Type Hexagonal Ferrite Research Articles

Sol-gel synthesis of Cobalt-Bismuth substituted strontium hexaferrites and insight into structural refinement, Microstructural, dielectric and spectroscopic properties

Bi and Co-substituted strontium (SrFe12O19) hexaferrites were synthesized using the auto-combustion sol–gel method. The structural, Rietveld refinement, microstructural, spectroscopic, and dielectric characterizations were analyzed with X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and Dielectric analysis, respectively. The XRD investigation of Sr1-xBixFe12-yCoyO19 with (x = 0–0.5, y = 0–1.0) confirmed the single phase of M−type hexagonal ferrites. The change in the value of lattice constant ‘a’ in between 5.87 and 5.95 and ‘c’ 22.07 to 23.81 to be noted. The crystallite size of prepared specimens was determined in (20–29) nm range. The specific stretching vibrations in the FTIR results approves (Fe/Co-O and Bi-O) at three different positions 437.59, 549.94, and 587.53 cm−1. The existence of these band from 437 to 588 cm−1 confirmed the hexagonal structure of these ferrites. The force constants at octahedral sites increased from 1.75 to 2.02 (Dyne cm−1) x 105 and shows insignificant behavior at tetrahedral sites in between (3.33–3.54) Dyne cm−1 x 105 with Bi-Co substitution. The first band 582 cm−1 (ʋ1), is due to the maximum restoring force and vibrations at the tetrahedral site. The second band at a lower wavenumber of ∼ 402 cm−1 (ʋ 2) is due to the vibrations at the octahedral site. The microstructure of all synthesized samples of M−type hexagonal ferrites confirmed using the SEM analysis. The dielectric measurements in 0 to 3 GHZ frequency was done and effect of Bi-Co has been observed. The dielectric constant of all specimens shows the increasing trend from 1.5 GHz to 2.5 GHz with the frequency of the applied AC field. A slight increase was observed in the AC conductivity of these ferrites with the increasing concentration of Bi and Co ions.

Dielectric, reflection loss and physicochemical studies of Cr doped Ba–Sr based W type hexagonal ferrites for microwave absorption applications

The utilization of hexagonal structures in nano ferrites has been employed for absorption because of their dielectric, attenuation characteristics, and reflection losses. Electromagnetic pollution is one of the significant issues in cleaning the environment. Electronic devices produce pollution and are hazardous to human health. Therefore, ferrite materials have been used for absorption purposes. In this study, the impact of chromium substitution on the structural and dielectric specifications of the Barium-strontium-based W-type hexagonal ferrites has been investigated and used for microwave absorption application. The sol-gel auto-ignition process prepared w-type hexagonal ferrites with Ba0.5Sr0.5Mg2CrxFe16-xO27 (x = 0.0, 0.1, 0.2, 0.3, and 0.4). According to XRD examination, the formation of single-phase W-type hexagonal ferrites was proven. The synthesized composition is confirmed to be nanocrystalline because the calculated crystallite size value is in the nanometer range. FTIR analysis confirmed the structure of W-type hexagonal ferrite. Raman spectroscopic study examined the vibrational and rotational modes of molecules. Survey spectra of XPS, which include Ba, Sr, Mg, Fe, Cr, and O, confirmed the presence of all constituent elements. SEM analysis confirmed that the sample contains grains with a hexagonal platelet shape. The results showed that increasing chromium concentration reduced the dielectric permittivity, tan loss, and ac conductivity. At x = 0.4, the reflection loss value is very low. The recorded value is −79.62 dB, corresponding to a frequency of 5.92 GHz, with a thickness of 1.75 mm. Because of this, W-type hexagonal ferrites are suitable for a wide range of electronic applications, including microwave absorbers, high-density recording media, and multilayer chip inductors. These applications have made it possible to functionalize these materials in order to enhance device performance and lower the size, weight, and cost of devices while also fostering the development of new technologies that have significantly improved the quality of our daily lives.

Band–gap reduction of aluminum substituted M−type hexagonal ferrite to study its characteristics

The sol-gel auto-combustion approach was used to create a binary combination of Strontium aluminum chromium M−type hexaferrites at the iron site. The hexagonal phase and normal composition of prepared substances were confirmed through X-ray diffraction technique(XRD) and FT-IR spectroscopy. The structural investigation was evaluated using XRD, which determined crystalline size, lattice constants, miller indices, and cell volume. The production of hexaferrite is confirmed by FTIR measurement in all samples. The existence of metal-oxygen bonds on tetrahedral sites and also on octahedral confirms that all prepared samples exhibit M−type hexagonal ferrites. SEM study reveals the morphology of all prepared samples which gives the defined shape and boundary. The UV and Energy gap of all prepared samples were measured to analyze their absorption.

Evaluations of the structural, dielectric, and microwave properties of Pr-doped Ba2Co2Fe12−xPrxO22 (x = 0.0–0.1) Y-type hexaferrites for high frequency applications

Y-type hexagonal ferrite samples with chemical composition of Ba2Co2Fe12−xPrxO22 (x = 0.0, 0.025, 0.05, 0.075, 0.1) were prepared by sol-gel auto combustion technique. Physical and dielectric properties of all the hexagonal ferrites were evaluated. The single-phase hexagonal structure was identified without any impurities through XRD analysis. SSP Plot depicted the crystallite sizes ranging from 22.287 nm to 36.648 nm. The dielectric observations were estimated as a function of frequency (1–6 GHz), and the behavior of each sample was characterized using the theories of Maxwell-Wagner and Koop. Cole-Cole analysis was used to evaluate the conduction process in Pr doped Y type hexagonal ferrites. According to the reflection losses in samples, x = 0.025 is the best absorption material among all the synthesized compositions because of its smallest RL of − 67.75 dB at 4.11 GHz. In addition, Pr doped sample with (x = 0.075) shows RL of − 48.20 dB, − 50.32 dB, and- 43.64 dB at 0.25, 2.03, and 5.08 GHz, respectively. Pr doped Y-type hexagonal ferrite results suggested using and designing hexaferrite-based nanocomposite for high-frequency absorbers in the microwave region.

Sol-gel Synthesized Yb-substituted ?-type Hexagonal Ferrites: Study of Structural, Grain Morphology, Electrical Polarization, Electrical Resistivity, Magnetic and Permeability Properties

In present work, an investigation was carried out about the various important properties of Yb 3+ substituted Potassium based ?-hexaferrite KFe 11-x Yb x O 17 (x= 0.0, 0.02, 0.06, 0.1). The Sol-gel auto combustion technique was used to synthesize all the samples. The X-ray diffraction (XRD) patterns confirmed the single hexagonal phase for all prepared samples. The Scanning Electron Microscopy (SEM) confirmed the agglomeration of small particles into big grains. The DC electrical resistivity, measured in the voltage range of (-200V) to (200V), was observed to vary with Yb 3+ contents. The Polarization versus electric field loops revealed the lossy behaviour of pure and substitute samples which indicated the resistive nature of the samples. The saturation and remanence polarization first decreased and then increased with Yb 3+ substitution due to ferric ions distribution between octahedral sites and resistive nature of the samples, respectively. The samples exhibited peculiar magnetic behaviour with the substitution of Yb 3+ ions. The saturation magnetization was increased up to concentration x = 0.06 and then decreased with further substitution of Yb 3+ contents. The coercivity values varied in the range of 141.43 to 279.26 Oe for all the samples which confirmed the soft magnetic nature of present synthesized material. The real part (µ’) and imaginary part (µ’’) of permeability exhibited the high values at low frequencies and these values decreased with the increase of frequency. The prepared samples were supposed to be used as core material of transformer and in high frequency applications due to high resistivity value and low eddy current losses.

Investigation of structural, physical, spectral, photoluminescence, Raman, and dielectric properties of Ba2Co2GdxFe28-xO46 hexaferrites

Nano-crystalline Gd-substituted X-type hexaferrites with the composition Ba2Co2GdxFe28-xO46 (x = 0.00, 0.08, 0.16, 0.24, and 0.32) were synthesized using sol-gel auto-combustion procedure. The establishment of single and pure phases of X-type hexagonal ferrites is verified by X-ray diffraction. The crystallite size ranging from 25 to 31 nm showed the increasing trend with the enhancement of Gd-substitution. The unit cell volume was found in 2502.83–2516.07 Å3. The alteration in lattice parameters and cell volume is due to the difference in ionic radii of the host (Fe) and substituent (Gd) element. FTIR spectra ranging 590-3000 cm−1 revealed the emergence of specific absorption bands verifying the formation of hexagonal ferrites. The behavior of dielectric properties is frequency dependent. The dielectric constant at low frequency for all substitution was high, but over the large frequency values, the dielectric constant was decreased. The dielectric loss factor increases over low frequencies and decreases as frequency rises with a higher concentration level. Higher dielectric parameter values suggest that synthetic material might be good for high-frequency applications and super-capacitors fabrication. The changes in Raman spectra as a function of substitution content are ascribed to the development of strain in the unit cell (x). The XRD investigation well corroborates this conclusion. FESEM images depicted the hexagon shaped particles of the X type hexagonal ferrites. In the PL spectra of synthesized compounds, all emissions invisible (red) zone with PL intensity at 661 nm were observed.

Enhanced Structural and Dielectric Properties of Calcium and Chromium-Based M-Type Hexagonal Ferrites with Polyvinyl Alcohol (PVA) Polymer Composites

[Formula: see text]-type hexagonal ferrites with compositions Ca[Formula: see text]CrxFe[Formula: see text]O[Formula: see text] at ([Formula: see text], 0.2, 0.3, 0.4, 0.5) were successfully prepared by sol–gel auto combustion method and then immersed with polyvinyl alcohol (PVA) by ultrasound-assisted in situ emulsion technique. The results indicate that the synthesized nanoparticles were diffused homogeneously in PVA retaining the size and shape of the particle. The single-phase [Formula: see text]-type hexagonal structure was revealed by X-ray diffraction (XRD) with extra 101 peak of PVA at 2[Formula: see text]. The suitable signal-to-noise ratio in the high density recording media can be achieved due to the small particle size of the prepared composites as compared to pure hexaferrites. The interaction between PVA and nanoparticles was confirmed by Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) images revealed the homogeneous distribution of grains, the crystallite size was measured from SEM (25–38[Formula: see text]nm), and it is also in agreement as calculated from the Scherer formula. Dielectric properties were also explored in the range of 1 MHz–3 GHz frequencies. Dielectric constant and dielectric loss were found to decrease with increasing frequency and decrease with the addition of ferrite ratio in the polymer matrix. This impact is because of the grain boundary at low frequency regime. The occurrence of resonance at high frequency regime recommends the investigated samples for multilayer chip inductor.

Effect of calcination temperature on structural and magnetic properties of lightly lanthanum substituted M-type strontium cobalt hexaferrites

A series of M-type lanthanum substituted strontium cobalt hexaferrites, Sr0.5Co0.5LaxFe12-xO19 (x = 0.0, 0.05, 0.15 and 0.2) was synthesized using the simple heat treatment method. The synthesized hexagonal ferrites were calcinated at 950 °C and 1050 °C for 3 hrs in a muffle furnace and then slowly cooled to room temperature. X-ray diffraction (XRD) technique and magnetic hysteresis loops were used to investigate the structural and magnetic properties of prepared samples respectively. The X-ray diffraction analysis of all the samples shows the presence of M- type hexagonal ferrite and hematite phases. Room temperature magnetic hysteresis loops analysis shows the increase in saturation magnetization with the increase in lanthanum substitution.

SYNTHESIS AND CHARACTERIZATION OF COBALT SUBSTITUTED W TYPE HEXAGONAL FERRITES

In this work W type hexagonal ferrites with chemical composition Sr1-xCrxCo2Fe16O27(x= 0.0, 0.02, 0.04, 0.06, 0.08, 0.1) were synthesized by sol gel auto combustion method. Annealing of the samples was done at 1200 C for 8 hours. Structural and optical properties and grain morphology of the synthesized samples were studies through X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Ultraviolet visible spectroscopy techniques and scanning electron microscope (SEM). XRD analysis confirmed that all samples exhibited hexagonal W-type single phase crystalline structure at temperature range of 1200oC with no impurity phase. The estimated grain size from SEM images is in the range of 76-139 nm that confirms nanocrystalline structure of samples with hexagonal structure. The FT-IR spectral analysis exhibited that absorption band occurred in ranging from 450 cm-1 to 650 cm-1 . Evidence of successful formation of hexaferrites was revealed by FTIR spectra of prepared samples. The existence of metal oxygen bond at octahedral site and tetrahedral site confirms that all fabricated samples exhibit W-type hexagonal ferrites. Optical characteristic of Sr1-xCrxCo2Fe16O27 analyzed by UV-Visible spectroscopy. The absorption spectra of synthesized nanoparticles of W-type recorded in range of wavelength 300 to 800 nm. This spectroscopy is significant in exploration of materials electronic properties. W-type hexagonal ferrites are suitable for high frequency application such as microwave devices.

Tuning the structural, magnetic and multiferroic properties of Sm3+ substituted barium hexaferrites BaFe12-xSmxO19 nanoceramics

Abstract M- Type hexagonal ferrites BaFe12-xSmxO19 with (x = 0.0, 0.25, 0.50, 0.75, 1.0) is prepared using citrate precursor based sol–gel method. The X-ray diffraction pattern confirms phase purity of the samples. All samples possessed hexagonal crystal symmetry belonging to P63/mmc space group. The Williamson-Hall plot is utilized for calculating crystallite size and lattice strain present in prepared samples. The strain reaches to a maximum value 1.58 × 10−3 for BaFe11Sm1O19. W-H plot calculations are supported by SEM morphological analysis. Lattice parameters shows noticeable increments due to induced lattice strains in samples. FTIR spectral analysis is in agreement with the XRD results. The magnetic parameters of prepared samples gets refined with samarium substitution with appreciable Magnetization 42.62–63.05 emu/g and Retentivity 19.73–29.26 emu/g. Coercivity value increased from 303.5 to 2265.1 Gauss. The Magnetocrystalline anisotropy (K1) is calculated using Law of Approach to Saturation, which ranges from 1.37 to 4.24 × 106 erg/cm3. Further the ferroelectric properties are evidently observed in Sm3+ doped BaFe12-xSmxO19 nanoceramics, with Remanance polarization (Pr) and Coercive polarization (Pc) of 6.1 μC/cm2 and 6.5 kV/m respectively. The FeO6 octahedron in its perovskite-like hexagonal unit cell and off centering of Fe3+ from the center of octahedron is suggested to generate polarization in doped samples. Therefore a correlation between lattice strain mediated structural, magnetic and multiferroic properties enrichment with varying samarium content in hexaferrite lattices is explored in this article.

Synthesis and Characterization of Aluminium and Cobalt substituted W type Hexagonal Ferrites

Our work utilized sol-gel auto combustion method for M-type ferrites synthesis with hexagonal orientation having chemical composition Ca (1-X) AlXCo2Fe16O22. Annealing of the samples was performed for 8 hours at 1200oC. Structural properties and grain morphology of the synthesized samples included X-ray diffraction (XRD), Fourier transforming infrared spectroscopy (FTIR), Ultraviolet visible spectroscopy techniques and scanning electron microscope (SEM). The XRD analysis verified that all samples exhibited single-phase crystalline hexagonal w-type structure at a temperature range of 1200oC without impurity level. The approximate grain size from SEM images is within the range of 76-139 nm, which confirms nanocrystal line structure of hexagonal samples. The spectral analysis of the FT-IR showed that the band of absorption ranged from 450 cm-1 to 650 cm-1. FTIR spectra of prepared samples disclosed proof of positive formation of hex ferrites. The presence of metal oxygen bonding at octahedral site and tetrahedral site indicates that all manufactured samples show hexagonal ferrites w-type hexagonal ferrites are ideal for application with high frequency applications, such as microwave systems.

Structural, physical and magnetic evaluations of Ce-Zn substituted SrCo2 W-type hexaferrites prepared via sol gel auto combustion route

SrCo2 W-type hexagonal nanoferrites with composition SrCo2-xZnxCeyFe16-yO27 (whereas x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 and y = 0, 0.02, 0.04, 0.06, 0.08, 0.1) were synthesized by sol-gel auto combustion method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM) and Vibrating sample magnetometer (VSM) were used to find out the structural, vibrational, morphological and magnetic properties of SrCo2 W-type hexagonal ferrites. Physical properties such as bulk density (Dbulk), X-ray density (Dxrd) and porosity (%P) of the SrCo2 W type hexagonal ferrites samples were calculated. Bulk density of the samples decreased whereas X-ray density increased with the Ce-Zn substitution in the W-type ferrites. Single phase samples of all the nanoferrites are achieved at the sintering temperature of 1050 °C. Structural parameters such as lattice parameters ‘a’ and ‘c’ were also calculated. Lattice parameter ‘a’ is found to be increased whereas ‘c’ is found to be decreased with the substitutions. Force constants at tetrahedral and octahedral sites are also evaluated which confirm the phase and substitution in W-type hexagonal ferrite. FESEM images showed homogenous and well crystallized at higher substitution of Ce-Zn in SrCo2 W-type hexagonal ferrites. Detailed magnetic parameters such as magnetic remanence coercivity, saturation, Bohr magneton, initial permeability, magneto crystalline anisotropy constant (K) and magnetic field anisotropy (Ha) were measured. Magnetic remanence decreased whereas coercivity, magneto crystalline anisotropy and field anisotropy increased in the SrCo2 W-type hexagonal ferrites samples. The dependence of Hc and Ha on the SrCo2 W-type hexaferrites may be due to the variations in the K and Ms of the substituted samples. Therefore, the prepared SrCo2 W-type nanoferrites with appropriate amount of metal cations are suitable candidate for the microwave devices and high frequency applications.

Influence of Mg substitution on structural, magnetic and dielectric properties of X-type barium[sbnd]zinc hexaferrites Ba2Zn2-xMgxFe28O46

Mg substituted X–type hexagonal ferrites with the chemical composition Ba2Zn2-xMgxFe28O46 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were successfully synthesised by a sol–gel auto–combustion technique, in order to investigate the effect of Mg substitution on structural, magnetic and dielectric properties. XRD analysis of prepared samples revealed the formation of pure X–type phase. The variations (decreasing trend) in lattice parameters with Mg substitution indicate the incorporation of Mg substitution into the crystal structure. The average crystallite size of heated powders was found to be in the range of 16–22 nm. For the first time, the RT hysteresis loops of Ba2Zn2Fe28O46 (Zn2X), Ba2Mg2Fe28O46 (Mg2X) and Ba2Zn2-xMgxFe28O46 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were measured. The saturation magnetisation showed an initial decrease with x = 0.4 − 1.2, and then an increase with x > 1.2, to the largest final values of 63.29 A m2 kg−1 for the fully Mg–substituted x = 2.0. The value of coercivity lies in the range of 89.9–209.3 kA m−1 (1130–2630 Oe), and the magnetic results suggest that the compositions x = 0.0, 0.4 and 1.2 possess multi-domain microstructures, while x = 0.8, 1.6 and 2.0 possess single domain microstructures. The room temperature Mӧssbauer spectra were analysed with six sextets of five magnetic sublattices, and the results are presented as a function of Mg substitution. It was found that initial levels of Mg substitution reduce the Fe populations at a and b (spin up) sublattices, but that with x > 1.2 these become repopulated at fIV (spin down) site, resulting in an increase in magnetisation. Dielectric parameters such as dielectric constant and loss factor were studied as a function of frequency, and results show normal behaviour for ferrimagnetic materials. At low frequencies (100 Hz–2 MHz), relative permittivity was constant between 0.3 and 1.5 above 20 kHz, with the higher values belonging to the more dense samples. All Mg substituted samples had lower losses above 20 kHz than the pure Zn2X. In complex measurements at microwave frequencies (500 MHz–13.5 GHz), all samples had a real permittivity of around 7.5, except for the fully Mg–substituted sample (x = 2.0), which had a lower ε′ of 5.5. For two samples (x = 0.4 and 1.6) we observed dielectric resonances between 12.85 and 13.25 GHz. All showed a steady real permeability of around 1.2–1.5 over the whole 1–13 GHz range, and ferromagnetic resonance (FMR) between 1 and 5 GHz, and ∼12.5 GHz.

中性子回折と放射光によるLa-Co置換フェライトの局所構造解析

The La-Co substituted magnetoplumbite type (M-type) hexagonal ferrites are known to have the higher magnetic crystalline anisotropy compared with conventional M-type Sr ferrites. The site occupation of cation in the crystal structure has been analyzed by neutron diffraction and EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy in order to clarify the correlation between the local structural change and the improvement of the magnetic anisotropy. The EXAFS analysis has suggested that Co ions were located in the 4f1, which showed good agreement with the results by neutron diffraction and XMCD analysis.

Microstructures and High Frequency Properties of ${\hbox{Sm}}^{3+}$ Doped ${\hbox{Co}}_2{\hbox{Z}}$-Type Hexagonal Ferrites as Anti-EMI Magnetic Bead Materials

The Sm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> doped Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Z-type hexagonal ferrite materials were prepared by conventional ceramic method and characterized by techniques such as X-ray diffractometer and scanning electron microscopy. The influence of a small amount of Sm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> addition on structures and magnetic properties of the materials was investigated. The results show that Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Z-type hexaferrite is still in the main phase of the Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Z ferrite materials doped with Sm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> . It is observed that Sm-rich phase with granular morphology is dispersed in the main phase. The hysteresis measurement indicates that the specific saturation magnetization of Sm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> doped sample is bigger than that of the undoped one. The addition of Sm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> in Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Z ferrite can decrease the real part μ' and the imaginary part μ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">''</sup> of complex permeability, but increase significantly the cutoff frequency. The Sm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> doped Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Z ferrites sintered at 1250°C exhibited excellent high frequency properties such as high cutoff frequency above 1.8 GHz and higher initial permeability up to 5.

Magnetic Properties of Poly (Divinylbenzene, Ethylene Glycol Dimethacrylate and Vinyl Alcohol) Containing Barium Ferrite Nanoparticles

Three di erent kinds of polymer lms, poly (divinylbenzene), poly (ethylene glycol dimethacrylate) and poly (vinyl alcohol), containing M -type hexagonal barium ferrites (BaFe12O19) were synthesized on glass substrates by using surface polymerization method. The structural properties were characterized by X-ray di raction and atomic force microscopy. X-ray di raction patterns show that polymer lms have a polycrystalline structure. The magnetic measurement of polymer lms were examined at room temperature using vibrating sample magnetometer and magnetic force microscopy, respectively. The magnetic measurements indicate that P(VA)-BF lms exhibit higher saturation magnetization and coercive eld than P(EGDMA)-BF and P(DVB)-BF lms.

Effect of Ni-Stearate Addition on Magnetic Properties of Anisotropic BaFe2 W-type Ferrites

An experiment was carried out to investigate the effect of Ni-Stearate as a reducing agent on the magnetic and physical properties of anisotropic BaFe2-W type ferrite magnets. It was found that the magnetic properties of BaFe2-W type hexagonal ferrite were improved by adding 0.5 wt% of Ni-Stearate, 0.5 wt% of SiO2, and 0.5 wt% of CaO together. The optimum conditions for making magnets were as follows; Chemical composition: BaO · 8.5Fe2O3, semisintering condition: 1350°C×4.0 h in nitrogen gas atmosphere, drying condition: 190°C×2.0 h in air, sintering condition: 1180°C×1.5 h in nitrogen gas atmosphere. Magnetic and physical properties of a typical sample were Jm=0.47 T, Jr=0.42 T, HcJ=203.5 kA/m, HcB=192.3 kA/m, (BH)max=31.5 kJ/m3, Tc=484°C. The lattice constants of this compound were a=5.905×10-10 m, c=32.62×10-10 m, and c/a=5.523.

Magnetic Properties of Gd and Tb Doped Co 2Z Type Hexagonal Soft Magnetic Ferrites

The Gd and Tb doped Co 2Z type hexagonal ferrite materials were prepared by the conventional ceramic method. The results showed that the Co 2Z ferrite materials doped with a small amount of Gd and Tb presented still the single phase of Co 2Z planar hexagonal structure. The real part μ' of the samples increased significantly, but cut-off frequency of the ferrites went down. The Tb doped Co 2Z ferrites sintered at 1150 °C exhibited excellent high frequency properties such as high initial permeability up to 8 and high cut-off frequency more than 1.8 GHz. Apparently, it was of benefit to the application of the materials. With the increasing of sintering temperature, the real part μ' of complex permeability increased and cut-off frequency want down.

Design, fabrication and characterization of hexagonal ferrite multi-layer microwave absorber

Ba(Co,Zn) 2-W type hexagonal ferrites, prepared by a citrate sol–gel method have been used as fillers in five layers of chlorosulphonated polyethylene matrix composite. Adding an outer layer with carbonyl iron filler, a thin quasi-double-layer microwave absorber has been fabricated, that exhibits reflection loss (RL)<−12 dB at 5–12 GHz with a broad minimum of −18 dB at 7.5–9.5 GHz. Layer succession has been optimized for 2 mm total thickness and minimum RL at the X-band, by means of a model based on the transmission line theory, with the actual permittivity ε and permeability μ of the layers as input parameters. This approach has permitted the optimum use of hexagonal ferrites with varying electromagnetic properties.

The role of Mg substitution on the microstructure and magnetic properties of Ba Co Zn W -type hexagonal ferrites

A series of W-type hexagonal ferrites with the composition BaCoZn 1− x Mg x Fe 16O 27 (0⩽ x⩽0.6) were prepared by the conventional ceramic method to study their structural and magnetic properties as a function of temperature and composition. The characterization using X-ray diffraction indicated that a hexagonal W-type single-phase structure and the effect of composition on the unit cell parameters, density and porosity was studied. The variation of the magnetic susceptibility ( χ M) with temperature for all the investigated samples in the temperature range (300–800 K) shows three regions of behavior that was explained on the basis of the distribution of Zn 2+ and Mg 2+ ions in the lattice and leads to the anomalous behavior of the effective magnetic moment μ eff. The Curie temperature indicated that the critical concentration is at x=0.5. Paramagnetic nature of the samples above the Curie temperature is observed. The Curie Weiss constant θ calculated from the plot of 1/ χ M vs. T (K) is in agreement with the expected value. The effective magnetic moment μ eff decreases with increasing the intensity of magnetic field. The possible mechanisms contributing to these properties are discussed in the text.