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Abstract: We have prepared BaCd2−x Sr x Fe16O27 (x =0, 0.5, 1, 1.5 and 2.0) W-type hexagonal ferrites by standard ceramic method. In this work, the structural, dielectric and magnetic properties have been studied of the prepared samples. The XRD analysis of the samples reveals single phase behavior sintered at 1400°C for 6h. The saturation magnetization (M s ) shows increasing behavior with the increasing concentration of Sr2+. While the coercivity (H c ) decreases rapidly up to 409G for x =1.5 and then increases for (x >1.5) due to the preference of Cd2+ for tetrahedral sites and the number of spin-down magnetic ions. The real and imaginary parts of the dielectric constant (ɛ′,ɛ″) and dielectric loss tangent (tan δ) are determined in the frequency range 0.1–107 Hz. It is observed that both the real and imaginary parts of the dielectric constant and tan δ decrease with the increasing concentration of Sr2+, which is due to the contribution of Cd2+ ions in addition to Fe3+ and Fe2+ ions to interfacial polarization. [Copyright &y& Elsevier]

Abstract: CoZn ferrite–SiO2 composites having general formula (1− x)Co0.5Zn0.5Fe2O4 + xSiO2 with x =0.0–0.8 were prepared by co-precipitation technique. The X-ray diffraction analysis of the composites reveals that they are bi-phase. Room temperature resistivity increases from 105 to 109 (Ωcm) from x =0.0–0.8. This drastic increase in resistivity may be attributed to the presence of pores and the segregation of Si at grain boundaries. The Arrhenius plots of these samples show that resistivity decreases as the temperature increases indicating their semi conducting behavior. Arrhenius plots show a change of slope at particular temperature (except for x =0.8) that may be attributed to their Curie temperature. It is observed that the activation energies are small in Para-region as compared to Ferri-region and is an indication of the hopping conduction mechanism. The variation of thermopower with temperature reveals that these samples are degenerate type semiconductors. The values of activation energies calculated from log μ d vs. 1000/T are slightly lower than the values of activation energies obtained from Arrhenius plots. This suggests that the conduction phenomenon is due to polaron hopping. [Copyright &y& Elsevier]

Abstract: A series of single phase W-type Sr3−x Ce x Fe16O27 (x=0, 0.02, 0.04, 0.06, 0.08, 0.10) hexagonal ferrites prepared by the Sol–Gel method was sintered at 1050°C for 5h. The X-ray diffraction analysis reveals that all the samples belong to the family of W-type hexagonal ferrites. The c/a ratio falls in the range of W-type hexagonal ferrites. The grain size was measured by SEM varies from 0.7684 to 0.4366μm which shows that the Ce3+ substituted samples have smaller grain size than pure ferrite Sr3Fe16O27 which results from the difference in ionic radii of Ce3+ (1.034Å) and Sr2+ (1.12Å). The room temperature resistivity of the present samples varies from 6.5×108 to 272×108 Ω-cm. The coercivity increases from 1370 to 1993Oe which is consistent with the decrease in grain size. The coercivity values indicate that the present samples fall in the range of hard ferrites. The large value of H c may be due to domain wall pinning at the grain boundaries. [Copyright &y& Elsevier]

Abstract: Nano-sized and single phase W-type hexaferrite (BaCo2Fe16O27) powders synthesized by sol–gel autocombustion method have been investigated. The samples were sintered in a temperature range of 1000–1200°C for 5h. The thermal decomposition behavior of as-prepared powder was studied by thermogravimetry (TG), differential thermal analysis (DTA) and infrared spectra (IR). The structural and magnetic properties of powders were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The grain size calculated by Scherer equation was found in the range of 36–47nm which is small enough to obtain a suitable signal-to-noise ratio in high density recording media. Hysteresis loop measurements show that the coercivity values lie in the range of 210.61–1602.6Oe with increasing sintering temperature. Magnetization studies show a significant increase in the values from 15 to 22emu/g. The dc electrical resistivity is observed to decrease up to a certain value as the temperature increases and then rises at higher temperature. [Copyright &y& Elsevier]