Nb5+ ion substitution assisted the magnetic and gyromagnetic properties of NiCuZn ferrite for high frequency LTCC devices

Nowadays, developing nickle zinc ferrites with excellent magnetic and gyromagnetic properties are of great importance for solving the matching problem of 5G communication system. However, much is discussed about soft magnetic properties, but little is reported gyromagnetic properties that is critical for microwave device applications. Herein, Nb⁵⁺ ions substituted Ni_0.29Cu_0.18Zn_0.53Nb_xFe_2-xO₄ (x = 0.00-0.05), possessing high saturation magnetization, approriate initial permeability, high cut-off frequency and low ferromagnetic resonance linewidth (@9.55 GHz), were synthesized by low-temperature firing (900 °C). The phase structure and morphology evolutions were studied in detail. The results of morphology observations revealed that Nb⁵⁺ substitution has significant role in determining produce compact and uniform microstructures of NiCuZn ferrites via suppress the grain growth, which further corresponding enhance the magnetic and gyromagnetic properties. As a result, a uniform and compact grain size can be obtained, corresponding to the change of magnetic and gyromagenetic properties have different trends. Enhanced magnetic and gyromagnetic performance including high initial permeability (μ' = 203 @1 MHz), saturation magnetization (4πM_s = 3966 Gauss) and low ferromagnetic resonance linewidth (ΔH = 203 Oe) of the NiCuZn ferrites is achieved though adjusting Nb⁵⁺ ions substitution. More importantly, this work not only for low temperature co-fired ceramic (LTCC) technology but also for high frequency and microwave frequency devices including phase shifter and radars.     

Low temperature firing of Co2Y–NiCuZn ferrite composites

Hexagonal structure magnetoplumbite ferrites have revealed a higher dispersion frequency than that of nickel ferrites because of the magnetoplumbite's magnetic anisotropy. The magnetoplumbite ferrite densification temperature always exceeds 1000 °C and the initial low temperature firing permeability of magnetoplumbite ferrites with added glass is too low (μ_i = 2–4). Therefore, it is desirable to develop a material that has a higher permeability at above 300 MHz and can be densified at temperatures below 900 °C. The Bi₂O₃–B₂O₃–ZnO–SiO₂ (BBSZ) glass addition effects on the densification and magnetic properties of Co₂Y–NiCuZn ferrite composites with various Co₂Y/NiCuZn ferrite ratios were investigated. The densification of Co₂Y–NiCuZn ferrite composites was enhanced by the addition of glass at low sintering temperatures (<900 °C) due to the liquid phase sintering. Co₂Y–NiCuZn ferrite composites with 4 wt% BBSZ glass sintered at 900 °C show a relative density above 90%, a high-initial-permeability of 5–6, a quality factor of above 30 in the 200–300 MHz frequency and a resonance frequency above 1 GHz, which can be used in high frequency multilayer chip inductors.     

Effects of Ni2+ concentration on the composition,structure, magnetic properties,and DC-bias superposition characteristics of NiCuZn ferrites

Ni_xCu_0.2Zn_yFe_1.98O₄ (x = 0.16, 0.26, 0.35, 0.43, 0.50; y = 0.8?x) ferrites were prepared via solid-state reaction. The influence of Ni²⁺ concentration on ferrites composition, microstructure, magnetic properties and DC-bias superposition characteristics was studied by XRD, SEM, XPS, and VSM. Then, the effect of magnetic properties on the DC-bias superposition characteristics was analyzed. The results showed that the ferrites sintered at 900 °C for 3 h were all in pure spinel phase with an average grain size of 7.5 μm and a relative density of about 5.15 g cm^?3. With the increase in Ni²⁺ concentration, the saturation magnetization (M_s) and coercivity (H_c) of ferrites increased, but the magnetocrystalline anisotropy constant (K₁) first increased and then decreased. And the M_s, H_c, and K₁ of the specimen with x = 0.43 were 63.62 emu·g^?1, 27.36 Oe, and 1813.17 Oe·emu·g^?1, respectively. In particular, the specimen of x = 0.50 achieved the best DC superposition characteristics, where the H_70% was about 220 A m^?1. The incremental permeability of the specimens decreased rapidly at a bias magnetic field <400 A m^?1. The variation mainly originated from the domain wall displacement, and the rate of decrease was influenced by both M_s and K₁. At a bias magnetic field ≥400 A m^?1, the incremental permeability of the specimens decreased slowly, mainly because the number of domain walls decreased until disappearing, and the specimens tended to become a single domain structure. And the rate of decrease of incremental permeability was mainly affected by K₁.     

Effect of calcination temperature on optical,magnetic and dielectric properties of Sol-Gel synthesized Ni0.2Mg0.8-xZnxFe2O4 (x = 0.0–0.8)

The Ni_0.2Mg_0.8-xZn_xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6 & 0.8) nanomaterials were prepared via sol-gel technique. These samples were calcined at three different temperatures (T) such as 400, 450 and 500 °C/5 h. Furthermore, the X-ray diffraction (XRD) patterns of all the calcined samples revealed the single phase cubic spinel structure. The lattice constants (a = b = c) were noticed to be increasing with increase of ‘x’. The grain shape, size and distribution of x = 0.0–0.8 contents were analyzed using field emission electron microscope (FESEM). The x = 0.2 content provided higher optical band gap energy (E_g) value than the remaining contents. Furthermore, the magnetization versus magnetic field (M − H) curves indicated the superparamagnetic nature of x = 0.0–0.8 contents. The high saturation magnetization (M_s) was noticed for x = 0.4 and 0.6 contents. In addition, the distribution of cations like Ni⁺², Mg⁺², Zn⁺², Fe⁺³ and Fe⁺² was performed between the tetrahedral (A) and octahedral (B) sites. The frequency dependence of dielectric constant (ε′), dielectric loss (ε") and ac-electrical conductivity (σ_ac) was investigated as a function of composition. Moreover, the temperature variation of ε′ showed the decreasing trend of dielectric transition temperature (T_e) with increase of ‘x’. The high ε′ of 163.1 (at 1 MHz) was noticed at x = 0.2 content calcined at 500 °C. Using the power law fit applied to the log σ_ac-log ω plots, the dc-electrical conductivity (σ_dc) and exponent (n) parameters were calculated.     

Investigating the co-substitution impact of yttrium–nickel cations on lattice,morphological and magnetic parameters of SrM based ceramics

This study details the impact of the co-substitution of Y³⁺-Ni³⁺ ions for the Fe³⁺ ions on the structural, morphological and, magnetic parameters of SrM based SrY_xFe_12-2xNi_xO₁₉ (0.00 ≤ x ≥ 0.25) (SrYFeNiO) ceramic magnets synthesized by the ceramic route. Rietveld refinement of XRD confirmed the hexagonal (P63/mmc (194), z = 2) SrFe₁₂O₁₉ phase for all and an additional rhombohedral (R-3c (167), z = 6) hematite Fe₂O₃ phase for x = 0.2, x = 0.25 doping levels. The experimental and theoretical measurements abstracted the stretch of lattice parameters, i.e., the crystallographic axis and the lattice cell volume, and the dislocation of the crystallographic plane (1 1 4) for the hexagonal system, certified the heavy Y³⁺-Ni³⁺ ions substitution. To examine the morphological parameters, FESEM presented the regular hexagonal platelets of sizes ~ 1–2 μm, and EDX revealed the presence of constituent elements with their atomic and weight percentages in SrFeYNiO products. The extraction of vibrational frequencies of Fe–O bonds at tetrahedral and octahedral sites of iron through FT-IR spectroscopy authenticates the formation of the SrM phase. XPS correlated the doped elements, i.e., nickel in Ni⁺² and Ni⁺³ and yttrium in Y⁺³, whereas parent element, i.e., iron in Fe⁺³ and Fe⁺² chemical states, enlightened their impact on the magnetic parameters. Hysteresis loop analysis deduced a linear decline in magnetic parameters such as saturation magnetization (M_s) and remnant magnetization (M_r) due to non-magnetic Y³⁺ and less magnetic Ni³⁺ ions installment in 4f1 and 2b polyhedral sites of Fe³⁺ ions. However, high coercivity (H_c) up to 2.92 kOe ∈ x = 0.15 and extended magnetocrystalline anisotropy (MCA) up to 5.790× 10⁶ Erg/g ∈ x = 0.15 of our obtained ceramic magnets affirmed their application in permanent magnetic industry. M(T) curves also demonstrated the decrease in M_s and displayed an SPM at T_B, which is shifting towards lower temperatures with increasing Y³⁺-Ni³⁺ contents approved the expansion of lattice parameters.     

Structural,optical, electrical,dielectric, molecular vibrational and magnetic properties of La3+ doped Mg–Cd–Cu ferrites prepared by Co-precipitation technique

Ferrites are among the most frequently investigated materials mainly due to interesting and practically different properties. Therefore, easily and cost-effective lanthanum doped Mg_0.5Cd_0.25Cu_0.25Fe_2-xLa_xO₄ (x = 0.0, 0.0125, 0.025, 0.0375 and 0.05) ferrites were synthesized by a co-precipitation route, a comprehensive characterisation of their structural, optical, electric, dielectric, molecular vibrational, and magnetic properties were carried out. X-ray diffraction analysis confirmed the formation of a cubic spinel structure. Variations in frequency bands were also observed with amplification in optical band gap energy (2.95 – 3.38 eV) due to La³⁺ ions insertion. The electric resistivity had opposite trends at low and high temperatures with increasing La³⁺ content. The Curie temperature, activation energy, and drift mobility were also determined to have values consistent with the semiconducting behavior of the soft ferrites. The saturation magnetization (M_S) has a maximum value 49.385 emu/g with remanent magnetization (M_r) was 34.928 emu/g and coercivity 661.4 Oe for La³⁺ concentration x = 0.05. The minimum dielectric loss was observed for La³⁺ concentration x = 0.025. Moreover, the resistivity (ρ) has a maximum value of 7.95 × 10⁴ Ω cm for La³⁺ concentration x = 0.025. The calculated frequency range of La³⁺ doped Mg–Cd–Cu ferrites was detected in the microwave range (3.36 – 10.80 GHz), suggesting the potential application of the materials in longitudinal recording media and microwave absorbance.     

Ni-Cu-Zn ferrites with high Curie temperature for multilayer inductors with increased operating temperatures

We studied the sintering behavior and magnetic properties of Ni_0.60-yCu_yZn_0.42Fe_1.98O_3.99 ferrites. The shrinkage is shifted toward lower temperature with increasing Cu content y. The addition of Bi₂O₃ sintering aid induces enhanced shrinkage at T < 900°C and dense ceramics are obtained after sintering at 900°C. Such ferrites exhibit a permeability of µ = 135-250 depending on the composition, sintering temperature and concentration of sintering additive. Ferrites with y = 0.20 show a high Curie temperature of T_c = 307°C. Multilayer inductors were fabricated and cofired at 900°C using ferrite tapes without and with 0.75 wt% Bi₂O₃. The compatibility of ferrite tapes with different metal pastes (Ag, AgPd, and Au) was evaluated. Ferrite tapes were also integrated between layers of low-k dielectric CT708 tapes and successfully cofired at 900°C. Preliminary tests indicate that the multilayer inductors can be operated up to temperatures of 250°C. This demonstrates that high-T_c Ni-Cu-Zn ferrites are promising magnetic materials for inductive components for high operating temperatures.     

Ammonia gas sensing and magnetic permeability of enhanced surface area and high porosity lanthanum substituted Co–Zn nano ferrites

This work reports magnetic permeability and ammonia gas sensing characteristics of La³⁺ substituted Co–Zn nano ferrites possessing chemical formula Co_0.7Zn_0.3La_xFe_2-2xO₄ (x = 0–0.1) synthesized by a sol-gel route. Refinement of X-ray diffraction (XRD) patterns of the ferrite powders by the Rietveld technique has revealed the creation of single-phase spinel structure. The tenancy of constituent cations at tetrahedral/octahedral sites was obtained from the refinement of XRD. The crystallite sizes calculated from the W–H method vary from 20 to 24 nm. The scanning electron microscope (SEM) profiles of the ferrite samples were analyzed for the morphological details. The energy dispersive X-ray analysis (EDAX) patterns of the samples were obtained to test the elemental purity of the ferrites within their stoichiometry. The transmission electron microscope (TEM) image of the ferrite (x = 0.1) exhibits the spherical and oval shaped particles with a mean size of 20 nm. Fourier transform infra-red (FTIR) spectra were analyzed to confirm the superseding of La³⁺ cations at octahedral sites. The Brunauer-Emmett-Teller (BET) analysis of nitrogen adsorption-desorption isotherms of the ferrites was performed to investigate the porous structure and to determine the surface area of the nanocrystalline ferrites. The oxidation states of the constituent ions were confirmed by means of X-ray photoelectron spectroscopy (XPS). The complex permeability as a function of frequency was studied to explore the effects of structural parameters on the magnetic behaviour of the ferrites. Analysis of gas sensing properties of the ferrites have proved that the Co–Zn–La ferrite with controlled La composition can be utilized as an effective ammonia gas sensing material in commercial gas sensors.     

Microstructure and magnetic properties of nickel-zinc ferrite ceramics fabricated by spark plasma sintering

Dense nickel-zinc (NiZn) ferrite ceramics were successfully fabricated within tens of seconds via spark plasma sintering. The phase composition and microstructure of the sintered samples were characterized by X-ray diffraction and scanning electron microscopy, respectively. The static magnetic properties at room temperature and Curie temperature of the samples were investigated by vibrating sample magnetometry. The results indicated that the main phase of the sintered samples was Ni_0.75Zn_0.25Fe₂O₄ with spinal structure, and the sintering temperature and heating rate observably affected the microstructure and density, then the magnetic properties of the sample. The Joule heat generated by NiZn ferrite during spark plasma sintering was very important for the rapid preparation of the sample with high density and small grain size. The low sintering temperature and heating rate would be helpful to obtain samples with small grain size, high density, and then good magnetic properties. The samples sintered at 900 °C with the heating rate of 5–10 °C/s were characterized of the relative density above 95%, 4πM_s value beyond 4000 Gs and coercivity below 27.7 Oe.     

Single-phase and binary phase nanogranular ferrites for magnetic hyperthermia application

The study demonstrates the performance of heating efficiency in single-phase and binary phase spinel ferrite nanosystems. Ferrimagnetic cobalt ferrite (CoFe₂O₄) (CFO) and superparamagnetic copper ferrite/copper oxide (CuFe₂O₄/CuO) (CuF) nanosystems of different particle sizes were synthesized through a microwave-assisted coprecipitation method. The heating behavior was observed in range of both field amplitudes (8-24 kA/m at 516 kHz) and frequencies (325-973 kHz at 12 kA/m). The heating efficiency was analyzed and compared by means of particle size, magnetization, effective anisotropy constant, and Néel relaxation mechanism. Indeed, the heating rate was maximized in larger ferrite particles with low effective anisotropy constant. Moreover, though the magnetization and effective anisotropy constant of single-phase CoFe₂O₄ nanoparticles were higher, the binary phase CuFe₂O₄/CuO nanosystems of similar crystallite size (28 nm) exhibited superior heating efficiency (4.21°C/s). For a field amplitude and frequency of 24 kA/m and 516 kHz, the heating rate of CuF and CFO ferrites with different crystallite sizes decreased in the order of 4.21 > 2.14 > 0.58 > 0.52°C/s for 29 nm > 25 nm > 12 nm > 15 nm, respectively. The results emphasize that binary phase ferrite nanoparticles are better thermoseeds than the single-phase ferrites for the magnetic hyperthermia application.     

Low-dielectric-constant LiAlO2 ceramics combined with LBSCA glass for LTCC applications

This study used Li₂O–B₂O₃–SiO₂–CaO–Al₂O₃ (LBSCA) glass to reduce the sintering temperature of LiAlO₂ ceramics and to realise the low dielectric constants (ɛ_r<5) of low-temperature co-fired ceramic (LTCC) materials. LBSCA glass remarkably enhanced the densification of LiAlO₂ ceramics. X-ray diffraction patterns indicated that only the γ-LiAlO₂ phase occurred within the doping range of 1 wt% to 3.5 wt%. Scanning electron microscopy images showed dense and uniform grains in samples with 3.0 wt% LBSCA glass. These samples also exhibited low dielectric constants and low dielectric loss when sintered at 900 °C and 950 °C (i.e., ɛ_r=4.48, Qf=35,540 GHz and τ_f=−53 ppm/°C at 900 °C; ɛ_r=4.50, Qf=38,979 GHz and τ_f=−55 ppm/°C at 950 °C, respectively). The material prepared was chemically compatible with silver and showed potential in applications of high-frequency LTCC microwave substrates.     

Microstructure and enhanced magnetic properties of low-temperature sintered LiZnTiMn ferrite ceramics with Bi2O3-Al2O3 additive

Bi₂O₃ and Al₂O₃ were proven to separately have an impact on grain growth of LiZn ferrite ceramics. In this study, we synthesized LiZnTiMn ferrite ceramics under low temperature (<920 °C) using rationally designed formula of Bi₂O₃-Al₂O₃ as sintering agents. Microstructures, densities, and ferromagnetic performances were systematically investigated. Results show that appropriate amount of Bi₂O₃-Al₂O₃ leads to successful sintering of LiZnTiMn ferrites even below 900 °C. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) results show that spinel structure ferrite ceramics were obtained and that the addition of Bi₂O₃-Al₂O₃ accelerated solid-state reaction. Corresponding ferromagnetic properties, including saturation induction (B_s), remanence square ratio, coercivity (H_c), ferromagnetic resonance linewidth (ΔH), and M_s, were also investigated. At 920 °C, with addition amount of x=1 wt%, we obtain excellent performance: B_s=306 mT, B_r/B_s=0.849, H_c=2.34Oe, and ΔH=275 Oe. Results indicate that Bi₂O₃-Al₂O₃ is promising sintering agent for low-temperature sintering of LiZnTiMn ferrite ceramics.     

Influence of zinc and cadmium co-doping on optical and magnetic properties of cobalt ferrites

Zinc and cadmium based cobalt ferrites Zn_xCd_0.375-xCo_0.625Fe₂O₄ (where x = 0, 0.075, 0.125, 0.25) were successfully synthesized by a facile co-precipitation technique. Structural, optical and magnetic characteristics of the doped ferrites were systematically analyzed. X-ray Diffraction (XRD) pattern confirmed the formation of cubic spinel structure in all samples. Scanning electron microscopic analysis of surface morphology revealed cubic and spherical shaped ferrite particles. Fourier transform infrared (FTIR) spectroscopy confirmed the existence of metal oxygen (M − O) bonding in the prepared samples. Moreover, the prepared samples exhibited two frequency bands corresponding to phonon vibrational stretching in both octahedral and tetrahedral lattice positions. The optical properties were investigated in detail through photoluminescence (PL) spectroscopy and Raman spectroscopy. The PL spectrum confirmed the strong emission peaks in the ultraviolet to visible region of all the samples. Further, four active Raman modes, associated with cubic spinel structure are identified in all prepared samples. Finally, the magnetic characteristics are evaluated by using vibrating sample magnetometer (VSM) revealing ferrimagnetic and soft magnetic behavior of the samples. As the Zn and Cd co-doping in Co was increased, the H_c was decreased. The magnetic studies show the maximum H_c of 576 Oe for Cd doped cobalt ferrite, and maximum saturation magnetization (M_s) for Zn–Cd doped cobalt ferrite. It is envisaged that the newly prepared Zn–Cd co-doped cobalt ferrite would be appropriate for a number of important applications, for example, magnetic recording devices, sensors, actuators, high-density data storage devices, and biomedical equipments.     

Effect of a YIG nanoparticle additive on the magnetic properties of MnZn ferrites for MHz frequency applications

In this study, MnZn ferrites with added YIG nanoparticles were developed for MHz frequency applications. The effect of the magnetic YIG additive on the power loss, initial permeability, and cutoff frequency of MnZn ferrites was investigated. A small quantity of added YIG effectively reduces the power loss and concurrently increases the initial permeability. Compared to the results for the MnZn ferrite with no added YIG, the optimal MnZn ferrite with 600 ppm added YIG exhibits a reduction in the power loss at 25°C of 56.4% and 36.6% at 1 MHz/50 mT and 3 MHz/10 mT, respectively, and a 13.9% increase in the initial permeability. This sample also exhibits a good stability of the power loss against temperature. The power loss remains below 205 kW/m³ over temperatures ranging from 25 to 140°C. The effect mechanism of YIG addition on the magnetic properties of MnZn ferrites was studied. An analysis based on the equivalent circuit model showed that the reduction in the eddy current loss and power loss mainly results from the increase in the grain boundary resistance caused by the addition of highly resistive YIG.     

The influence of lanthanum concentration on microstructural and electrical properties of Mg-Cd-Bi ferrite nanoparticles

Lanthanum (La³⁺) substituted Mg-Cd-Bi ferrite nanoparticles were synthesized by sol-gel auto combustion route consuming high quality nitrates. The impact of lanthanum concentration on microstructural and electrical properties in the ferrite series Mg_0.5Cd_0.5Fe_1.95Bi_0.5-xLa_xO₄ (x = 0.0, 0.01, 0.02, 0.03, 0.04, 0.05) was investigated. The samples were characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), scanning electron microscope (SEM), and Current-voltage (I-V) analyzerfor compositional, structural, morphological and electrical analysis. Upon varying the lanthanum content, it is observed that all the samples retained perovskite BiFeO₃ phase with distorted rhombohederal structure. Furthermore, it is revealed that the sintering process can significantly control the structural defects and crystal imperfections which affect the electric and magnetic nature of ferrites. The conduction process in La³⁺-dopedferrite series is originated by the hopping of electrons between ions of same elementswhich reduced the electrical resistivity and depicts the semiconductor nature of synthesized samples.Thus, it is believed that the optimal doping of lanthanum content in La³⁺-substituted Mg-Cd-Bi ferrites followed by post-annealing can remarkably tune the electrical properties of synthesized ferrite nano particles.     

Microstructure,magnetism, and high-frequency performance of polycrystalline Ni0.5Zn0.5Sm0.025HoxFe1.975−xO4 ferrites

Novel polycrystalline Ni_0.5Zn_0.5Sm_0.025Ho_xFe_1.975−xO₄ (x = 0-0.06) ferrites were fabricated by a traditional solid-state reaction sintering method. The codoping effects of Sm and Ho on the microstructure, magnetism, and high-frequency performance of Ni–Zn ferrites were investigated. The substitution of Sm³⁺ and Ho³⁺ ions led to an apparent increase in the lattice constants. However, further increasing the addition of both dopants introduced SmFeO₃ or HoFeO₃ foreign phases at the boundaries of the polycrystalline grains. As the content of Ho³⁺ ions increased, the relative density and average grain size of the specimens decreased accordingly. Moreover, the substitution of Sm³⁺ clearly decreased the saturation magnetization and complex permeability, which further decreased with the doping of Ho³⁺. The evolution of the Curie temperature showed an opposite trend, reaching the highest temperature of 278°C when x = 0.03. Similarly, the coercivity and resonance frequencies also displayed opposite trends compared to those of the saturation magnetization and complex permeability. The codoping of Sm³⁺ and Ho³⁺ more effectively lowered the magnetic and dielectric loss tangent of the specimens compared with the undoped or single dopant modified ferrites.     

A comparative study of the magnetic and microwave properties of Al3+ and In3+ substituted Mg–Mn ferrites

The effect of substitution of diamagnetic Al³⁺ and In³⁺ ions for partial Fe³⁺ ions in a spinel lattice on the magnetic and microwave properties of magnesium–manganese (Mg–Mn) ferrites has been studied. Three kinds of Mg–Mn based ferrites with compositions of Mg_0.9Mn_0.1Fe₂O₄, Mg_0.9Mn_0.1Al_0.1Fe_1.9O₄, and Mg_0.9Mn_0.1In_0.1Fe_1.9O₄ were prepared by the solid-state reaction route. Each mixture of high-purity starting materials (oxide powders) in stoichiometric amounts was calcined at 1100 °C for 4 h, and the debinded green compacts were sintered at 1350 °C for 4 h. XRD examination confirmed that the sintered ferrite samples had a single-phase cubic spinel structure. The incorporation of Al³⁺ or In³⁺ ions in place of Fe³⁺ ions in Mg–Mn ferrites increased the average particle size, decreased the Curie temperature, and resulted in a broader resonance linewidth as compared to un-substituted Mg–Mn ferrites in the X-band. In this study, the In³⁺ substituted Mg–Mn ferrites exhibited the highest saturation magnetization of 35.7 emu/g, the lowest coercivity of 4.1 Oe, and the highest Q×f value of 1050 GHz at a frequency of 6.5 GHz.     

Highly c-axis oriented W-type hexaferrites SrNi2ScxFe16-xO27 (x = 0.70, 0.75, 0.80 and 0.85) for the design of self-biased circulator at Ku band

Highly oriented W-type hexaferrites SrNi₂Sc_xFe_16-xO₂₇ (SrW, x = 0.70, 0.75, 0.80 and 0.85) are fabricated via ceramic process and magnetic orientation to meet design requirements of self-biased circulators. The orientation degree reaches 0.81 when Sc³⁺ substitution content x is 0.75. The XRD refinement results in consideration of orientation illustrate the strong c-axis anisotropy texture of SrW. SEM images show significant uniformity in grain growth with c-axis stays vertical to sample plane. Consequently, the corresponding remanence ratio M_r/M_s reaches as high as 0.92, which is indispensable to reduce low field loss (LFL) as much as possible in the design of self-biased circulators. According to simulation results, the self-biased microstrip circulator based on this SrW material (x = 0.75) realizes ideal functions in circular transmission operating at Ku band.     

Structural and magnetic properties of ZnMg-ferrite nanoparticles prepared using the co-precipitation method

We synthesized soft magnetic spinel ferrite ZnMg-ferrite (Zn_1?xMg_xFe₂O₄, where x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles using the co-precipitation method. Structural and magnetic properties have been studied in detail. XRD revealed that the structure of these nanoparticles is spinel with crystallite size lies in the range 21–31 nm. Lattice parameter decreases with increasing Mg concentration due to the smaller ionic radius of the Mg²⁺ ion. FTIR spectroscopy also confirmed the formation of spinel ferrite by showing the characteristic absorption bands at 420 cm^?1 and 545 cm^?1. Vibrational band of metal ion at tetrahedral site (M_tet.) with oxygen ions (O–M_tet.–O) is shifted toward higher wave numbers with the increase of Mg concentration. The magnetization showed an increasing trend with increasing Mg concentration due to the rearrangement of cations at tetrahedral and octahedral sites, while the corecivity remained constant due to the soft nature of the ferrite composition. Both structural and magnetic properties of ZnMg-ferrite nanoparticles strongly depend upon Mg²⁺ cation doping percentage.