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We report the effect of Co3+-Ti4+ doped SrFe12-(x–y)CoxTiyO19 (x = y = 0.0, x = 0.225, y = 0.1125) hexaferrite successfully prepared using the conventional ceramic route. The structural, optical, electrical, and magnetic properties were analyzed via X-ray diffraction, scanning electron microscopy, diffuse reflectance spectroscopy, complex impedance spectroscopy, and vibrating sample magnetometer. The structural analysis (Rietveld Refinement) revealed that all the samples exhibit magnetoplumbite hexagonal crystal structures with P63/mmc space group. At the same time, their increase in grain size and the bandgap energy showed evidence of dependency on Co3+-Ti4+ content in SrFe12O19. The impedance and modulus spectra showed the suppression of surface charge polarization with substituting Co3+-Ti4+ ions and co-contribution of the grain and grain boundary effect presented by modeling the electrical processes using an equivalent circuit model. Two transition peaks were observed in the temperature-dependent dielectric constant plots, represented as Td and Tm. However, Tm is nearly frequency-independent, and only one transition peak is identified in frequency versus dielectric constant plots. The temperature Td is due to dipole relaxation, whereas Tm is assigned as dielectric phase transition, modeled by modified Curie–Weiss law. Further, the AC conductivity was examined by Jonscher’s powder law and random free energy barrier model, showing that the AC conductivity increases by increasing frequency due to electronic and overlapping large-polaron hopping mechanisms. Finally, in the magnetic measurements, a simple phenomenological model was modeled based on the Lorentzian function model, representing a transition from hard to soft ferrites in the doped Co3+-Ti4+ SrFe12O19 with saturation magnetization of 123.66 emu/g and coercivity of 316.69 Oe. [ABSTRACT FROM AUTHOR]

In this work, effect of sintering temperature on magnetoelectric properties of lead-free [85 wt% Ba0.95Ca0.05Ti0.95Sn0.05O3 (BTCS)–15 wt% Ni0.7Zn0.3Fe2O4 (NZFO)] particulate composite has been studied. The composites were synthesized by solid-state reaction method and sintered at five different temperatures. Structure analysis of constituent phases of the composites has been examined by X-ray diffraction (XRD) technique. Rietveld refinement confirmed that the piezoelectric BTCS comprised two phases (tetragonal and orthorhombic) and inverse spinal NZFO has a cubic phase in the composites. Surface morphology study carried out by Field Emission Scanning Electron Microscope (FESEM) accounted the increase in uniform grain size and connectivity of the constituent phases with the increase of sintering temperature. Dielectric constant vs. temperature (Ɛr–T) graph showed two anomalies corresponding to the ferroelectric transition temperature of BTCS and the magnetic transition temperature of NZFO phase. Enhancement in saturation polarization (PS) and decrease in saturation magnetization (MS) at room temperature were observed with the increase of sintering temperature. The composite, sintered at 1300 °C for 4 h showed maximum change in magnetodielectric value (MD% ∼ 1.94 at 100 kHz frequency) at room temperature. This sample also exhibited the highest first and second order magnetoelectric coefficients (α/d = 2.37 mV/cm-Oe and β/d = 40.69 µV/cm-Oe2) at room temperature which was explained on the basis of sintering temperature-dependent ferroic properties of the individual phases. [ABSTRACT FROM AUTHOR]