W-type Hexaferrite Research Articles

Dopant site occupancies and iron valence states in SrZnxFe18−xO27 W-type hexaferrites using site-selective X-ray/electron spectroscopy

Zn-doped W-type Sr hexaferrite (SrZnxFe18−xO27; SrZnx-WHF) is an anticipated rare-earth-free hard magnetic material with strong magnetocrystalline anisotropy and saturation magnetization. To examine the origin of its high magnetic performance, the site distribution of Zn over seven crystallographically inequivalent Fe sites and the site-dependent valence states of Fe were investigated using site-selective elemental/chemical analysis techniques. The dominant occupation of Zn2+ at the 4etet(S) and 4ftet(S) tetrahedral sites was determined quantitatively using high-angular-resolution electron-channeling X-ray spectroscopy and statistical data analysis. The combined application of high-angular-resolution electron channeling electron spectroscopy and atomic-column resolution scanning transmission electron microscopy–electron energy-loss spectroscopy helped unambiguously clarify that most of the Fe2+ ions existed at the 6goct(S-S) octahedral site. Density functional theory calculations have shown that Zn doping leads to a redistribution of the charges toward Fe ions at this site. This redistribution preserves the local charge balance and amplifies the total number of parallel spins. Hence, the enhanced magnetocrystalline anisotropy and saturation magnetization in SrZnx-WHF can be inferred to originate from the charge redistribution at the 6goct(S-S) site, which is influenced by the presence of nonmagnetic Zn.

Physicochemical, morphological, and charge carrier mobility range dielectric evaluations of Yb-doped BaCo2 W-type hexagonal ferrites for high-frequency applications

Microwave absorption materials have attracted attention due to their extensive applications in different fields. Herein, ytterbium-doped BaCo2 W-type hexaferrite nanocrystallites with a nominal composition of BaCo2YbxFe16−xO27 (x = 0.00, 0.03, 0.06, 0.09, and 0.12) were synthesized via the sol–gel method, and their physicochemical and dielectric characteristics were estimated. XRD plots revealed the pure phase structure of each prepared hexaferrite sample. The lattice constant and unit cell volume were affected by changes in the Yb concentration. The crystallite size was measured by the Debye–Scherrer formula, revealing intense crystals typically in the 18–33 nm range. FTIR spectroscopy showed multiple absorption bands from 430 to 3000 cm−1, and Raman spectroscopy revealed multiple peaks between 200 and 1000 cm−1, displaying the allocated polyhedra and symmetry. XPS spectroscopy confirmed the existence of all metal ions in the required valence state. The dielectric measurements were evaluated at frequencies from 1 to 6 GHz for all the synthesized compositions, and the material behavior was explained using the Maxwell–Wagner and Koop theories. The conduction mechanism in the hexagonal ferrites was assessed using Cole–Cole analysis. Reflection loss measurements were also conducted: the samples at x = 0.03 and x = 0.12 yielded minimal reflection losses of −60.06 and −51.69 dB at 5.5 GHz, respectively. The results demonstrate the suitability of the samples for use in microwave and high-frequency absorption applications.

Impact of Gd-substitution on structural, dielectric, spectroscopic, Raman, and photo luminance properties of Ba0.4Sr0.6Co2Fe16O27 ceramics

This paper represents a detailed study of Gd3+ substitutions on Structural, Dielectric, Spectroscopic, Raman, and Photo luminance Properties of Ba0.4Sr0.6Co2Fe16O27 magnetic oxides were prepared using the sol-gel auto combustion method. All of these specimens were sintered at 1100 °C for 5 h. X-ray diffraction analysis (XRD) confirmed the single-phase detection and structural analysis. The lattice parameters a and c show the insignificant behavior 5.893–5.933 Å, and 32.049–32.476 Å with the concentration of gadolinium ions. The crystallite size ranged from 25 to 30 nm, demonstrating a growing tendency as Gd-substitution was enhanced. The discrepancy in the ionic radii of iron (Fe3+) and substituent elements (Gd3+) is the cause of the variation in cell volume and lattice constants. FTIR spectroscopy confirmed the presence of absorption bands (590 and 3000 cm−1) for prepared BaSr-based W-type hexa-ferrites. The vibrational bands of metal oxide ions are responsible for the 590 and 685 cm−1 peaks. The Raman spectrum showed six discrete, brittle peaks: 320, 440, 620, 690, 1300, and 1600 of synthesized nanomaterials—the dielectric constant and dielectric loss increase by substituting the Gd3+ ion. The dielectric parameters and dielectric loss at higher frequencies suggest that the prepared material may be excellent for switching, sensing, and high-frequency applications.

Structural, optical, dielectric and magnetic properties of Cd substituted copper strontium W-type hexaferrite

Hexaferrites, with their exceptional crystalline anisotropy, substantial coercivity, tuneable cations, and high magnetic hardness, are crucial as permanent magnets in applications such as information storage, sensors, high-frequency and microwave-absorbing devices. In this study, the focus was on synthesizing copper and cadmium-substituted strontium W-type hexagonal ferrites (SrCu2-xCdxFe16O27) with varying x values of 0.00, 0.01, 0.02, 0.03, and 0.04. To comprehensively investigate their structural, morphological and optical characteristics, several analytical techniques were employed, including XRD, SEM, FT-IR spectroscopy and UV–Vis spectroscopy along with dielectric and magnetic techniques. The XRD analysis showed a minimum crystallite size of 13 nm for x = 0.0 and a maximum of 21 nm for x = 0.04. The morphology was examined through SEM, affirming the characteristic structure of W-type hexaferrites. FT-IR spectra exhibited two prominent peaks at 491 cm−1 and 890 cm−1, further validating the creation of W-type hexaferrites. Notably, the UV–Vis spectroscopy demonstrated a reduction in the optical band gap from 2.41 to 2.11 eV with increasing concentrations. In terms of dielectric properties, a peak dielectric constant of 71 was observed at frequencies above 2.5 GHz. Furthermore, the AC conductivity displayed a linear trend at lower frequencies, reaching a maximum value of 0.35 [ohm cm]−1 at higher frequencies. The magnetic measurements indicated that the substitution of x = 0.04 exhibited the highest saturation magnetization, Ms value of 1.7 emu/g, but the lowest coercivity, Hc value of 75 Oe was observed.

Dielectric, physicochemical, and reflection loss features of Gd-substituted W-type hexaferrites for microwave absorption application

Dielectric, physicochemical, and reflection loss features of Gd-substituted W-type hexaferrites for microwave absorption application

Correction: Multi-characterization for Electromagnetic Interference in Electronic Circuits for CaPb-based W-type Hexaferrites

Correction: Multi-characterization for Electromagnetic Interference in Electronic Circuits for CaPb-based W-type Hexaferrites

Structural, Raman, Photo luminance, morphological, and magnetic properties of Sr-Ba-Cu–Zn W-type hexaferrites

Structural, Raman, Photo luminance, morphological, and magnetic properties of Sr-Ba-Cu–Zn W-type hexaferrites

The Effect of Carbon Nanotubes in Improving the Electromagnetic Behavior of W-type Hexaferrite Nanoparticles Doped With Mn and Ca Cations

The Effect of Carbon Nanotubes in Improving the Electromagnetic Behavior of W-type Hexaferrite Nanoparticles Doped With Mn and Ca Cations

Absorption Band Tunable La-Sr Co-Doped BaCo2-W Type Hexaferrites.

La-Sr co-doped Ba1-x(La0.5Sr0.5)xCo2Fe16O27 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, respectively) hexaferrites were prepared by the solid-state method. W-type hexaferrite single phase structure with space group P63/mmc was obtained when the doping amount was x < 0.4 and an M-type hexaferrite and a spinel phase with smaller grains gradually replaced the W phase as the primary phases when x ≥ 0.6. The maximum Ms is 76.2 emu/g and the minimum Hc is 60 Oe at x = 0.4, as obtained by VSM analysis. The magnetoelectric properties of the samples were tested at 1-18 GHz with a vector network analyzer and the reflection loss was calculated based on transmission line theory. It was found that the introduction of an appropriate amount of La-Sr provides a large number of porosity defects while increasing the grain size, which can effectively improve the reflection of electromagnetic waves inside the material and dissipate more energy. At the same time, co-doping also makes the resonance frequency of the samples shift to lower frequency, resulting in tunable absorption properties in the C, X and Ku bands. When x = 0.2, the minimum reflection loss is -40.61 dB at 1.5 mm thickness, with the effective absorption bandwidth of 5.76 GHz in the X band; when x = 0.4, the minimum reflection loss is -37.45 dB at 2.5 mm, with the bandwidth of 4.97 GHz in the C band; when x = 0.6, the material has good absorption in both the X and Ku bands with the thickness less than 2 mm. The simple preparation method and good performance make La-Sr co-doped Co2W ferrite a promising microwave absorbing material.

Multi-characterization for Electromagnetic Interference in Electronic Circuits for CaPb-based W-type Hexaferrites

Multi-characterization for Electromagnetic Interference in Electronic Circuits for CaPb-based W-type Hexaferrites

Tunable and broad-band electromagnetic wave absorption using W-type Hexaferrites in 1–40 GHz range

W-type Sr-hexaferrites, Sr0.75Ca0.25Zn2-xCoxFe16O27 (0.0 ≤ x ≤ 2.0), were synthesized, and their magnetic and electromagnetic (EM) wave absorption properties were investigated. As x increased from 0.0 to 2.0, the saturation magnetization value increased and reached a maximum at x = 1.25, followed by a decrease, while the magnetic anisotropic field (Hani) decreased and showed a minimum at x = 1.0, then increased again. The variation in Hani could be controlled by adjusting the value of x, which also changed the ferromagnetic resonance (FMR) frequency and enabled control over the frequency band of EM wave absorption. It is demonstrated that the EM wave absorption is primarily controlled by imaginary part of permeability (μ") induced by FMR. Composite of the W-type hexaferrite-epoxy (10 wt%) with x = 0.75–2.0 showed a broad-band EM wave absorption in the 1–18 GHz range, while the composites with x = 0–0.4 showed it in the 26.5–40 GHz. The x = 1.25 sample satisfied RL < − 10 dB in the 7–17 GHz range with a thickness of 2.1 mm, while x = 0.3 sample satisfied RL < − 10 dB in the 27–39 GHz with a thickness of 0.8 mm. Sr0.75Ca0.25Zn2-xCoxW is a very promising material for tunable wideband EM wave absorbers in 1–40 GHz range.

Controlling the magnetic structure in W-type hexaferrites.

W-type hexaferrites with varied Co/Zn ratios were synthesized and the magnetic order was investigated using neutron powder diffraction. In SrCo2Fe16O27 and SrCoZnFe16O27 a planar (Cm'cm') magnetic ordering was found, rather than the uniaxial ordering (P63/mm'c') found in SrZn2Fe16O27 which is common in most W-type hexaferrites. In all three studied samples, non-collinear terms were present in the magnetic ordering. One of the non-collinear terms is common to the planar ordering in SrCoZnFe16O27 and uniaxial ordering in SrZn2Fe16O27, which could be a sign of an imminent transition in the magnetic structure. The thermomagnetic measurements revealed magnetic transitions at 520 and 360 K for SrCo2Fe16O27 and SrCoZnFe16O27, and Curie temperatures of 780 and 680 K, respectively, while SrZn2Fe16O27 showed no transition but a Curie temperature at 590 K. This leads to the conclusion that the magnetic transition can be adjusted by fine-tuning the Co/Zn stoichiometry in the sample.

Quantifying Co–Zn contents for compositional tailoring of strontium W-type hexaferrites for useful applications

Structural, optical, dielectric, and magnetic characteristics of Sr–Ni–W hexaferrites were probed to justify their potential use in various applications. Sr1-xCoxZnyNi2-yFe16O27 (WHFs) ferrites were synthesized by the self-combustible sol-gel method. XRD analysis confirmed a single-phase material with different Co–Zn contents. Fourier transform infrared spectroscopic (400-4000 cm−1) analysis was performed. Variations in Raman intensities indicated the induction of local strain due to a mismatch of ionic radii. The energy band gap (1.879 eV) was calculated from photoluminescence spectra, indicating the semiconducting nature of materials. SEM images showed the presence of grains with hexagonal platelet morphology oriented irregularly, which is highly beneficial for microwave absorption. The high coercivity values indicated that the materials are magnetically hard. Magnetic analysis revealed the potential use of materials in high-storage applications. Dielectric properties were determined using a vector network analyzer within a frequency span (0–6 GHz), indicating materials' usefulness in constructing resonant circuits and MLCIs.

Texture formation in W-type hexaferrite by cold compaction of non-magnetic interacting anisotropic shaped precursor crystallites.

Crystallites of the W-type hexaferrites, Sr(Ni1-xZnx)2Fe16O27 (x = 0, 0.5, 1) have been aligned without applying magnetic field nor hot compaction, but through a simple synthesis process taking advantage of easy alignment of non-magnetic interacting, anisotropic-shaped precursor crystallites of goethite. The goethite precursor was prepared through a simple hydrothermal synthesis route, forming lathlike crystallites with apparent dimensions of 23.3 × 40.1 × 11.0 nm3 as extracted from powder X-ray diffraction along the a-, b- and c-axis, respectively. The calcined pellets consisted of almost phase pure W-type hexaferrites with relative small impurities of spinel ferrite (≤9.02(3) wt%). The high synthesis temperature resulted in large crystallites, which in turn caused low coercivities (Hc ≤ 5.4(1) kA m-1) and a squareness ration (Mr/Ms, remanence (Mr) over saturation magnetisation (Ms)) close to zero for all samples. The vanishing coercivity makes Mr/Ms an unsatisfying measure of preferred orientation. Quantitative texture analysis of the samples was carried out based on 2D transmission synchrotron diffraction data collected at different orientations of the samples. The texture investigations revealed alignment of the crystallites with the c-axis normal to the pressing surface of the pellets. The SrNi2Fe16O27 sample showed the highest texture index of 7.5 m.r.d.2.

Two-Step Calcination-Method-Derived Al-Substituted W-Type SrYb Hexaferrites: Their Microstructural, Spectral, and Magnetic Properties

W-type hexaferrites were discovered in the 1950s and are of interest for their potential applications. In this context, many researchers have conducted studies on the partial substitution of Fe sites in order to modify their electric and magnetic properties. In this study, W-type SrYb hexaferrites using Al3+ as substitutes for Fe3+ sites with the nominal composition Sr0.85Yb0.15Zn1.5Co0.5AlxFe16−xO27 (0.00 ≤ x ≤ 1.25) were successfully synthesized via the two-step calcination method. The microstructures, spectral bands of characteristic functional groups, morphologies, and magnetic parameters of the prepared samples were characterized using XRD, FTIR, SEM, EDX, and VSM. The XRD results showed that, compared with the standard patterns for the W-type hexaferrite, the W-type SrYb hexaferrites with the Al content (x) of 0.00 ≤ x ≤ 1.25 were a single-W-type hexaferrite phase. SEM images showed the flakes and hexagonal grains of W-type hexaferrites with various Al content (x). The saturation magnetization (Ms) and magneton number (nB) decreased with Al content (x) from 0.00 to 1.25. The remanent magnetization (Mr) and coercivity (Hc) decreased with Al content (x) from 0.00 to 0.25. Additionally, when the Al content (x) ≥ 0.25, Mr and Hc increased with the increase in the Al content (x). The magnetic anisotropy field (Ha) and first anisotropy constant (K1) increased with the Al content (x) increasing from 0.00 to 1.25. Al-substituted W-type SrYb hexaferrites with soft magnetic behavior, high Ms, and lower Hc may be used as microwave-absorbing materials.

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 SrNi2ScxFe16-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 Mr/Ms 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.

Optimization of structural, electrical, and magnetic properties of ytterbium substituted W-type hexaferrite for multi-layer chip inductors

The rare earth (Yb3+) substituted W-type hexagonal ferrites with composition CaPb2-xYbxFe16O27 (x = 0.0, 0.5, 1.0, 1.5, 2.0) were synthesized by a facile and cost-effective sol-gel auto combustion method with post heat treatment. The synthesized hexagonal ferrites were characterized by a variety of analytical techniques, and an impedance analyzer was used to investigate the effects of Ytterbium on structural, magnetic, spectral and dielectric properties. The relationship between their impedance, structure and dielectric properties was investigated. The X-ray diffraction patterns verify the presence of single-phase W-type hexagonal ferrites. Physical properties such as Dbulk (bulk density), Dxrd (X-ray density), and P (porosity) of the CaPb2-xYbxFe16O27 W-type hexagonal ferrites were calculated. The bulk density of all the samples was decreased, and X-ray intensity was increased with the Ytterbium replacement in the W-type hexaferrite. By adding Yb3+ ions, the lattice parameters, cell volume and X-ray density were reduced due to the substitution of ytterbium with smaller ionic radii compared to the lead ion with large ionic radii. The AC-conductivity was increased from (1.523 × 10−5 to 6.699 × 10−5) Ωcm−1. The dielectric constant and tangent loss was found to decrease substantially. The magnetic properties were found to enhance by the substitution of Yb3+. The low coercivity value of Yb3+ substituted W-type hexagonal ferrites are suitable for magnetic recording media operated at a high-frequency regime. The enhancement of electrical, dielectric and magnetic characteristics suggests these materials as promising for multi-layer chip inductors (MLCIs) circuit applications.

Investigation into the Structural, Spectral, Magnetic, and Electrical Properties of Cobalt-Substituted Strontium W-Type Hexaferrites

The solid-state reaction method is used to synthesize W-type Sr hexagonal ferrites Sr0.8Pr0.2(Zn1.0−xCox)2Fe16O27 (x = 0.00, 0.15, 0.30, 0.45, 0.60, 0.75). The results of XRD for the W-type hexagonal ferrites, when Co content (x) is 0.00 ≤ x ≤ 0.75, exhibit that they are in the single W-type hexaferrite phase. As shown by morphological analysis, the particles are hexagonal-shaped platelets. The saturation magnetization (Ms) and magneton number (nB) increases with Co content (x) from 0.00 to 0.60. Ms and nB begins to decrease at Co content (x) ≥ 0.60. With increasing Co content (x) from 0.00 to 0.75, the magnetic anisotropy field (Ha), first anisotropy constant (K1), and coercivity (Hc) decrease gradually. The values of DC electrical resistivity for W-type hexagonal ferrites Sr0.8Pr0.2(Zn1.0−xCox)2Fe16O27 (0.00 ≤ x ≤ 0.75) are in the range of 20.854 × 107 Ω-cm and 22.755 × 107 Ω-cm.

Improved coercivity of W- and M-type composite hexaferrites using two different synthesis routes

Two series of W- and M-type composite hexaferrites were synthetized using the conventional ceramic method in two different synthesis routes. In the first synthesis route, W- and M-type composite hexaferrites were formed by reaction in the pre-sintering stage. In the second synthesis route, W- and M-type composite hexaferrites were obtained by physically mixing W- and M-type hexaferrites in the second ball milling stage. The influence of M-type phase on the structure and magnetic properties of W-type hexaferrites synthesized in both synthesis routes are investigated in detail. For both synthesis routes, X-ray diffraction (XRD) patterns of all samples indicated crystallization of W- and M-type hexaferrites phase and scanning electron microscopy (SEM) measurements revealed hexagonal platelet-like grains. In the pre-sintering stage, the saturation magnetization (4πMs) of all samples ranged between 3.30 kG and 4.25 kG. The remanence ratio (Mr/Ms) changed from 0.77 to 0.88 with the increase of pre-sintering temperature. The coercivity (Hc) of all samples ranged between 456 Oe and 1846 Oe. The ferromagnetic resonance (FMR) linewidth (ΔH) ranged between 466 Oe and 748 Oe. In the second ball milling stage, 4πMs and Mr/Ms maintained a relatively stable value of ~4.5 kG and ~0.89, respectively. Hc increased from 519 Oe to 620 Oe with the increase of M-type hexaferrites. ΔH ranged between 317 Oe and 573 Oe. We note that in both synthesis routes only the composite hexaferrites synthesized in the pre-sintering stage have a significantly improved coercivity from 456 Oe to 1846 Oe. This enhancement in coercivity is attributed mainly to the effect of exchange coupling among ferrite grains. In addition, the ΔH decreases with the addition of M-type hexaferrites.

Phase stability of SrZnxFe(2−x)Fe16O27 (0.0 ≤ x ≤ 1.0) in low oxygen pressures

The phase stability of Zn-substituted strontium W-type hexaferrites (SrZnxFe(2-x)Fe16O27; SrZnxFe(2-x)W) in the low oxygen pressure (PO2) of 10−3 atm, and strontium W-type hexaferrite (SrFe18O27; SrW) in the PO2 region of 10−3–10−2 atm were systemically investigated. For this study, polycrystalline samples were sintered at high temperatures in low PO2 and then furnace-cooled. Analyses of the phases and microstructures of sintered samples revealed that the SrZnxFe(2-x)W phases are thermodynamically stable at the temperature regions of 1245–1320 °C, 1210–1285 °C, and 1190–1255 °C, for x = 0.0, 0.5, and 1.0, respectively in the PO2 of 10−3 atm. In addition, the SrW phase was found to be stable at the temperature region between 1245 and 1320 °C, and 1275 and 1380 °C in the PO2 of 10−3 and 10−2 atm, respectively, which enabled the construction of stability phase diagram of SrW on the PO2 versus 10 000/T (K) plot in the PO2 region of 10−3 to 0.21 atm.