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In the recent decade, advancements in technology and the excessive use of electronic devices in everyday life have harmed human health and produced electromagnetic pollution. To overcome these problems, hexagonal ferrites are used as excellent microwave-absorbing materials to clean the environment and protect human health. In this study, chromium (Cr3+) substituted Y-type BaSrCo 2 Cr x Fe 12-x O 22 hexaferrites (x = 0.0, 0.5, 1.0, 1.5, and 2.0) have been synthesized through self-ignited sol-gel method and sintered at 1150 °C for 5.5 h. The single phase of the synthesized nanomagnetic materials was confirmed by X-ray diffraction analysis. FTIR analysis unfold the Fe–O vibrational bands at tetrahedral and octahedral sites due to iron oxide base material. The incorporation of Cr3+ limits the transfer of electrons. As a result, DC electrical resistivity significantly increases from 7.59 × 109–4.85 × 1010 (Ω cm). The dielectric behavior and impedance analysis was carried out in the 1 MHz - 6 GHz range. By replacing Cr3+, the dielectric constant and loss exhibit a decreasing behavior. For all compositions, the values of reflection loss are calculated in the range of −39.37 to −32.95 to make them excellent microwave-absorbing materials due to their lower cost, small size, and lightweight properties. The substitution of Cr3+ increases the saturation magnetization (61.35–96.10 emu/g), coercivity (62.31–897.99 Oe), and remanence (12.30–46.52 emu/g). An increase in the coercivity value indicated that samples are thermally stable and suitable for perpendicular magnetic recording media. [ABSTRACT FROM AUTHOR]

Nickel substituted Sr–Co nano spinel ferrites with composition Sr 0.5-x Ni x Co 0.5 Fe 2 O 4 (0.0, 0.1, 0.2, and 0.3) were prepared with the help of a sol-gel auto combustion route. The prepared materials were sintered at 800 for four and a half hours. Analysis of XRD confirmed that the material is composed of a cubic spinel structure with a single phase, and its space group is Fd-3m. Rietveld refinement of X-ray diffraction data was done for all prepared compositions using FULLPROF software. As the composition under study contains more nickel than lattice constant, crystalline size, X-ray density, and bulk density decrease. The dielectric properties were observed about frequency. The dielectric properties revealed that dielectric loss, dielectric constant, and ac conductivity decrease with increasing the Ni2+ content. The activation energy (ΔE) was calculated from the slope of Arrhenius plots. The ΔE found in the range of 0.580–0.096 eV. The analysis of XPS was carried out to examine the elemental state of annealed samples. The prepared material is suitable for employment in applications involving high frequencies because the Ni-doped Sr–Co ferrites with the greatest Ni2+ concentration have the lowest dielectric loss, dielectric constant, and tangent loss value. [ABSTRACT FROM AUTHOR]

Y-type hexaferrite ceramic materials of nominal composition Ba 2 Co 2 Cr x Y x Fe 12-2x O 22 (x = 0.00, 0.03, 0.06, 0.09, and 0.12) were synthesized by sol-gel auto combustion route. Y-type hexaferrites are technologically important ceramic materials for fabricating modern electronic devices and microwave absorbers due to their unique electrical and dielectric properties and reflection loss behavior. XRD classifies the single-phase formations with space group R 3 ‾ m. The crystallite size of the synthesized samples was calculated in (34–41) nm range. The specific absorption band in FTIR spectra approves the (Fe–O) stretching vibrations at wavenumbers 446 and 478 cm−1. The substitution of iron by Cr3+ and Y3+ increases DC resistivity from 1.03 × 1011 to 1.17 × 1012 Ω cm by limiting the electrons jumping between ferrous and ferric ions. The activation energy and drift mobility were also calculated among the substituting content of Cr3+-Y3+. The dielectric response in 1 MHz–6 GHz frequency was determined and the effect of substitution has been observed. The Maxwell-Wagner (MW) bilayer model is used to study dispersion in dielectric parameters with reference to applied frequency. The maximum values of dielectric losses were obtained at 6 GHz in the range of 0.37–0.60. The coercivity values confirms the soft magnetic nature of synthesized samples. The microwave absorption (MW) properties of synthesized materials were improved upon Cr3+-Y3+ substitution. Minimum reflection loss R Lmin = −66 dB (99.99% absorption of MW) at 1.46 GHz frequency and 1.96 mm thickness was obtained for x = 0.09 composition. All investigated samples are efficient materials for stealth technology, radar cross-reduction, EM interference shielding, and high-frequency applications. [ABSTRACT FROM AUTHOR]

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 Ba 0.5 Sr 0.5 Mg 2 Cr x Fe 16-x O 27 (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. [ABSTRACT FROM AUTHOR]

The impact of Cr3+ substitution on the electrical and dielectric properties of Y-type hexaferrites with composition Ba 2 Mg 2 Cr x Fe 12-x O 22 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) was synthesized by the sol-gel auto combustion technique. The lattice parameters 'a' and 'c' slightly increase with the substitution content of Cr3+, and some other physical parameters, including porosity, microstrain, dislocation density, specific surface area, and stacking fault coefficient, were determined from XRD data. FTIR spectra confirm the formation of iron oxide base material by the appearance of three signature bands at precisely 429, 474, and 499 cm-1 due to Fe–O vibrations at octahedral and tetrahedral sites. Substituting Cr3+ at the octahedral site enhanced the room temperature DC electrical resistivity from 6.89 × 109 to 2.27 × 1010 Ω-cm. Temperature-dependent DC electrical resistivity exhibits semiconducting behavior. There is a direct relation between resistivity and activation energy. The dielectric behavior of Cr3+ substituted samples in the frequency range of 1 MHz–6 GHz was understood based on the conduction mechanism through the hopping of electrons between Fe3+ and Fe2+ ions and the Maxwell-Wagner Model. In impedance spectroscopy studied using Cole-Cole plots, most dielectric response arises from the contribution of the grain boundary effect. With the substitution of Cr3+, dielectric losses decreased. A very high Q-value around 1 GHz was observed, suggesting that these hexaferrites are efficient materials for many high-frequency applications, such as multi-layer chip inductors (MLCI), dielectric resonators, and power applications. [ABSTRACT FROM AUTHOR]

Polycrystalline Cr3+ substituted Ba 4 Zn 2 Fe 36-x Cr x O 60 (Zn 2 U) U-type hexaferrite compositions Ba 4 Zn 2 Fe 36-x Cr x O 60 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were fabricated using the sol-gel self-ignition technique. U-type hexaferrite structure was achieved by sintering the powdered samples for 6 h at 1200 °C in a muffle furnace. The phase identification and structural parameters of Zn 2 U hexaferrites were evaluated by X-ray diffraction peaks of the powdered samples. Lattice parameters (a,c) and unit cell volume decreased upon Cr3+ substitution. The crystallite size was measured between 61 and 57 nm. FTIR spectra revealed the existence of specific absorption (Fe–O) bands at wavenumbers 419 and 539 cm−1. These bands further verify the formation of U-type hexaferrite. SEM micrographs showed the platelet-like morphology of the grains with proper hexagonal structure. X-ray photoelectron spectroscopy (XPS) results confirmed the existence of all metal ions with their corresponding electronic states. The dielectric response of the fabricated Zn 2 U U-type hexaferrite pellets was investigated at room temperature through a vector network analyzer with a wide frequency band from 1 MHz to 6 GHz. Dielectric constant (εʹ) was increased for the compositions x = 1.0 and 1.5 while dielectric loss (εʺ), tangent loss (tanδ), and ac conductivity (Ϭ ac) were reduced upon Cr3+ substitution. Single semicircles in the impedance Cole-Cole plots revealed that grain boundaries play a vital role in the conduction process of prepared U-type hexaferrites. Microwave absorption (MW) was improved with Cr3+ substitution. The minimum reflection loss (R L) of −53dB (99.99% MW absorption) at frequency 1.3 GHz was obtained for composition x = 0.5. The dielectric analysis (low losses and high Q-values) of the prepared hexaferrites predicts their appropriate use in high-frequency device applications. [ABSTRACT FROM AUTHOR]

Technology important ferrites ceramic Sr 2 Ni 2 Ga x Fe 12-x O 22 (x = 0.00, 0.2, 0.4, 0.6, and 0.8) samples were produced using sol-gel auto combustion route. Structural, electrical, dielectric, and magnetic parameters were identified by substituting Ga3+ at the Fe3+ site. It was recognized that an increase of Ga3+ content in (Sr 2 Ni 2 Ga x Fe 12-x O 22) ceramic samples first decreased, then increased lattice parameters, and the density of samples was observed. This is because of the ionic radii and atomic weight of Ga3+ and Fe3+ cations. FTIR spectra show two characteristic absorption bands at 444-513 cm−1 caused by metal-oxygen vibrations. Due to the contribution of smaller grains of samples, the higher values of resistivity were observed, which vary from 3.78 × 1010 (Ω cm) to 1.13 × 1011 (Ω cm) by the substitution of Ga3+ ions at the octahedral site. The activation energy was measured between 0.20 and 0.61 eV. The dielectric response of Ga3+ substituted ferrite ceramic samples were studied in the 1 MHz-6 GHz frequency region. The Maxwell-Wagner bilayer model studied the effect of polarization with applied frequency on dielectric parameters. With the substitution of Ga3+, minimal losses in the range 0.34–0.44, about 6 GHz, and a high Q-value of about 10,000 were observed for each sample. In impedance spectroscopy analysis Cole-Cole plots confirm that the dielectric response is because of the influence of grain boundaries. The substitution of Ga3+ enhances saturation magnetization (68.20–71.78 emu/g) while coercivity decreases (655.86–507.86 Oe). In the present finding, the low dielectric loss, moderate permittivity, high value of the Quality factor, and very high value of resistivity of about 1.13 × 1011 that reduces the eddy current losses suggested that these materials are appropriate candidates for many high-frequency applications such as multilayer chip inductor, dielectric resonators, power applications, and microwave devices. [ABSTRACT FROM AUTHOR]

Sol-gel auto-combustion process was used to synthesize M-type hexagonal ferrite powder samples with the chemical formula Ba 0.3 Sr 0.7-x Co x Fe 12-y Sm y O 19 (x = 0–0.5, y = 0–0.05). The samples were examined using the X-ray diffraction technique (XRD), Raman, and photoluminescence spectroscopies. M-type phase with a hexagonal structure was obtained along with the single peak of the impurity phase (α-Fe 2 O 3). The samples' lattice parameters, crystallite size, volume, X-ray density, bulk density, porosity, dislocation density, and micro strain were also calculated from XRD data. Raman spectroscopy detected all the associated vibrational and rotational modes in the samples. Changes in Raman spectra versus levels of substitution of Sm and Co concentrations are linked to the variation of strain in the unit cell. All emissions were visible (red) in the Photoluminescence (PL) spectra, which had a wavelength close to 661 nm. The materials are semiconducting with bandgap energy E g = 1.875 eV. The results show the samples are beneficial for microwave and high-frequency applications. [ABSTRACT FROM AUTHOR]

Nano-crystalline Gd-substituted X-type hexaferrites with the composition Ba 2 Co 2 Gd x Fe 28-x O 46 (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. [ABSTRACT FROM AUTHOR]

BaMg 2 Tb x Fe 16-x O 27 (x = 0.00, 0.04, 0.08, 0.12 and 0.16) hexaferrites have been synthesized by sol-gel auto combustion method. The synthesized hexaferrites were characterized by structural, spectral, and dielectric properties. As the ionic radii of substituted element Tb3+(0.93 Å) is higher than Fe3+ (0.64 Å), the lattice parameter 'a' increase with substitution while the lattice parameter 'c' decreases due to internal stresses and lattice distortion. Crystallite size of Tb3+ substituted W-type hexagonal ferrites are calculated and found in the range of 13.2–14.95 nm. FTIR patterns confirm the presence of Fe–O bands at octahedral and tetrahedral sites. The variations in the band positions were observed with substitutions of Tb3+ content. It is also observed that values of both force constants (K o and K t) increase with the inclusion of Tb3+ ions, showing the strong intermolecular bonding. The different parameters of dielectric characteristics were examined in the frequency range 1 GHz–6 GHz, and these showed variation with Tb3+ incorporation and frequency. Dielectric constant, dielectric loss factor, tan loss, and ac conductivity showed an increasing trend while Z′ and Z″ decreases with frequency because conductivity increased. Q value of these materials is low, which may be used in resonant frequency ferrites bead. The obtained results of all parameters including large value of dielectric parameters suggested that these prepared hexaferrites can be used in microwave frequency attenuating devices at GHz, recording, and storage media, and electrical components in mobile phones and refrigerator magnets. [ABSTRACT FROM AUTHOR]

Ba 0.6 Sr 0.4-x Yb x Fe 12-y Co y O 19 , (0.0≤x ≤ 0.125, 0.0≤y ≤ 1.25) M-type hexaferrite were synthesized using the auto combustion sol-gel process. The synthesized samples were then sintered at 1200 °C for 5 h in a muffle furnace. XRD, FTIR, Raman, and Photoluminescence spectroscopies were used to analyse all the samples. XRD technique was used for structural examination of Ba 0.6 Sr 0.4-x Yb x Fe 12-y Co y O 19. The XRD patterns of Yb–Co co-substituted M-type hexaferrites revealed the pure single phase of synthesized samples. Change in Yb–Co concentration influenced lattice parameters and unit cell volume. The variations in lattice constants "a" and "c" values are 5.891–5.862 and 23.180–23.317. FTIR spectroscopic data graphs revealed the formation of several absorption bands from 430 cm−1 to 3000 cm−1. The strain in the unit cell produced by substitution changes in Raman spectra which is also confirmed by XRD. Many 630 nm–700 nm emissions were observed in the PL spectra of Ba 0.6 Sr 0.4-x Yb x Fe 12-y Co y O 19. Furthermore, a bandgap of 1.961–1.875 eV was observed for the pure sample. The substitution improves the dielectric losses and Ac conductivity. The Maxwell-Wagner theory was used to investigate the changing trends of characteristics regarding dielectric parameters. The findings show that the samples with the appropriate cationic substitution can be used in microwave and high-frequency applications. [ABSTRACT FROM AUTHOR]

A series of (Zr–Co) substituted Y-type polycrystalline hexaferrite with composition SrBaNi 2 (ZrCo) x Fe 12-2x O 22 (x = 0.0, 0.25, 0.50, 0.75, 1.0) were fabricated by sol-gel auto combustion method. Pure Y-type single phase formation was achieved at a relatively lower temperature of 1150 °C for 5:30 h. The fabricated nano ferrites were examined by X-ray powder diffraction to confirm the pure single-phase formation of Y-type hexaferrites. An increase in lattice parameters (a& c) was observed by adding Zr4+-Co2+ metal cations. Crystallite size (D) measured in the 48-19 nm range. FTIR spectra clarified iron-oxygen vibrational bands at 417-487 cm−1, which approved the Y-type hexaferrites formation. DC electrical resistivity has an opposite trend at high and low temperatures with increasing Zr4+-Co2+ content (x). DC electrical resistivity values depend on grain size; they have an inverse relation. Activation energy, drift mobility, and Curie temperature were also determined. Conduction is due to the hopping of electrons below the Curie temperature, and polarons are responsible for hopping above the Curie temperature. Activation energy varies from 0.39 to 0.10 eV with the substitution of Zr4+-Co2+ ions. A wide frequency range of dielectric characteristics (1 MHz–6GHz) was observed, and these parameters revealed a considerable fluctuation with the substitution of Zr4+–Co2+ ions. Dielectric constant, dielectric loss and ac conductivity of nano ferrites materials increased with frequency and Zr4+-Co2+ content (x). Complex impedance spectroscopy formalism using the Cole-Cole plots indicated that most dielectric responses arise from grain boundary contributions. [ABSTRACT FROM AUTHOR]

Enhanced magnetic and ferroelectric properties have been observed in Hf substituted Bi0.97K0.9Fe1−xHf(3/4)xO3 (0.00 ≤ x ≤ 0.20) nanocrystalline multiferroics which were synthesized via auto combustion sol–gel method. Citric acid was used as a solvent. Structural investigation confirmed the development of pure perovskite rhombohedral distorted phase. The enlargement in cell volume was observed with K–Hf substitution due to lattice distortion and the ionic radii of substituents. Ferroelectric loops showed that maximum polarization (Pmax) was inclined from 0.000376 to 0.391 µc/cm2 as well as remanent polarization (Pr) from 1.000815 to 5.39 µc/cm2. This was due to Hf–K contents which altered Fe–O bond length and increase disturbance in FeO6 octahedra which increase polarization. High values of saturation magnetization (Ms = 4.79 emu/g) and remanent magnetization (Mr = 1.7 emu/g) was attributed to disturbance in antiferromagnetic spin modulated cycloid (λ = 62 nm) structure. Enhancements of magnetic properties along with the formation of P-E loops make these multiferroic nanomaterials the best candidates for magnetoelectric RAMS. [ABSTRACT FROM AUTHOR]

The structural and dielectric properties of Gadolinium substituted U-type hexaferrites (Sr 4 Zn 2 Fe 36 O60) were investigated. The samples were synthesized via the Sol-gel auto combustion route. In a muffle furnace, these samples were sintered for 5 h at 1250 °C. The pellets of synthesized powder samples were characterized by XRD, PL, Dielectric, FTIR, and Raman spectroscopies. Structural elucidation of Sr 4 Zn 2 Fe 36-x Gd x O 60 was done via XRD. The obtained XRD patterns were matched with the prior literature. The impact of Gd3+ substitutions was measured on all the lattice parameters. Lattice constants "a" and "c" were found between 5.871 and 5.900 Å and 111.76–112.23 Å, respectively. The PL spectra of Sr 4 Zn 2 Fe 36-x Gd x O 60 demonstrated multiple emissions in the range of 630 nm–700 nm, and by analyzing PL spectroscopic results, a bandgap of 1.8742 eV was found for the un-doped sample. Many dielectric parameters, i.e., Dielectric constant (ε'), Dielectric losses (ε''), Loss tangents (tanδ), Complex electric modulus (M' & M″), and A.C conductivity (σ ac) were investigated at room temperature by changing the frequencies from 1 GHz to 6 GHz. The varying trends of dielectric parameters were analyzed with the assistance of the Maxwell-Wagner model. Various absorption bands were observed in the range of 500–4000 cm−1 by plotting the FTIR spectroscopic results of Sr 4 Zn 2 Fe 36-x Gd x O 60. Raman spectra demonstrated a combination of strong and fragile peaks in 1–1800 cm−1. The obtained results of various spectroscopies suggested that the prepared materials can be used extensively for different Micro-Wave attenuation purposes. [ABSTRACT FROM AUTHOR]

Gadolinium (Gd) and cobalt (Co) substituted Sr–Ba–Cu-based Y-type hexaferrites were synthesized with the help of the sol–gel auto-combustion route. XRD (X-ray diffraction) analysis was done to ratify the phase formation of hexaferrites. The impact of Gd3+ substitutions was measured on all the lattice parameters. Lattice constants “a” and “c” were found between 5.879–5.891 Å and 43.185–43.620 Å, respectively. It was observed from the XRD analysis that with an increase in Gd–Co contents, the enhancement in the average crystallite size is noted. The thermal decomposition process was studied using TGA (thermogravimetric analysis), revealing that the precursor may give the ending product when annealed over 850 °C. Various absorption bands were observed in the range of 350 to 1800 cm−1 by plotting the FTIR spectroscopic results of Gd–Co-substituted SrBaCu2Fe12O22 ferrites. The tetrahedral and octahedral sites indicated absorption bands via Fourier transform infrared spectroscopy (FTIR) spectra. An impedance analyzer was employed to explore the dielectric trend and AC conductivity of prepared nano hexaferrites. All prepared samples indicated dielectric dispersion, the usual dielectric behavior showing Maxwell–Wagner-type interfacial polarization. A decrease in dielectric constant and dielectric loss was found when the frequency was enhanced. Gd inclusion enhanced AC conductivity. Complex impedance analysis revealed semi-circles. With the enhancement in Gd–Co substitution the decrement in saturation magnetization (Ms) from 37.84 emu/g to 25.39 emu/g was observed, the rise of remanence (Mr) from 12.80 emu/g to 19.56 emu/g, and coercivity (Hc) from 1226.77 Oe to 5158.57 Oe was found. Therefore, the synthesized Sr–Ba–Cu-based Y-type hexagonal ferrites with the appropriate amount of Gd–Co substitution are suitable candidates for permanent magnetic materials and recording media. [ABSTRACT FROM AUTHOR]

Nano-crystalline Gd–Co substituted X-type hexagonal ferrites having formula SrBaMn 2-x Co x Gd y Fe 28-y O 46 (where x = 0–1, y = −0.1) were synthesized employing sol-gel route. X-ray diffraction technique verified the formation of pure phase X-type ferrites for all samples. Crystallite size was reduced from 27.49 to 24.52 nm with Gd–Co concentration, which is favorable for attaining an appropriate signal-to-noise ratio in electronic devices. Lattice constants (a, c), bulk, and X-ray density slightly increased owing to the large ionic radius and density of Gd3+ ions than Fe3+ ions. Fourier transform infra-red spectroscopy displayed absorption bands in the lower wavenumber range (482-584 cm−1). The higher absorption bands (482-584 cm−1) are due to metal-oxygen vibration octahedral and tetrahedral sites. The influence of Gd–Co on dielectric properties such as dielectric constant, tangent loss, ac conductivity, and Q-value on frequency and composition were investigated in the frequency region of 1 MHz–3 GHz. The incorporation of Gd–Co resulted in the enhancement of dielectric properties of as-prepared X-type materials desired in electromagnetic devices operating at microwave frequencies. Electric modulus analyses indicated the contribution of grain boundary towards resistance. [ABSTRACT FROM AUTHOR]

In present research six samples of nano X-type hexagonal ferrites with general formula SrBaMg2-xCoxDyyFe28-yO46 (x = 0–1; y = 0–0.1 with step size of 0.2 and 0.02, respectively) were synthesized by sol–gel technique. The temperature required for the phase formation of these materials was estimated using thermogravimetric analysis. X-ray diffraction patterns revealed the pure phase of the prepared materials up to the doping concentration of x = 0.4, y = 0.04 along with the second phase for higher doping concentration. The secondary phase appeared due to the solubility limit of higher ionic radius Dy3+ ions into the hexagonal lattice. The mean crystalline size decreased from 29 to 18 nm while unit cell volume, bulk density, and X-ray density were increased with Dy-Co doping. Hysteresis loops showed that by incorporation of Dy-Co ions the saturation magnetization (Ms) was enhanced from 50 to 60 emu.g−1. Also, coercivity (Hc) varied in the range 1573–3251 Oe, such high values of Ms and Hc propose the utilization of these X-type materials as permanent magnets and perpendicular recording media. The dependence of dielectric parameters (dielectric constant, ac conductivity, Q-value) on frequency (1 MHz–3 GHz) as well as composition was discussed. Inclusion of Dy-Co in X-type lattice modified dielectric parameters i.e. dielectric constant, ac conductivity was increased. Complex modulus studies directed to elucidate Nyquist plots which exhibited a single half-circle for all X-type ferrites, thus depicting Debye sort of behavior. [ABSTRACT FROM AUTHOR]

Ho-substituted Li–Ni ferrites with composition L i 1.2 Ni 0.4 Ho x Fe 2- x O 4 ; 0≤ x ≤ 0.15 were synthesized by a self-ignited sol-gel process. An annealing temperature of 950 °C is estimated via thermal-gravimetric (TGA) analysis. X-ray diffraction (XRD) scans have confirmed the formation of the ferrite phase with a spinel structure in all samples. Substitution of Ho ions on the B-site significantly reduced the porosity from 38 -to 23% and the crystallite size from 23.4 -to 21.7 nm. Microstructural analysis revealed a denser structure with an increase in Ho content. Dielectric results showed that both the dielectric loss and dielectric constant depict a nonlinear variation with the addition of Ho. Complex impedance behavior with a single semicircle for all samples suggests the predominant effect of the grain boundary mechanism. The substitution of Ho ions in place of Fe ions significantly decreased the electrical conductivity. The anisotropic Ho3+ ions reinforce the L-S coupling which consequently enhanced the coercive force from 145 -to 389 Oe, and thus the anisotropy constant. [ABSTRACT FROM AUTHOR]

Cobalt and nickel substituted BaMg2Fe16O27 W-type hexaferrite nanoparticles were synthesized via citric acid-assisted sol–gel auto-combustion technique. XRD results revealed the single-phase W-type hexagonal structure of these nanomaterials. The decrease in lattice parameters and unit cell volume is accredited to smaller ionic radii of substituted ions as compared to that of host ions. The variations in Raman spectra as a function of substitution content (x, y) are ascribed to the induction of strain in the unit cell. The PL spectra of synthesized samples revealed all emissions invisible (red) regions with PL intensity near 661 nm. Furthermore, the semiconducting nature of synthesized materials has been assessed based on bandgap energy Eg = 1.875 eV. FTIR investigations endorsed the successful settlement of substituents at tetrahedral and octahedral sites. SEM images exhibit non-homogenous hexagonal platelet-shaped particles. The research outcomes suggest the promising applications of synthesized compounds with suitable cationic substitution for microwave devices. [ABSTRACT FROM AUTHOR]

Indium (In) substituted copper ferrites with nominal composition CuIn x Fe 2-x O 4 (where 0.00 ≤ x ≤ 0.32) were prepared via sol gel route. Influence of In3+ on thermal, structural, spectral, magnetic and dielectric properties are elucidated. The complete decomposition and stable phase formation was assessed from thermal gravimetric analysis (TGA) and differential thermal gravimetric analysis (DTA). The structure of copper ferrite is single phase estimated from X-ray diffraction (XRD) analysis. Lattice constant (a) and crystallite size first increased then decreased with the inclusion of In3+ ions. Cell volume, X-ray density and bulk density are improved due to substitution of indium ions. Magnetic studies are carried out by vibrating sample magnetometer (VSM). The various magnetic parameters i.e saturation magnetization (M s), coercivity (H c) and retentivity (M R) are elucidated. The value of M s and H c are reduced with the substitution of In3+ ions. The squareness ratio, anisotropy constant and Bohr's magneton were also decreased as the inclusion of indium concentration. The value of dielectric constant (ε′), dielectric loss (ε") and tan loss were reduced as frequency increased. The surface morphology was studied by SEM (scanning electron microscopy). The small value of dielectric parameters and coercivity of synthesized ferrites suggested that indium substituted copper ferrites might be useful in switching and high frequency applications. [ABSTRACT FROM AUTHOR]

Gallium was substituted in Bi0.97K0.9Fe1−xGaxO3 (x = 0.00, 0.04, 0.08, 0.12, and 0.16) and synthesized using a simple citrate sol–gel technique. Structural, magnetic, dielectric, and optical properties were investigated. XRD patterns revealed two intense peaks (110) and (104) merged into a single peak for x = 0.08 and induced structural phase from rhombohedral to orthorhombic symmetry. Cell volume was decreased with the substitution of K-Ga up to x = 0.12. The crystallite size lies in the range of 17.90–45.71 nm. Bulk density was reduced from 2.36 to 2.24 g/cm3 because bigger ionic incorporation resulted in less diffusion at grain boundaries, increasing inner pores. The optical analysis confirmed that the Ga-O bond length was more significant than the Fe–O bond length, and the Fe–O bond length was stretched with Ga incorporation in BKFO. For x = 0.12, dielectric constant and dielectric loss decreased due to the Ga3+ ion's stable ion yield reduction of Fe3+ at octahedral sites. So, the hopping of electrons between Fe3+ and Fe2+ becomes tricky, and electron accumulation occurs at the interface of grain boundaries which hampers and decreases dielectric polarization. These results suggested that synthesized materials may be applicable in dielectric resonators, magnetic field sensors, and magnetoelectric coupling. [ABSTRACT FROM AUTHOR]

Sr 2 Ni 2 T x Fe 28-x O 46 (T = Cr3+, Bi3+, Al3+, In3+; x = 0.25) hexa-ferrites were fabricated via the sol-gel route. The phase temperature, which was obtained using thermo-gravimetric analysis (TGA), reveals that the X-type hexagonal phase of these materials is highly stable above 1200 °C. The phase formation was confirmed using X-ray diffraction (XRD) patterns. The variation in lattice strain shows the significant effect of substituted cations on the structure of the materials. The crystallite size of these materials was found in the range of 18–19 nm. The increase in dielectric constant, as well as with moderate loss, was observed in all substituted samples between 0.001 GHz and 1 GHz. The large values of dielectric constant were observed for Al3+ and In3+ substituted materials at higher frequency. The values of slope (n) reveal that all the materials exhibit frequency dependent ac conductivity. The Cole-Cole plots show the single semicircle for all samples. These semicircles of the Cole-Cole plots indicate that resistance inside the material is due to grains and grain boundaries. The both grain and grain boundaries resistance inside the material may cause large values of dielectric constant as well as the losses in the material. The large values of dielectric constant and impedance with moderate dielectric losses of these materials reflect their significant role in the fabrication of electronic devices as a radiation/microwave absorber or high frequency equipment components. Magnetic analysis shows the large values of magnetization and coercivity for Al3+ and In3+ substituted samples, which reflect that these materials might be beneficial for the absorption of electromagnetic radiation, formation of multilayer chip inductors and recording/storage purpose. [ABSTRACT FROM AUTHOR]

In the present study, the impact of holmium (Ho) substitution on structural, spectral, dielectric and magnetic behavior of Li 1.2 Zn 0.4 Ho x Fe 2−x O 4 (0.00 ≤ x ≤ 0.15) ferrites was investigated. The development of spinel phase and structural changes induced by Ho doping were confirmed by X-ray diffraction. The accommodation of Ho ions into spinel lattice was restricted for x ≥ 0.06 as indicated by ortho phase (HoFeO 3 ) traces. The decrease in lattice parameter ( a ) was attributed to the segregation of Ho ions on grain boundaries. FTIR spectra featured two intrinsic vibrational bands v 1 (617 cm −1 ) and v 2 (488 cm −1 ) for x = 0 due to tetrahedral and octahedral vibrations respectively. The compositional dependence of force constants and bond lengths has explained on the basis of cations distribution and oxygen-cation bond distances of respective sites. The addition of Ho ions decreased the saturation magnetization and optimized the coercivity from 59 to 335 Oe, proposing these ferrites for magnetic recording media. Dielectric results for the entire range of frequency (1 MHz to 3 GHz) revealed that ac conductivity increased from 3.5 × 10 5 to 1.8 × 10 6 (Ω-cm) −1 up to x = 0.09 and then it decreased slightly for x = 0.12. The effective contribution of grain-interior mechanism to dielectric behavior was confirmed by complex impedance study. The results of dielectric studies displayed that Ho doped lithium ferrites are suitable low loss potential materials for high frequency based applications. [ABSTRACT FROM AUTHOR]

Abstract A series of BiFe 1-x Hf (3/4)x O 3 (0%, 5%, 10%, 15% and 20%) nanoparticles were synthesized by simple auto combustion technique using citric acid as a fuel. Thermogravimetric (TGA), differential thermogravimetric (DTA), structural, magnetic, dielectric and ferroelectric analyses were investigated. Thermogravimetric analysis provides information of temperature at which phase develops (600 °C). DTA predicts ferroelectric to paraelectric transformation temperature which is found to be 822 °C. X-ray diffraction (XRD) results confirm formation of distorted rhombohedral structure for all compositions along with few traces of Bi 25 FeO 40. The tolerance factor is increased from 0.845 to 0.853 due to larger ionic radius of Hf4+ substitution on Fe site. Crystallite size (D) is found in the range of 24.2–30.48 nm. Saturation magnetization (Ms) is increased to 16 times and remanent magnetization (Mr) is increased to 8 times than that of pure BiFeO 3. This increment in magnetic parameters is due to reduction of oxygen vacancies, small crystalline size (less than 62 nm), structural distortion and unbalancing condition for antiferromagnetic magnetic moments of Fe3+ ions. Dielectric parameters depict decrement behavior with increasing of applied field up to 3 GHz. For Fe 1-x Hf (3/4)x O 3 , lower value of dielectric permittivity for all compositions is due to reduction of polarization and less growth of grains but more growth of grain boundaries because of mismatching of Hf and Fe3+ ions. P-E hysteresis loop changes from round shape to elliptical shape and it confirms less lossy nature of ferroelectric loops. Higher values of Ms as well as Mr but lower values of dielectric constant as well as remanent polarization for these nanoparticles make them useful for MeRAM (magnetoelectric random access memory) and high resonant applications. [ABSTRACT FROM AUTHOR]

Structural, optical, dielectric, and magnetic characteristics of Sr–Ni–W hexaferrites were probed to justify their potential use in various applications. Sr 1-x Co x Zn y Ni 2-y Fe 16 O 27 (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. [ABSTRACT FROM AUTHOR]

In this research, SnO 2 @SWCNTs@Reduced Graphene Oxide based nanocomposite was synthesized by a one step hydrothermal method and reported new cost effective platinum-free counter-electrodes (CEs) in dye-sensitized solar cells (DSSCs). The CEs were formed by using the nanocomposites with the help of a pipette using a doctor-blade technique. The efficiency of this nanocomposite revealed significant elctrocatalytic properties upon falling the triiodide, possessing to synergistic effect of SnO 2 nano particles and improved conductivity when SWCNTs dispersed on graphene sheet. Therefore, the power conversion efficiency (PCE) of prepared SnO 2 @SWCNTs@RGO nanocomposite CE attained of (6.1%) in DSSCs which is equivalent to the value (6.2%) which attained to the value (6.2%) with pure Pt CE as a reference. SnO 2 @SWCNTs@RGO nanocomposite CEs give more stable catalytic activities for triiodide reduction than SnO 2 and SWCNTs CEs in the cyclic voltammetry (CV) analysis. Furthermore, to the subsistence of graphene oxide, the nanocomposite acquired both higher stability and efficiency in the nanocomposite. [ABSTRACT FROM AUTHOR]

Ba 2−x Cu x Co 2 Cr y Fe 28−y O 46 (x = 0.0, 0.1, 0.2, 0.3, 0.4, y = 0.0, 0.2, 0.4, 0.6, 0.8) X-type hexagonal ferrites were synthesized via micro-emulsion route. The techniques which were applied to characterize the prepared samples are as follows: X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Dielectric measurements and vibrating sample magnetometer (VSM). The structural parameters i.e. lattice constant (a, c), cell volume (V), X-ray density, bulk density and crystallite size of all the prepared samples were obtained using XRD analysis. The lattice parameters ‘a’ and ‘c’ increase from 5.875 Å to 5.934 Å and 83.367 Å to 83.990 Å respectively. The crystallite size of investigated samples lies in the range of 28–32 nm. The magnetic properties of all samples have been calculated by vibrating sample magnetometer (VSM) analysis. The increase in coercivity (H c ) was observed with the increase of doping contents. It was observed that the coercivity (H c ) of all prepared samples is inversely related to the crystalline size which reflects that all materials are super-paramagnetic. The dielectric parameters i.e. dielectric constant, dielectric loss, tangent loss etc were obtained in the frequency range of 1 MHz–3 GHz and followed the Maxwell-Wagner’s model. The significant variation the dielectric parameters are observed with increasing frequency. The maximum Q value is obtained at ∼2 GHz due to which these materials are used for high frequency multilayer chip inductors. [ABSTRACT FROM AUTHOR]

Ytterbium (Yb) doped NiCr 0.1 Yb x Fe 1.9−x O 4 (x = 0.00, 0.002, 0.04, 0.06, 0.08) spinel ferrites with different crystallite sizes have been prepared by co-precipitation technique and their magnetic and dielectric properties were investigated. X-ray diffraction data suggested that, after doping, all the samples possess a main spinel phase along with few traces of YbFeO 3 (secondary phase). The addition of Yb 3+ resulted in a decrease of crystallite size and an increase in X-ray density. The magnetic measurements indicated that saturation magnetization (M s ), coercivity (H c ) and remanence (M r ) of all the samples decreased by increasing dopant (Yb) concentration. Dielectric constant, dielectric loss and tan loss were also minimized with the increase in frequency as well as increase in the concentration of Yb 3+ ions in the nickel chromium based spinel ferrites. AC conductivity was directly proportional to frequency and inversely proportional to concentration of Yb 3+ ions. These ytterbium doped nickel ferrites may be potential candidates for the fabrication and development of high frequency switching devices. [ABSTRACT FROM AUTHOR]

The influence of neodymium and nickel substitution on structural and dielectric parameters was investigated in strontium-barium X-type hexagonal ferrites having composition SrBaCu 2−x Ni x Nd y Fe 28−y O 46 (x = 0, 0.2, 0.4, 0.6, 0.8, 1 and y = 0, 0.02, 0.04, 0.06, 0.08, 0.1). Sol-gel method was employed for synthesizing these hexagonal ferrites. The XRD plots of all studied materials which were annealed at 1250 °C show single phase characteristics. Lattice parameter ‘c’ increased as a consequence of larger radius of rare earth ion (Nd 3+ ) as compared to (Fe 3+ ), while lattice parameter ‘a’ showed very small variation. The cell volume was obtained in the range 2508.32–2523.75 (Å 3 ). The inclusion of Nd-Ni also affected X-ray density, bulk density and porosity. The FTIR spectroscopy indicated the particular absorption peaks of hexagonal ferrites and it was performed in the range of 500–700 cm −1 . On account of Nd-Ni doping, the dielectric constant, dielectric loss and AC-conductivity showed decreasing trend. The occupancy of Nd 3+ ions at octahedral site impedes the valence alternation of Fe 3+ ; therefore there was decrease in dielectric permittivity. Ac conductivity has been decreased from 9.14 to 6.49 (Ω cm) −1 at frequency of 2.7 GHz. The Cole-Cole plots of synthesized materials noticeably revealed grain boundary contribution. The appearance of single semi-circle in impedance Cole-Cole graphs confirms the exceptional role of grain boundaries in the conduction process. The considerably lower dielectric parameters of investigated nano X-type ferrites propose their feasibility for high-frequency applications (phase shifters, dielectric resonators, stealth technology etc). [ABSTRACT FROM AUTHOR]

Neodymium-nickel (Nd-Ni) substituted nanocrystalline ferrites of the following chemical formula SrBaCu 2−x Ni x Nd y Fe 12−y O 22 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, y = 0.0, 0.02, 0.04, 0.06, 0.08, 0.1) were synthesized by the sol-gel auto-combustion route. The synthesized samples were characterized by X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR) and dielectric measurement techniques. The properties related to structure of the prepared samples were examined in detail in addition to thorough analysis of their dielectric properties. Microstructural studies exposed the formation of spherical, elongated grains and all the prepared samples showed single Y-type hexagonal phase and lattice parameters have been calculated. FTIR technique was employed to explore the local symmetry behavior in the synthesized crystalline materials and to probe the process of ordering in nano-crystalline ferrites. With increase in frequency and Nd-Ni contents, dielectric constant and dielectric loss of the samples was found to decrease. The complex impedance formalism confirms the role of grain-interior phenomenon to the dielectric properties. Resistive and capacitive characteristics of materials were exhibited by Cole-Cole plots having single semicircle, caused by contribution of grain boundaries in prepared Y-type nano materials. [ABSTRACT FROM AUTHOR]

CoTb 0.03 Fe 1.97 O 4 ferrite and poypyrrole (PPy) polymer nano composites were prepared by mixing the nano crystalline ferrite with poypyrrole (PPy) by following the solid state reaction synthesis route. The XRD patterns of CoTb 0.03 Fe 1.97 O 4 spinel ferrite powders and polymer (PPy) exhibited single phase spinel structure. The amorphous nature of PPy was evidenced by the broad peaks of XRD patterns. The surface morphology unfolded heterogeneous distribution in composites and ferrite. The grains in ferrite were spherical in shape with clear boundaries. The morphology was appreciably altered by the inclusion of ferrite contents. The higher activation energy and resistivity aroused due to blocking of conduction mechanism owing to nanoparticles embedded in the PPy matrix. A downfall in the dielectric loss of the composites is observed as the frequency of the applied field is increased. The incorporation of ferrite contents optimized the magnetic parameters of the composites. The enhanced coercivity (Hc) of these nanocomposites might be beneficial for memory devices. [ABSTRACT FROM AUTHOR]

Ytterbium (Yb) doped X-type hexagonal nano-sized ferrites (Sr 2 NiCoFe 28 O 46 ) were fabricated by micro-emulsion method. The development of hexagonal structure of ferrite materials was confirmed by XRD analysis. The size of crystallites as determined by Scherrer's formula was found in the range 29–41 nm. The lattice strain of these ferrites was increased from 3.62 × 10 −2 to 3.73 × 10 −2 with the increased Yb-contents. The tetrahedral absorption bands shifted slightly towards higher frequency whereas octahedral bands shifted towards lower frequency side. The incorporation of Yb enhanced dc electrical resistivity significantly from 2.05 × 10 8 to 3.35 × 10 9 Ω-cm. The AC conductivity was increased with frequency whereas it decreased with the inclusion of Yb 3+ ions. This distinctive behavior of these hexagonal ferrites may be suitable for microwave devices and electromagnetic attenuation applications. The doping of Yb 3+ optimized coercivity whereas remanence and saturation magnetization were decreased. These ferrite materials can be used in longitudinal recording media due to more thermally stable and higher coercivity (577–671 Oe). [ABSTRACT FROM AUTHOR]

Nano-sized Zr-Co doped nickel ferrites with nominal composition, NiZr x Co x Fe 2-2x O 4 ( x =0.0, 0.2, 0.4, 0.6, 0.8) were synthesized using the micro-emulsion route. The structural elucidation of the synthesized materials was carried out by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The XRD analysis confirmed face centered cubic (FCC) structure of all compositions of NiZr x Co x Fe 2-2x O 4 nanocrystallites. Crystallite size was calculated by Scherrer's formula found in the range 10–15 nm. The variation in lattice parameter as determined by XRD data agreed with size variation of host (Fe 3+ ) and guest (Zr 4+ and Co 2+ ) cations. FTIR spectra of doped NiFe 2 O 4 exhibited the typical octahedral bands at 528.4 cm −1 which is the characteristic feature of spinel structure of spinel ferrites. The characterized spinel NiZr x Co x Fe 2-2x O 4 nano-ferrites were evaluated for their potential applications by magnetic hysteresis loops and dielectric measurements. The value of saturation magnetization ( M s ) decreased from 47.9 to 13.09 emu/g up to x =0.8 with ups and downs fluctuations in between x=0.0 to x=0.8. The high values of Ms of some compositions predicted the potential applications in high density perpendicular recording media and microwave devices. The frequency dependent behavior of permittivity (ε') is recorded and discussed with the help of hopping mechanism of both holes and electrons. The dielectric and magnetic data of NiZr x Co x Fe 2-2x O 4 nano-ferrites suggested the potential applications of these ferrite nanoparticles in high frequency and magnetic data storage devices fabrication. [ABSTRACT FROM AUTHOR]

A series of Dy-doped Li–Ni ferrites of the following composition Li 0.5 Ni 0.48 Tb 0.02 Dy x Fe 2−x O 4 (0.2≤x≥0) was synthesized by the microemulsion method. The X-ray diffraction (XRD) analysis indicated that Li 0.5 Ni 0.48 Tb 0.02 Dy x Fe 2−x O 4 nano-crystalline ferrites exhibited the single-phase spinel structure. The lattice parameter was determined by the Nelson-Riley refinement technique and it increased by increasing the Dy contents. The crystallite size was computed from the Debye Scherrer's formula and it was in range from 27 to 40 nm. The thermal decomposition process was studied by the thermogravimetric analysis and the annealing temperature observed was 980 °C. The real and complex parts of dielectric constant decreases very sharply in the lower frequency region, but in the higher frequency region, the real and complex part of dielectric constant show variable values with Dy contents. The dielectric tangent loss (tan δ) decreases exponentially with Dy contents. The magnitude of the ac conductivity decreases in certain frequency region, as the Dy contents are increased. The possible mechanisms contributing to the above behavior are discussed. The results of these nanocrystalline ferrites are very suitable materials for microwave device applications. [ABSTRACT FROM AUTHOR]

New X-type hexagonal Yb 3+ -doped Ba 2 Co 2 Fe 28 O 46 ferrites were prepared via wet chemical route. The Yb 3+ -contents in Ba 2 Co 2 Yb x Fe 28−x O 46 were kept from 0.00 mol to 0.15 mol in six different compositions. XRD patterns in two theta range 15–70 confirmed the X-type hexagonal ferrites with crystallite size <40 nm. Predicted appropriate variations in lattice parameters and cell volume confirmed the successful substitution of Fe 3+ ions with Yb +3 ions at octahedral sites. The bulk density (D b ), X-ray density (D x ) and porosity (P) were also significantly varied by increased Yb 3+ contents. The fourier transform infrared (FTIR) spectra exhibited the metal-oxygen (Fe-O) stretching vibrational band which further confirmed the successful preparation of hexagonal ferrites. The FTIR band at wave number 1029 cm −1 indicated the presence of cobalt in the pure and un-doped sample which is the characteristic feature of cobalt ferrite. The magnetic measurements carried out in the range −10000 to 10,000 oersted (Oe) at room temperature indicated the increased coercivity (H c ) from 236.4 to 532.7 Oe by increased Yb 3+ contents. However the saturation magnetization (M s ) was decreased from 27.4 to 8.6 emu/g) and retentivity (M r ) decreased from 5.2 to 3 emu/g. The decreased Ms and Mr values are attributed to the modified cationic distribution and re-distribution of cations. The squareness values < 0.5 suggested the multi-magnetic domain structure. The dielectric parameters i.e. dielectric constant, dielectric loss and tangent loss were measured in the frequency range of 1 × 10 6 to 3 × 10 9 Hz and these parameters showed appropriable variations in high frequency region. The optimized dielectric parameters suggested that these prepared hexagonal ferrites can be used in the fabrication of multilayer chip inductors (MLCI's) circuits. [ABSTRACT FROM AUTHOR]

Gadolinium (Gd) and Dysprosium (Dy) co-doped Ni-Co (Ni 0.4 Co 0.6 Fe 2 O 4 ) ferrites were prepared by micro-emulsion route. X-ray diffraction (XRD) analysis indicated the development of cubic spinel structure. The lattice parameter and X-ray density were found to increase from 8.24 to 8.31 Å and 5.57 to 5.91 (gm/cm 3 ) respectively as the Gd-Dy contents increased in nickel-cobalt ferrites. The crystallite size calculated from the Scherrer's formula exhibited the formation of nanocrystalline ferrites (13–26 nm). Two foremost absorption bands observed in FTIR spectra within 400 cm −1 (υ 2 ) to 600 cm −1 (υ 1 ) which correspond to stretching vibrations of tetrahedral and octahedral complexes respectively. The dielectric constant (ε) and dielectric loss (tanδ) were decreased by the optimization of frequency and abrupt decrease in the low frequency region and higher values in the high frequency region were observed. The dielectric dispersion was due to rapid decrease of dielectric constant in the low frequency region. This variation of dielectric dispersion was explicated in the light of space charge polarization model of Maxwell-Wagner. The dielectric loss occurs in these ferrites due to electron hopping and defects in the dipoles. The electron hopping was possible at low frequency range but at higher frequency the dielectric loss was decreased with the decrease of electron hopping. Magnetic properties were observed by measuring M-H loops. Due to low dielectric loss and dielectric constant these materials were appropriate in the fabrication of switching and memory storage devices. [ABSTRACT FROM AUTHOR]

Terbium (Tb) and dysprosium (Dy) doped lithium-nickel nano-sized ferrites (Li 0.2 Ni 0.8 Tb 0.5 x Dy 0.5 x Fe 2− x O 4 where x =0.00−0.08) were prepared by micro-emulsion technique. The X-ray diffraction (XRD) patterns confirmed the single phase cubic spinel structure. The lattice constant was increased due to larger ionic radii of Tb 3+ and Dy 3+ cations. The crystallite size was found in the range 30–42 nm. The FTIR (Fourier transform infrared spectroscopy) spectra revealed two significant absorption bands (~400–600 cm −1 ) which indicate the formation of cubic spinel structure. The peaking behavior of dielectric parameters was observed beyond 1.5 GHz. The dielectric constant and dielectric loss were found to decrease by the increase of Tb–Dy contents and frequency. The doping of Tb and Dy in Li–Ni ferrites led to increase the coercive field (120–156 Oe). The smaller magnetic and dielectric parameters suggested the possible utility of these nano-materials in switching and microwave devices applications. [ABSTRACT FROM AUTHOR]

A series of holmium (Ho) doped nanocrystalline Ni 0.7 Zn 0.3 Ho 2x Fe 2–2x O 4 ; 0.0≤x≤0.07 ferrite was synthesized using the conventional ceramic technique. The cubic spinel structure was confirmed by powder X-ray diffraction (XRD). The lattice parameter increases with increase in Ho content due to large ionic radius of Ho 3+ (0.901 Å) as compared to Fe 3+ (0.67 Å). Room temperature DC electrical resistivity and activation energy both increase with the increase of holmium contents. The saturation magnetization (M s ) decreased gradually from 78.92 to 54.17 emu/g due to holmium ions substitution in Ni-Zn ferrites. This decrease in M s is explained on the basis of redistribution of cations amongst the sites and weakening the A-B exchange interactions. An increase in electrical resistivity made this material suitable for its use in high frequency device applications. [ABSTRACT FROM AUTHOR]

The substitution of Neodymium (Nd) in the cobalt - zinc (Co–Zn) ferrite was analyzed. The sol-gel technique was used to synthesize the se ceramic samples. The crystalline structural, molecular characterizations, and magnetic properties were analyzed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) experiments, and vibrating sample magnetometer (VSM) respectively. XRD patterns revealed the single-phase cubic spinel structure of the samples. Lattice p arameter varied from 8.41 to 8.38 Å with the inclusion of Nd concentration. The existence of two characteristic frequency bands in the range of 400–1400 cm−1 was confirmed by FTIR spectra. VSM measurements showed the magnetic behaviour at room temperature. The saturation magnetization was noted to decrease from 81 to 66 emu/g with increasing the Nd concentration. The sample having step size x = 0.025 revealed the highest coercivity and retentivity. Dielectric properties were studied and showed variation in dielectric constant, dielectric loss, ac conductivity, and energy dissipation (tangent loss) in the prepared material s. • Auto-citric combustion method was used to prepare Co0·6Zn0.4NdxFe2-xO4 ferrites. • The estimated value of constant lattice decreases upon increasing Nd ions. • Intrinsic vibrational bands revealed a shift with increasing the Nd content. • The porosity of the samples increased from 0.41 to 0.55. • Nd inclusion optimized saturation magnetization and coercivity. [ABSTRACT FROM AUTHOR]

Rare-earth (RE=La 3+ , Nd 3+ , Gd 3+ , Tb 3+ , Dy 3+ ) doped Ba 2 NiCoRE x Fe 28− x O 46 ( x =0.25) hexagonal ferrites were synthesized for the first time via micro-emulsion route, which is a fast chemistry route for obtaining nano-sized ferrite powders. These nanomaterials were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), as well as vibrating sample magnetometer (VSM). The XRD analysis exhibited that all the samples crystallized into single X-type hexagonal phase. The crystalline size calculated by Scherrer's formula was found in the range 7–19 nm. The variations in lattice parameters elucidated the incorporation of rare-earth cations in these nanomaterials. FTIR absorption spectra of these X-type ferrites were investigated in the wave number range 500–2400 cm −1. Each spectrum exhibited absorption bands in the low wave number range, thereby confirming the X-type hexagonal structure. The enhancement in the coercivity was observed with the doping of rare-earth cations. The saturation magnetization was lowered owing to the redistribution of rare-earth cations on the octahedral site (3b VI ). The higher values of coercivity (664–926 Oe) of these nanomaterials suggest their use in longitudinal recording media. [ABSTRACT FROM AUTHOR]

BiFe 1–2x Zr x Mg x O 3 (x = 0.00, 0.05, 0.1, 0.15, 0.2 and 0.25) nano-sized multiferroics were synthesized by micro emulsion technique. The structure analysis, thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FTIR), magnetic measurements and dielectric properties were studied for prepared samples. Differential scanning calorimetry (DSC) and differential thermogravimetric analysis (DTA) confirm multiferroic characteristics of the samples. DTA curve indicates the presence of ferroelectric transition temperature at 806.79 °C. XRD results indicated that crystallite size is found in the range of (22.5–18.00) nm and other parameters like bulk density, X-ray density and porosity were also measured from the XRD data and were greatly influenced by increasing the dopants concentration. FTIR spectra revealed that the characteristics bonds of BiFeO 3 are appreciably influenced by Zr–Mg contents. Magnetic analysis reveals that saturation magnetization (Ms) and remanent (Mr) increase with Zr–Mg doping because magnetic moment of Zr 4+ is zero and doping of Zr 4+ at Fe 3+ site increase align spin but Mg 2+ doping in BiFeO 3 increases saturation magnetization not too much as compared to other alkaline earth metal ions because Mg 2+ contain smallest ionic radius among alkaline earth metals. Ms reaches maximum value of 0.979 emu/g for composition x = 0.25. Multiferroics BiFe 1–2x Zr x Mg x O 3 are useful for ferroelectric random access memories (FeRAM) where data can be written electrically and read magnetically. It is found that all dielectric parameters strongly dependent on Zr–Mg contents. At higher concentrations, complicated dielectric behavior is observed. Dielectric results exhibited that dielectric parameters decrease with increase in frequency in the range of 1 MHz–3 GHz suggest that these multiferroics are useful for high resonant circuits. [ABSTRACT FROM AUTHOR]

Terbium (Tb) doped X-type hexagonal nano-ferrites Sr 2 NiCoTb x Fe 28− x O 46 ( x =0.00, 0.05, 0.1, 0.15, 0.2) were synthesized via micro-emulsion route. Single phase X-type hexagonal structure was confirmed by X-ray diffraction (XRD) analysis. The crystallite size of the samples was found in the range of 15–25 nm. The bulk density and X-ray density were enhanced while porosity was reduced with the increased Tb 3+ contents. The development of hexagonal phase was investigated by thermogravimetric analysis. The fourier-transform infrared (FTIR) spectra revealed the formation of spectral bands (metal-oxygen stretching vibration) which confirmed the hexagonal ferrites. The dielectric constant has high value at low frequency and decreased with increased frequency. The dielectric loss is appreciably decreased by the Tb 3+ incorporation and resonance phenomenon occurred beyond 1.7×10 9 Hz. The saturation magnetization (76–54 emu/g) and remanance (27–21 emu/g) decreased while coercivity increased (610–747 Oe) by Tb 3+ -incorporation in Sr 2 NiCoTb x Fe 28− x O 46 ferrite. The values of squareness ratio (0.35–0.39) indicated that Tb-doped samples are single domain while un-doped material is multi domains. These synthesized nano-sized hexagonal ferrites have potential applications in high frequency and recording media devices. [ABSTRACT FROM AUTHOR]

In this study, novel three-phase hybrid (inorganic-organic) composite comprising Fe0.01La0.01Al0.5Zn0.98O ceramic particles (FLAZPs), conducting polymer polyaniline (PANI) and grapheme oxide (GO) was synthesized. The ceramic particles were produced by sol-gel technique. For the homogeneous dispersion of FLAZPs particles in the PANI matrix, in-situ free-radical polymerization of aniline (PANI precursor) was performed. FLAZPs distributed in the matrix during the polymerization process. GO was synthesized via modified Hummer's method which was then blended with two-phase composite using simple one-pot blending technique. The prepared materials were subjected to FT-IR, TGA, XRD and SEM to analyze their physical properties. FT-IR showed the successful complexation of the materials with one another. XRD confirmed the crystalline nature and phase distribution in the composites. FLAZPs enhanced the thermal stability of PANI and GO in the composites. SEM showed that ceramic particles are in the range from micro to nanometer and are well dispersed in the PANI matrix in two-phase composite. Furthermore, GO prevented the agglomeration of particles while interacting with PANI in the three-phase composite. Extensive dielectric studies were carried out which showed that PANI and GO have about the same additional effect on various dielectric properties of FLAZPs. The AC conductivity (σ = 7.79 x 10-1 Ω-1cm-1) achieved by two-phase and three-phase composites is much higher in comparison to pure FLAZPs (σ = 3.17 x 10-1 Ω-1cm-1). [ABSTRACT FROM AUTHOR]

Novel Ni 0.6 Zn 0.4 Y 2 x Fe 2−2 x O 4 soft spinel ferrites were prepared via double sintering ceramic route. The influence of Y 3+ cations on structural, morphological, electrical and dielectric properties was investigated. X-ray diffraction (XRD) confirmed the formation of single phase spinel structure for 0≤ x ≤0.06 and thereafter a small peak of orthorhombic phase (FeYO 3 ) appeared for x >0.06. The incorporation of yttrium altered the lattice constant. The variation in lattice constant with respect to the Y 3+ contents was non-linear. The variation of lattice constant may be attributed to larger ionic radius of Y 3+ as compare to Fe 3+ cations and solubility limit of substituted cations. Fourier transform infrared (FTIR) spectra showed two strong absorption bands around 600 cm −1 and 400 cm −1 which confirmed the spinel structure. The dc electrical resistivity was found to increase from 5.67×10 5 to 8.48×10 8 Ω cm with the increased Y 3+ contents. The dielectric constant and dielectric loss tangent were significantly impeded by increasing the yttrium contents. The optimized electrical resistivity and reduced dielectric parameters suggest the possible use of these ferrites in the fabrication of microwave devices. [ABSTRACT FROM AUTHOR]

Co and Ni substituted znic ferrite nanoparticles (Zn 1− x Co 0.5 x Ni 0.5 x Fe 2 O 4 ) (0.00≤ x ≥0.75) were synthesized by co-precipitation method. X-ray diffraction and Fourier transform infrared spectroscopy confirmed the single phase spinel structure. The lattice constant decreased with the increased Co and Ni contents. The bulk density was found less as compared to the X-ray density and this difference was explained in terms of porosity. The crystallite size was calculated by Scherrer's formula and found in the range 20–50 nm. Two prominent stretching bands were observed in FTIR spectra around 400–600 cm −1 . These two bands confirmed the spinel structure of the prepared nanoparticles. The saturation magnetization was found to increase upto x =0.60 from 1.31 emu/g to 81.2 emu/g then it decreased for x =0.75 to the value of 75.1 emu/g. The coercivity and retentivity were found in the range 35.36–226.125 Oe and 0.0135–19.8 emu/g, respectively. Dielectric parameters were decreased with the increased Ni–Co contents. About nine fold increase in the DC-electrical resistivity was obtained for the Zn 0.25 Co 0.375 Ni 0.375 Fe 2 O 4 (2.8979×10 10 Ω cm) as compared to the ZnFe 2 O 4 (0.2974×10 10 Ω cm) nanoparticles. [ABSTRACT FROM AUTHOR]

Co-precipitation method was used to synthesize the nanoparticles of cobalt substituted zinc–magnesium ferrites having formula “Mg 0.6−0.5 x Zn 0.4−0.5 x Co x Fe 2 O 4 ” where 0.00 ≤ x ≤ 0.25 . Fabricated samples were annealed at 750 °C for 6 h. The cubic spinel structure of Mg 0.6−0.5 x Zn 0.4−0.5 x Co x Fe 2 O 4 nanocrystals was confirmed by Fourier transformed infra-red (FTIR) and X-ray diffraction (XRD). Lattice parameter, crystalline size, cell volume, X-ray density, bulk density and porosity were also determined using XRD data. Lattice parameter exhibits overall decreasing trend (0.824–0.817 nm) with cobalt content; it is due to the substitution of cobalt (having smaller ionic radii) with magnesium and zinc ions. Cation distribution among A and B sites were studied by FTIR spectrum. Vibrating sample magnetometery (VSM) was used to investigate magnetic properties of as prepared nanoparticles. Coercivity exhibits the inverse relation to crystalline size. Lowest value of coercivity (47.722 Oe) was obtained for the sample having x =0.15. Dielectric constant, dielectric loss and dielectric tan loss were inversely related with the frequency. [ABSTRACT FROM AUTHOR]

In this manuscript, we have grown the AgMoO 3 thin film by a simple thermal evaporated method. To attain the best quality film, post-annealing the grown thin films for different temperatures (450 K, 500 K, and 550 K) was performed. The XRD data shows the formation of AgMoO 3 thin film and different secondary phases. The SEM data have shown the small spherical grains on the thin film surface, which confirm the creation of extra secondary phases and the cracks on the film with post-annealing due to intrinsic stress. The absorption coefficient and energy bandgap have also increased with the post-annealing temperature. The Seebeck data indicated an enhancement in Seebeck coefficient value from 237 to 410 μV/K as the as-grown to post-annealed samples. The electrical conductivity measurements also showed an increasing trend. The Seebeck coefficient and electrical conductivity enhancement were increased by creating a different secondary phase that caused the carrier localization. Improved mobility of carriers due to the change in crystal structure has resulted in an increased power factor of 1.19 × 10−3 Wm−1K−2. • Synthesized the AgMoO 3 thin film using a simple thermal evaporated method and post annealed at 450 K, 500 K, and 550 K. • The fabrication of AgMoO 3 thin film was confirmed by XRD and SEM. • The absorption coefficient and energy band-gap have also increased with the post-annealing temperature. • The power factor value of AgMoO 3 thin film was increased with rising the post-annealing temperature. [ABSTRACT FROM AUTHOR]

• Sol-gel technique was employed to synthesize Ba 4 Cu 2-x Ni x Fe 36 O 60 ferrites. • Cole-Cole plots markedly distinguished grain boundary contribution. • Coercivity (H c) increased (1844.44–2946.83 Oe) by increasing Ni contents. • The squareness ratio (0.471–0.450) revealed single magnetic domain. • The results suggest their potential use in high-frequency applications. This paper reports the impacts of nickel substitution on dielectric, magnetic, and structural characteristics of Ba 4 Cu 2-x Ni x Fe 36 O 60 hexaferrites prepared via the sol–gel method. The sample was annealed for 5 h at 1200 °C. The crystalline structure, magnetic and dielectric features were examined by X-ray diffraction, vibrating sample magnetometer, and impedance analyzer individually. The specific absorption bands of hexagonal ferrites were identified by FTIR spectroscopy and in the 420–600 cm−1 range. M−H loops of samples were determined to examine the magnetic properties of synthesized materials. Magnetic measurement shows that samples exhibit ferrimagnetic behavior at room temperature. The magnetic properties are described in cation distribution and grain size effect. Dielectric properties of the samples were observed in the frequency range (1–3 GHz). Cole-Cole graphs of prepared materials revealed the influence of grain boundaries. A single semi-circle in the impedance Cole-Cole plots approves a special part of grain boundaries in the conduction process. Dielectric properties are affected by the electron hopping mechanism between Fe2+ and Fe3+ ions. These performances expose that these nanomaterials are appropriate for high-frequency applications. [ABSTRACT FROM AUTHOR]

Polycrystalline ferrites with chemical formula MgY 2 x Fe 2−2 x O 4 ( x =0.0 to 0.12) have been fabricated by a double sintering ceramic technique. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Impedance spectroscopy and Fourier transform infrared (FTIR) spectroscopy. A slight increase in lattice constant is observed for x =0.02 and thereafter it decreased for higher Y-contents. The increase in lattice constant is attributed to the difference in ionic radii of the cations involved and decrease led to the formation of secondary phase (YFeO 3 ). The substitution of yttrium impedes the grain growth. The resistivity at 298 K was significantly enhanced as the Y 3+ was increased. The FTIR band positions in the range of 370–1100 cm −1 exhibited two main absorption bands. These bands confirmed the completion of solid state reaction. As the Yttrium contents were increased the dielectric parameters were greatly influenced. Both the observed/optimized electrical and dielectric parameters suggested the potential use of the Y-doped MgFe 2 O 4 ferrites in high frequency devices fabrication. [ABSTRACT FROM AUTHOR]

Nanocrystalline Mg 0.96 Tb 0.04 Fe 2 O 4 spinel ferrite was prepared by the co-precipitation technique. The polypyrrole was synthesized by in situ polymerization method. The nanocomposites were fabricated by mixing the Mg 0.96 Tb 0.04 Fe 2 O 4 ferrite nanomaterials with polypyrrole polymer. The structural, morphological and magnetic properties of nanoferrite powder and nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results of XRD revealed that the small concentrations of terbium ions are successfully incorporated into the spinel lattice. The intensity of the most intense peak increases with the increase of ferrite contents while its broadening is decreased. FTIR spectra demonstrated that there are interactions between ferrite particles and polypyrrole. SEM showed that the nanocomposites have core shell structure and inhomogeneous grain size distribution. Under the influence of applied magnetic field these nanocomposites displayed hysteresis loops which unfold the ferromagnetic behavior. The magnetic parameters such as saturation magnetization and coercivity of nanocomposites are affected by the increased concentration of ferrite particles. The magnetic parameters of nanocomposites are tailored by controlling the ferrite contents. Super paramagnetic behavior of two compositions (FP1=25% ferrite and FP2=50%) suggested that these ferrite/polymer composites may be recommended for the hyperthermia applications. [ABSTRACT FROM AUTHOR]