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The rare-earth element Yb3+-substituted β-ferrites KFe11−xYbxO17 with composition (x = 0, 0.02, 0.06 and 0.1) have been synthesized by sol–gel auto combustion method and sintered at 950 °C. X-ray diffraction (XRD) analysis divulged the formation of single phase β-hexagonal ferrites structure for the whole series. The crystallite size varied in the range of 26–43 nm for all samples. FTIR spectra showed absorption bands at different wave numbers which also confirmed the single phase of the samples. The samples had high dielectric constant, dielectric loss, and tangent loss values at lower frequencies while these values declined with increase in frequency. This dielectric behavior of the samples had been explained on the basis of Maxwell–Wagner and Koop’s model. The dielectric constant results were fitted theoretically by using Debye function which indicated the involvement of more than one ion in dielectric relaxation process. The AC conductivity increased with the increase of frequency and the nonlinear fitting of AC conductivity was obtained through Jonscher’s power law that followed conduction model exactly. The semicircle of cole–cole plots adumbrated the contribution of both grains and grain boundaries to the resistive and capacitive behavior of the material.

A series of rare earth elements (RE = Ce, Dy, Yb, La and Pr) substituted Sr0.9RE0.1Mn2Fe4O11 R-type hexagonal ferrites has been prepared by using the Sol–gel technique. The effect of RE substitution on its structural, electric polarization, dielectric and microwave absorption properties was studied. XRD patterns showed that all the prepared samples possess R-type hexagonal structure. The lattice parameters and unit cell volume varied with the substitution of RE contents. The average crystallite size, measured by Scherer formula, varied in the range of 6–15 nm for all samples. These results make this material suitable for being used in multilayer chip inductors (MLCI’s). The dielectric constant was found to decrease at high frequencies. This behavior has been explained on the basis of Maxwell–Wagner’s and Koop’s theory. An increase in AC conductivity was observed with increase in frequency. The decrease in lossy behavior with RE substitution in pure sample indicated the increase in the resistive nature of samples as observed from the electric polarization analysis. The Yb substituted sample exhibited highest value of microwave absorption − 40.5 dB at 11.4 GHz frequency among all the substituted samples.

This research project was designed to understand the synergistic effect of Mg2+ and Yb3+ ions substitution on structural, dielectric, electrical resistivity and electrical polarization properties of Sr1-xMgxFe4-yYbyMn2O11 (x = 0, 0.1, 0.2, 0.3 and y = 0, 0.02, 0.06, 0.1) R-type hexagonal ferrites prepared via sol–gel auto combustion method. The XRD graphs revealed that the present synthesized material exhibited the single phase. The Rietveld refinement was also carried out to fit XRD patterns which confirmed the single phase for all samples. The SEM micrographs indicate the platelet like structure for the grains. The curve fitting of real and imaginary part of permittivity results was done by using the modified Debye function. The ac conductivity enhanced with frequency. The electrical resistivity, calculated in the voltage range of (-200 V to 0 V) and (0 V to 200 V) was found to vary with Mg-Yb substitution. The P-E loops for each concentration unveiled the loosy behavior.

In the present investigation, the divalent basic element “Sr2+” was replaced with another divalent element “Mg2+” to understand the influential effect of Mg2+ on structural, electrical, dielectric and FTIR properties of Sr2+ based R-type hexagonal ferrites Sr1-xMgxFe4Sn2O11 with composition (x = 0.0, 0.1, 0.2, 0.3). The material was synthesized by sol-gel auto combustion method and sintered at 800 °C temperature for development of the required phase. The XRD and FTIR analysis revealed the formation of single-phase R-type hexagonal ferrites. It was observed that the values of lattice parameters a (A), c (A), crystallite size (nm), X-ray density (g/cm3) and unit cell volume V (A) 3 changed with Mg2+ substitution. The Scherer formula was used to find the crystallite size which varied in the range from 11 to 13 nm for all synthesized samples. The FTIR spectra also indicated the presence of negligible amount of moisture and Nitrogen in sample, absorbed from the atmosphere. The dielectric constant results showed the higher values for Mg2+ substituted samples than the pure sample. Furthermore, Debye function was used for the fitting of the dielectric constant results which indicated the participation of more than one ion in the increment of dielectric constant. The AC conductivity increased with the increase of frequency, consequently the experimental result was compared with theoretical results by Jonscher's power law which elicited the conduction mechanism. The P-E (polarization vs. electric field) loops substantiated the decrease in saturation and remnant polarization with Mg+2 content. The electrical resistivity of synthesized sample unveiled the resistive nature of sample significantly. It is suggested that the present R-type ferrites are useful in microwave absorption devices and in transformer to reduce the eddy current losses.

This research article reports the exploration of structural, dielectric, optical and electrical polarization properties of β-type hexagonal ferrite KLaxFe11-xO17 upon the substitution of rare earth element La3+ with compositions (x = 0, 0.02, 0.06 and 0.1). The samples were synthesized by adopting the sol-gel auto-combustion technique and the sintering temperature was 950 °C. The XRD patterns revealed the single hexagonal phase for all the samples. The lattice parameters a (A), c (A), crystallite size (nm), X-ray density (g/cm3) and unit cell volume V (A) 3 changed with La3+ substitution. The crystallite size was found to be varied in the range from 24 to 27 nm for all samples as calculated from Scherer formula. Fourier transform infrared spectroscopy (FTIR) spectra also confirmed the single phase for the synthesized samples. The dielectric constant exhibited the higher values than the pure sample with substitution. The dielectric constant results were fitted with the Debye function which indicated the participation of more than one ion in the increment of dielectric constant. The real (M′) and imaginary (M″) part of complex modulus graphs delineated the peaks shifting towards high and low frequency region which confirmed the occurrence of relaxation phenomenon in material. The polarization verses electric field loops corroborated the decrease in saturation and remnant polarization with La3+ contents. The P-E loops also showed the lossy behavior and the increment in lossy behavior with substitution pointed out the increase in resistivity of the samples. From aforementioned evidences, it is confirmed that the present synthesized beta ferrites are useful in the fabrication of humidity sensors and to reduce the eddy current losses.

A series of rare earth Pr3+ element substituted, Sr1-xPrxMn2Fe4O11 (x = 0, 0.02, 0.06, 0.1) R-type hexagonal ferrites has been synthesized by adopting the Sol-gel method. The influence of Pr-substitution on its structural, electrical, dielectric and magnetic behavior was examined. XRD patterns indicate the single phase for all the samples. The lattice parameters and unit cell volume changed with the substitution of Pr3+ contents. The electrical resistivity of the sample significantly varied with the substitution of Pr3+ ions. The sample with the Pr3+ concentration x = 0.1 was observed to have highest resistivity among the others. The dielectric constant was found to decrease at high frequencies for all samples. The tangent loss revealed the hopping type conduction between Fe3+ and Fe2+ sites. The increase in AC conductivity was observed as a function of frequency. The sample with concentration x = 0.1 revealed the maximum value of polarization. A peculiar magnetic trend was observed for all samples upon the substitution of Pr-contents. The unsubstituted sample exhibited the soft ferrimagnetic properties while the paramagnetic behavior was observed for Pr concentration x = 0.02 and last two concentrations (x = 0.06 and 0.1) unveiled the superparamagnetic nature.