon Microstructures and Microwave Dielectric Characteristics in Ba((Co0.6−x/2Zn0.4−x/2Mgx)1/3Nb2/3)O3 Ceramics

Effects of postdensification annealing upon microstructures and microwave dielectric characteristics in Ba((Co_0.6?x/2Zn_0.4?x/2Mg_x)_1/3Nb_2/3)O₃ (x = 0, 0.1, 0.2, and 0.3) complex perovskite ceramics have been investigated. Long‐time annealing at temperatures below the order–disorder transition temperature enhances the cation ordering degree and promotes the ordering domain growth. The most significant improvement of Qf value is obtained together with the suppressed temperature coefficient of resonant frequency in the samples annealed at 1400°C for 12 h, while the dielectric constant decreases slightly. The Qf value of ceramics annealed at 1400°C mainly attributes to the enhanced cation ordering degree, because their low‐energy domain boundaries are not detrimental to the Qf value. As the annealing temperature increases close to the transition temperature, coarse ordering domains with high‐energy boundaries are formed, and then the Qf value steadily decreases because of the inferior domain structure, even the cation ordering degree increases. The microwave dielectric characteristics of Ba((Co_0.6?x/2Zn_0.4?x/2Mg_x)_1/3Nb_2/3)O₃ ceramics are affected by the common function of ordering degree and domain structure. The best combination of microwave dielectric characteristics is obtained in the composition of x = 0.3 after annealing at 1400°C for 12 h: ε_r = 33.2, Qf = 117 200 GHz, and τ_f = 8.6 ppm/°C.     

Synthesis and Characteristics of Superparamagnetic Co0.6Zn0.4Fe2O4 Nanoparticles by a Modified Hydrothermal Method

Nanoparticles of Co_0.6Zn_0.4Fe₂O₄, with narrow size distribution, regular morphology, and high saturation magnetization, have been synthesized. The synthesis, involved a very rapid mixing of reducible metal cations with sodium borohydride, is carried out in a colloid mill and followed by a separate hydrothermal process. The microstructure and magnetic properties of the synthesized nanoparticles are characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The effects of different synthesis conditions (synthesis temperature and reaction time) on the characteristics of the ferrite nanoparticles are discussed. The changes in cation contribution are revealed by the Raman study. The magnetic measurements explore that all the as‐synthesized samples are superparamagnetic in nature. The corresponding superparamagnetic behavior is explained by paramagnetic Langevin theory. Note that, the superparamagnetic Co_0.6Zn_0.4Fe₂O₄ ferrite nanoparticle, with excellent performance, can be synthesized at 160°C for a short reaction time (4 h).     

Crystal structure and microwave dielectric properties of Li2Mg0.6− xCoxZn0.4SiO4 ceramic for LTCC applications

In this work, Li₂Mg_0.6−xCo_xZn_0.4SiO₄ ceramics (x = 0–0.4) added with 3 wt% Li₂O–B₂O₃–Bi₂O₃–SiO₂ (LBBS) glass were synthesised using the solid-state reaction method. The effects of substituting Co²⁺ for Mg²⁺in Li₂Mg_0.6−xCo_xZn_0.4SiO₄ ceramics on crystal structure, microstructure, densification, crystallisation and microwave dielectric properties were investigated. X-ray diffraction patterns showed that monoclinic Li₂MgSiO₄, monoclinic Li₂ZnSiO₄ and orthorhombic Li₂CoSiO₄ formed finite solid solution in Li₂Mg_0.6−xCo_xZn_0.4SiO₄ ceramics. Clear grain boundaries were observed via scanning electron microscopy. The substitution of Co²⁺ for Mg²⁺ increased grain size, densification, crystallinity degree and dielectric constant; it also reduced the dielectric loss of the ceramics to a certain extent. The absolute values of τ_f were positively related to the crystallinity degree. Li₂Mg_0.55Co_0.05Zn_0.4SiO₄ ceramic added with 3 wt% LBBS and sintered at 900 °C exhibited considerable microwave dielectric properties of ε_r = 5.8, Q × f = 47,518 GHz and τ_f = −74.8 ppm/°C. Therefore, the ceramic is considered a candidate low-temperature co-fired ceramic material for substrate and filter applications.     

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.     

Optimization of electromagnetic matching of Ba1-xCaxFe11.4Co0.6O19 (0.2 ≤ x ≤ 0.8) ceramics for microwave absorption within 2.6–18 GHz

The Ba_1-xCa_xFe_11.4Co_0.6O₁₉ (x = 0.0, 0.2, 0.4, 0.6, and 0.8) composites with wide-bandwidth and good absorption performance were prepared. The M_S of ceramics increases from about 62.4 to 83.4 emu g⁻¹ as x rises from 0 to 0.6, which demonstrates that the desirable magnetic properties of such ceramics is obtained by adjusting the content of Ca²⁺. A bandwidth of reflection loss (RL) below - 5 dB can be obtained for frequencies from 5.9 to 18 GHz with the Ba_0.4Ca_0.6Fe_11.4Co_0.6O₁₉ ceramic and a thickness of 2.0 mm, and a larger RL value of −34.1 dB is observed at 8.2 GHz for the Ba_0.6Ca_0.4Fe_11.4Co_0.6O₁₉ ceramic. These results suggest the developed ceramics could act as effective and wide-bandwidth microwave absorbing materials to meet commercial and military applications.     

Nano Ca–Mg–Zn ferrites as tuneable photocatalyst for UV light-induced degradation of rhodamine B dye and antimicrobial behavior for water purification

We report the synthesis of Ca-doped Mg–Zn ferrite Mg_0.4Zn_(0.6-x)Ca_xFe₂O₄ nanomaterials with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 through citrate precursor approach and their structural, morphological, optical, photocatalytic, and antimicrobial properties were systematically studied. The prepared nanoferrites's cubic spinel structure with an average crystallite size of 15–38 nm was evaluated by the XRD examination. The spherical morphology of these ferrite nanoparticles was seen from scanning electron microscopy (SEM). The observed bands at 560 cm⁻¹ and 406 cm⁻¹ in the FTIR spectra confirmed the spinel structure of the synthesized nanoferrite. The optical study confirmed an optical band gap of 1.60 eV–1.86 eV. The photocatalysis was done for the degradation of rhodamine B dye solution under UV light. All the synthesized nano ferrites displayed a promising antimicrobial potential upon Candida albicans fungi. Mg_0.4Zn_0.1Ca_0.5Fe₂O₄ nanoparticles have a better photocatalytic response (99.5%) for the degradation of rhodamine B dye and show superior antimicrobial activity (96.1%) for the inhibition of Candida albicans fungi.     

Structural,electrical and magnetic properties of Co0.5Zn0.5AlxFe2−xO4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) prepared via sol–gel route

Nanoparticles of Co_0.5Zn_0.5Al_xFe_2?xO₄ (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) were synthesized by sol–gel method and the influence of Al³⁺ doping on the properties of Co_0.5Zn_0.5Fe₂O₄ was studied. X-ray diffraction studies revealed the formation of single phase spinel type cubical structure having space group Fd-3m. A decreasing trend of the lattice parameter was observed with increasing Al³⁺ concentration due to the smaller ionic radii of Al³⁺ ion as compared to Fe³⁺ ion. TEM was used to characterize the microstructure of the samples and particle size determination, which exhibited the formation of spherical nanoparticles. The particle size was found to be increases up to ～45 nm after annealing the sample at 1000 °C. Electrical resistivity was found to increase with Al³⁺ doping, attributed to the decrease in the number of Fe²⁺–Fe³⁺ hopping. The activation energy decreased with increasing Al³⁺ ion concentration, indicating the blocking of conduction mechanism between Fe³⁺–Fe²⁺ ions. The value of saturation magnetization decreased, when Fe³⁺ ions were doped with Al³⁺ ions in Co_0.5Zn_0.5Fe₂O₄; however, the coercivity values increased with increasing Al³⁺ ion content.     

Optical and Microwave Dielectric Properties of Zn‐Doped MgAl2O4 Transparent Ceramics Fabricated by Spark Plasma Sintering

(Mg_1?xZn_x)Al₂O₄ transparent ceramics were fabricated by spark plasma sintering technique at 1325°C for 10 min. A small mount of Zn²⁺ addition to MgAl₂O₄ ceramics was very effective to the performance improvement, while further increase in Zn‐doped content would give rise to the optical transmittance deterioration. The optical and microwave dielectric properties of MgAl₂O₄ transparent ceramics were improved by Zn substitution for Mg. The in‐line transmittance of the (Mg_1?xZn_x)Al₂O₄ (x = 0.02) ceramics can be as high as 70% at λ = 550 nm and 86.5% at λ = 2000 nm, respectively. The dielectric constant ε_r of (Mg_1?xZn_x)Al₂O₄ just varied from 8.32 to 8.54, however, the Q × f value increased significantly up to a maximal value of 66,000 GHz at x = 0.02. Moreover, the τ_f of (Mg_1?xZn_x)Al₂O₄ transparent ceramics changed from ?74 to ?65.5 ppm/°C. With the increasing of Zn‐doped content, the average grain size and the porosity increased, which was the primary reason for the change in optical and microwave dielectric properties.     

Facile synthesis of Co0.5Zn0.5Fe2O4 nanoparticles decorated reduced graphene oxide hybrid nanocomposites with enhanced electromagnetic wave absorption properties

Herein, reduced graphene oxide/cobalt-zinc ferrite (RGO/Co_0.5Zn_0.5Fe₂O₄) hybrid nanocomposites were fabricated by a facile hydrothermal strategy. Results revealed that the contents of RGO could affect the micromorphology, electromagnetic parameters and electromagnetic wave absorption properties. As the contents of RGO increased in the as-synthesized hybrid nanocomposites, the dispersibility of the particles was improved. Meanwhile, numerously ferromagnetic Co_0.5Zn_0.5Fe₂O₄ particles were evenly anchored on the wrinkled surfaces of flaky RGO. Besides, the obtained hybrid nanocomposites exhibited superior electromagnetic absorption in both X and Ku bands, which was achieved by adjusting the RGO contents and matching thicknesses. Significantly, when the content of RGO was 7.4 wt%, the binary nanocomposites showed the optimal reflection loss of -73.9 dB at a thickness of 2.2 mm and broadest effective absorption bandwidth of 6.0 GHz (12.0–18.0 GHz) at a thin thickness of merely 2.0 mm. The enhanced electromagnetic absorption performance was primarily attributed to the multiple polarization effects, improved conduction loss caused by electron migration, and magnetic loss derived from ferromagnetic Co_0.5Zn_0.5Fe₂O₄ nanoparticles. Our results could provide inspiration for manufacturing graphene-based hybrid nanocomposites as high-efficient electromagnetic wave absorbers.     

Dielectric and gyromagnetic structure modulations of Zn–Sn codoped yttrium–iron–garnet based on the density-generalized functional theory and P–V–L bond theory

Herein, the crystal structure, dielectric properties, and gyromagnetic characteristics of Zn–Sn codoped Y₃Zn_xSn_xFe_5−2xO₁₂ (x = 0.0–0.5) prepared using a conventional ceramic process were investigated. According to the first-principles’ calculations and complex crystal bonding theory, Zn²⁺–Sn⁴⁺ codoping can increase the relative dielectric constant (ε_r) by enhancing the average ionicity. The x-ray photoelectron spectroscopy (XPS) and Raman analysis results indicate that an appropriate amount of Zn²⁺–Sn⁴⁺ codoping can help improve the microscopic morphology, maintain the appropriate ratio of divalent iron ions, and reduce the microwave magnetic and electrical losses of YIG ferrites. The optimized microwave properties are as follows. Y₃Zn_0.3Sn_0.3Fe_4.4O₁₂ after sintering at 1400°C; ε_r = 15.6; dielectric loss, that is, tanδ_ε = 4.3 × 10⁻⁴; saturation magnetization, that is, 4πM_S = 2244 G; ferromagnetic resonance linewidth, that is, ΔH = 37 Oe. These properties can help improve the performance of high-frequency microwave components by enhancing the properties of ferrite.     

Synthesis and analysis of structural,compositional, morphological,magnetic, electrical and surface charge properties of Zn-doped nickel ferrite nanoparticles

Zn-doped nickel ferrite nanoparticles (Zn_xNi_(1-x)Fe₂O₄) were synthesized using the co-precipitation technique. The structural and compositional studies of the Zn_xNi_(1-x)Fe₂O₄ nanoparticles revealed their face-centred cubic spinel structure and an appropriate amount of Zn doping in nickel ferrite nanoparticles, respectively. The morphological analysis had been carried out to obtain the particle size of the synthesized nanoparticles. The magnetic studies revealed the superparamagnetic nature of the Zn_xNi_(1-x)Fe₂O₄ nanoparticles, and the maximum magnetization of 30 emu/g for the Zn_0.2N_0.8Fe₂O₄ sample. The M ? H curves were fitted with the Langevin function to obtain the magnetic particle diameter of Zn_xNi_(1-x)Fe₂O₄ nanoparticles. The electrical conduction in Zn_xNi_(1-x)Fe₂O₄ nanoparticles was explained through the Verway hopping mechanism. The Zn_0.2N_0.8Fe₂O₄ nanoparticle exhibited a higher electrical conductivity of 42 μS/cm and surface charge of ?29/7 mV due to the enhanced hopping of Fe³⁺ ions in the octahedral sites. Owing to this nature, they were identified as the suitable candidates in the applications such as thermoelectrics, hyperthermia, magnetic coating and for the preparation of conducting ferrofluids.     

Structural,interfacial, magnetic and dielectric properties of (1−x)(Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4@xNi0.4Zn0.6Fe2O4 composite at high frequency

(Mg_0.95Zn_0.05)₂(Ti_0.8Sn_0.2)O₄ powder was synthesized by a solid state reaction. Then, Ni_0.4Zn_0.6Fe₂O₄ was grown on the (Mg_0.95Zn_0.05)(Ti_0.8Sn_0.2)O₄ particles in a hydrothermal environment to form a core-shell structure. (1-x)(Mg_0.95Zn_0.05)₂(Ti_0.8Sn_0.2)O₄@xNi_0.4Zn_0.6Fe₂O₄ composite ceramics were sintered at 1200 °C with these powders. XRD, SEM, TEM analyses indicated that high dense core-shell ceramics without any foreign phase were obtained. Different types of sharp interfaces were self-assembled owing to the minimization of direct elastic energy in the hydrothermal environment. The composites enjoy good magnetic and dielectric properties, especially, good microwave dielectric properties with high saturation magnetization when the ferrite content is 0.3–0.5. The results provided a powerful experimental basis for the sensor and transducer.     

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.     

Glass Additive Influence on the Sintering Behaviors,Magnetic and Electric Properties of Bi–Zn Co‐Doped Co2Y Ferrites

The Bi₂O₃–B₂O₃–ZnO–SiO₂ (BB35SZ) glass effects on the sintering behavior and magnetic properties of Bi–Zn co‐doped Co₂Y ferrites were investigated in developing low‐temperature‐fired ferrites. The results indicate that BB35SZ glass can be used as a sintering aid to reduce the densification temperature of Co₂Y ferrites from 1300°C to 900°C. The 2(Ba_0.9Bi_0.1O)·2(Zn_0.4Co_0.4Cu_0.2O)·6(Fe_1.97Zn_0.03O₃) ferrite with 4 wt% BB35SZ glass can be densified below 900°C, exhibiting an initial permeability of 3.4 and quality factor of 55. This process provides a promising candidate for multilayer chip magnetic devices for microwave applications.     

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.