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M -type hexagonal ferrites with compositions Ca 1 − x CrxFe 1 2 O 1 9 at (x = 0. 1 , 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 M -type hexagonal structure was revealed by X-ray diffraction (XRD) with extra 101 peak of PVA at 2 θ = 1 8 ∘ . 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 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. The formation of PVA-Ferrite Nanocomposites was confirmed by the FTIR in the range of 3500–400 cm–1 wavenumbers. The FTIR spectra of ferrite-polymer composites (PF3,PF5) were shown. The absorption bands in the range of 500–600 cm–1 wavenumbers are due to stretching vibrations at tetrahedral sites and absorption bands in the 400–500 cm–1 wavenumbers demonstrate the octahedral site formation in the M-type hexagonal ferrites structure. The absorption band at 1600 cm–1 is due to the stretching bands of hydroxyl group -O-H. Slight shifts in the bands were recorded due to the addition of polymer. Due to the interaction of ferrites-polymer, force constant and electron density were found to be decreased. [ABSTRACT FROM AUTHOR]

[Display omitted] • M type hexaferrites with composition Pb 1-x Cr x Fe 12 O 19 x = (0.0,0.1,0.2,0.3,0.4,0.5) were synthesized by the sol-gel auto combustion technique. • Peaks of the XRD pattern match well with the standard pattern of P63/mmc group with JCPDS card No (43-0002). • Crystallite size lies in the range of 63–53 nm. Lattice parameters, crystallite size and cell volume was found to decrease with the substitution of Cr3+ content. • Dielectric constant and ac conductivity (σ ac) increases gradually with the increase in Chromium doping. Mofreover, Pb 1-x Cr x Fe 12 O 19 with x = 0.2 have exceptional dielectric properties with significant Q-value (4900). • These samples may suitable for high frequency applications such as phase shifter, modulators and also in longitudinal recording media. Chromium substituted M-type hexagonal ferrites with nominal composition Pb 1-x Cr x Fe 12 O 19 where x= (0.0, 0.1, 0.2, 0.3, 0.4, 0.5) were prepared via sol gel route. Structure of the single phase lead hexaferrite was estimated from X-ray diffraction (XRD) analysis. Scanning electron microscopy (SEM) confirmed the formation of hexagonal platelets with an average grain size in the range of 53–63 nm. Crystallite size, lattice parameters and cell volume was found to decrease with the increase of Chromium concentration. Magneto crystalline anisotropy and saturation magnetization has been explored through the law of approach to the saturation magnetization. Saturation magnetization first increased and then found to be maximum (64 emu/g) at 30% of Cr3+ doped lead hexaferrite and minimum coercivity (6.54 KOe) was perceived for this composition. Dielectric constant, dielectric loss, tangent loss, real and imaginary part of electric modulus, ac conductivity and Q-values of the prepared samples were also explained. With the increase of dopant (Cr3+) concentration, dielectric constant was increased gradually. These characteristics are suitable for various applications such as phase shifter, modulators, stealth technologies and also in Multilayer chip inductor. [ABSTRACT FROM AUTHOR]

Holmium (Ho 3+ ) substituted W-type hexagonal ferrites (BaCo 2 Fe 16 O 27 ) were prepared by sol gel auto-combustion technique. The precursors were prepared by Ba 2+ , Fe 3+ nitrates solutions with citric acid as chelating agent. The prepared powder was sintered at 950 °C for 8 h to produce a single phase of W-type hexa ferrite with corresponding crystallite size ranging from 34 nm to 44 nm. The thermal decomposition of nitrate-citrate gel of as-prepared powder was investigated by TGA and DTA. The FTIR spectral study reveals the presence of two absorption bands which are characteristics of hexaferrites. DC electrical resistivity increases from 3.01×10 9 to 5.69×10 10 (ohm-cm). The real and imaginary parts of dielectric constant (ɛʹ, ϵ״) and dielectric loss tangent (tan δ) are determined in the frequency range of 20 Hz–1 MHz. It was observed that both real and imaginary parts of the dielectric constant and tanδ decrease with the increase of frequency on the basis of Wagner and Koop's theory. [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]

Highlights: [•] The decreasing trend of saturation magnetization is attributed to the weakening of exchange interactions. [•] The change in lattice constant at x >0.04 indicated the solubility limit of Gd in the spinel lattice. [•] The high coercive Li–Mg ferrites may be suitable for high frequency microwave absorption. [Copyright &y& Elsevier]