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In the present study, we report a significant magnetoelectric coupling in lead-free (1-x)Ba0.95Ca0.05Ti0.95Sn0.05O3 - (x)Ni0.7Zn0.3Fe2O4 (x = 0.10, 0.15, 0.20, 0.25 and 0.30) particulate composites prepared by solid-state route. Phase purity and crystal structure of the composites were examined by the X-ray diffraction measurement. With the incorporation of the magnetic NZFO phase, a decrease in the tetragonality of the ferroelectric BTCS lattice was confirmed by the full pattern match of the XRD data using Rietveld analysis. FESEM micrographs revealed improved microstructures with the addition of ferrite concentrations in the composites. Simultaneous presence of ferroic orders in the composites was confirmed from the room-temperature P-E and M-H hysteresis loops. Direct magnetoelectric voltage measurement of the composites established the strain-mediated coupling between the BTCS and NZFO phases. Highest RT first-order magnetoelectric voltage coefficient (α/d = 6.24 mV/cm-Oe) of the x = 0.25 composite is attributed to better individual ferroic properties and improved microstructure of this sample. [ABSTRACT FROM AUTHOR]

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]

We investigated the anomalous behaviour in the dielectric properties, occurring nearly at room temperature and at elevated temperatures (near the Neel temperature TN) of the polycrystalline samples of YFeO3 (YFO) ceramics. On the prepared YFO ceramics, the magnetic measurements showed the Neel temperature of YFO to be 650 K, below which the compound exhibited the weak ferromagnetic behaviour. X-ray photoelectron spectroscopy (XPS) shows the presence of Fe ions (Fe2+ and Fe3+ states) and also revealed the formation of the oxygen vacancies. The frequency dependence of the complex dielectric constant within the frequency domain of 100 Hz–1 MHz shows the presence of grain dominated dielectric relaxation over the thermal window of 300–373 K. The activation energy E act. ε = 0.611 eV extracted from the imaginary permittivity spectrum indicates the involvement of oxygen vacancies in the relaxation process. Above 493 K, the ac conductivity, complex impedance, and modulus studies revealed appreciable conduction and relaxation processes occurring in YFO ceramics with respective activation energies E a c t. σ = 1.362 eV and E a c t. Z = 1.345 eV , which suggests that the oxygen vacancies are also involved for the anomalous behaviour of the dielectric constant at elevated temperatures. The temperature dependent Raman spectroscopic measurements within the thermal window of 298–698 K showed anomalous variations of the line widths and frequencies of several Raman active modes above 473 K up to the vicinity of TN pointing towards the presence of admixtures of the electron-phonon and spin-phonon coupling in the system. A further study on the thermal variation of the B2g(4) mode frequency with [M(T)/MS]2 shows the occurrence of strong spin–phonon (s-p) coupling, while the line shape shows the presence of the Fano asymmetry, suggesting spin dependent electron-phonon (e-p) coupling in the system below TN. [ABSTRACT FROM AUTHOR]