1-x , where x = 0.00, 0.02, 0.04, 0.06 and 0.08 were prepared by the double sintering ceramic technique. Real part of the initial permeability µ', Curie temperature T c , imaginary part of the initial permeability µ", relative quality factor (Q-factor) of the samples were elaborately discussed as a function of frequency and temperature with increase of Fe-deficiency during the heating and cooling cycles.The temperature dependence of the imaginary part of the complex permeability curves are very interesting to note that there is a peak value of µ" at particular temperature which corresponds to the T c because at this temperature the samples might be in complete spin disorder. This reflects that at T c , a ferrimagnetically ordered state over comes K B T and becomes comparable with µ 0 H where the loss becomes maximum. Results of heating and cooling cycles were found to be very close to each other. The small difference during heating and cooling process might arise due to the thermal hysteresis which is accumulated in this work. In our study, it was noticed that the resonant frequency and T c increases first with the increase in iron deficiency and decreases after it takes a maximum at x = 0.06.
Chromium (Cr) doped strontium hexaferrites with nominal composition SrFe 12-x Cr x O 19 (x = 0.0, 0.1, 0.2, 0.3) were prepared using co-precipitation method. Thermal analysis of the samples was carried out using thermogravimetric analysis and differential scanning calorimetry to study the thermal stability as well as the transitions within the samples with variation in temperature. Structural analysis of the samples was carried out using X-ray diffraction (XRD). XRD revealed that all the samples possess hexagonal structure with space group P63/ mmc. AC electrical properties including dielectric constant (e 9), dielectric loss tangent (tan d) and ac electrical conductivity (r ac ) were studied as a function of frequency (1 kHz-3 MHz) at temperatures 100-700°C. The dielectric losses tend to decrease with increasing Cr content. AC conductivity could be very well explained by Jonscher power law. These materials have applications in high frequency devices with reduced energy losses.
Chromium doped strontium hexaferrites with the general formula SrFe 12-x Cr x O 19 having chromium contribution; x= 0.0, 0.1, 0.2, 0.3 were prepared by co-precipitation method. All the samples were calcined at 910ºC for 20 minutes and then sintered at 920ºC for 20 minutes. Structural analysis was done on these samples by X-Ray diffraction (XRD). Using XRD data crystal structure, phase purity and crystallite size were determined. The final structure of the materials under study was hexagonal. The observed crystallite sizes by using Scherrer formula were in the range from 40 to 52 nm. Morphological analysis was done by scanning electron microscopy (SEM) and by this the nature of the nanomaterials under study was found out to be particle i.e. nanoparticles. The dielectric constant, dielectric loss tangent and AC electrical conductivity of the samples were determined as a function of frequency at different temperatures from 100ºC to 700ºC, with the step of 200ºC. DC electrical resistivity was also done as a function of temperature. The investigation results of the AC electrical properties showed that with increase in temperature the magnitude of dielectric constant is increasing but is decreasing with increase in frequency. The trend of the dielectric loss was observed to be increasing with the increase in temperature. The AC electrical conductivity increases with the increase in temperature due to the phenomenon of enhanced hopping. The DC electrical resistivity graphs proved that with the increase in temperature the resistivity decreases and conductivity increases. All the electrical properties showed a strong correlation with structural properties. With the addition of chromium, resistivity of the materials increased, indicating lower energy losses due to eddy currents. Reduced eddy current losses make the chromium doped strontium hexaferrites, a potential candidate for efficient devices operated at high frequencies.
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