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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]

Abstract: Effect of Pr–Ni substitution on structural and magnetic properties of Ca0.5Ba0.5−x Pr x Ni y Fe12−y O19 (x=0.00–0.10 and y=0.00–1.00) prepared by the sol–gel auto combustion method were investigated. The XRD analysis confirmed the single phase M-type hexa-ferrite structure. The lattice parameters were found to increase as Pr–Ni content increases, which is attributed to the ionic size of the implicated cations. The Pr–Ni seems to be completely soluble in the lattice. Transmission electron microscopy reveals that the grain size decreases with increase of Pr–Ni substitution. The coercivity and remanent magnetization ranges from 1511 to 1925 (Oe) and 21.4 to 26.5 (emu/g), respectively. The coercivity values of all the samples fall in the range of M-type hexa-ferrites. [Copyright &y& Elsevier]

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]