Ferrite nanoparticles, particularly nickel-zinc ferrite nanoparticles, are novel materials for high-frequency applications. Nanoparticles with a composition of Ni 0.5 Zn 0.5 Fe 2 O 4 were prepared by two different processes, namely the co-precipitation and simplified sol-gel methods. Powder x-ray diffraction (XRD) patterns confirmed the single-phase spinel structure for the as-prepared samples. Samples were sintered at 555 and 755 • C, after which the structural, electrical and magnetic properties were studied. The crystallite sizes, as determined from XRD data, increased with sintering temperature. The dc electrical resistivity measurements were performed as a function of temperature, with the two-probe method in the temperature range from room temperature to 450 • C. The activation energy and drift mobility were calculated from the temperature-dependent dc electrical resistivity measurements. The dielectric constant and dielectric loss tangent for all the samples were determined as a function of frequency, and the frequency range used was from 20 Hz to 3 MHz at room temperature. The samples prepared using the simplified sol-gel method have lower dielectric constant values compared to those of the samples prepared using the co-precipitation method, and those prepared by the former method are more suitable for high-frequency applications. For the magnetic properties, a vibrating sample magnetometer was used. Saturation magnetization and coercivity increased with an increase in sintering temperature.
Cr-doped Ni-Zn ferrite nanoparticles having the general formula Ni 0.5 Zn 0.5 Cr x Fe 2−x O 4 (x = 0.1, 0.3, 0.5) were prepared by the simplified sol-gel method. The structural and dielectric properties of the samples sintered at 750 ± 5 • C were studied. X-ray diffraction (XRD) patterns confirm the single-phase spinel structure of the prepared samples. The crystallite size calculated from the most intense peak (3 1 1) using the Debye-Scherrer formula was 29-34 nm. Scanning electron microscope images showed that the particle size of the samples lies in the nanometer regime. The dielectric constant (ε r ), dielectric loss tangent (tan δ) and ac electrical conductivity (σ ac ) of nanocrystalline Cr-Ni-Zn ferrites were investigated as a function of frequency and Cr concentration. The dependence of ε r , tan δ and σ ac on the frequency of alternating applied electric field is in accordance with the Maxwell-Wagner model. The effect of Cr doping on the dielectric and electric properties was explained on the basis of cations distribution in the crystal structure.
Strontium hexa-ferrite nanoparticles were prepared successfully by simple co-precipitation method. The XRD analysis confirmed the formation of single phase MFe12O19(M=Sr). Parameters such as crystallite size, lattice constant, X-ray density and porosity were calculated from the X-ray diffraction data. The crystallite sizes were in the range 12-26 nm. The temperature dependent dc electrical resistivity measurements showed that the material was highly. Dielectric constant and dielectric loss factor (tanδ) were measured in the frequency range 20Hz-3MHz. The anomalous behavior of dielectric loss revealed a very important behavior of the prepared sample of SrFe12O19in different frequency regions and that could be used for new applications of this material. The magnetic properties were determined from the hystersis loop obtained from vibrating sample magnetometer (VSM). The Curie temperature was determined by susceptometer. This material is potentially suitable for use as a recording medium in identification cards and credit cards and for the fabrication of permanent magnets.
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