A comparative study on structural, dielectric and multiferroic properties of CaFe2O4/BaTiO3 core-shell and mixed composites

The core-shell CaFe2O4@BaTiO3 and (1−x) CaFe2O4 - xBaTO3 (x = 0.3, 0.5, 0.7) mixed composites were synthesized using a combination of solution processing and solid state reaction method respectively followed by high temperature calcinations. The presence of the constituent spinel-ferrite phases in both core-shell and mixed nanocomposites were confirmed by X-ray diffraction patterns and transmission electron microscopy. High-resolution transmission electron microscope images indicate a clear view of ferrite and ferroelectric phases in each core-shell and mixed composite, where the ME coupling effect of ferrite and ferroelectric phase happened. Dependence of dielectric constant (ε′), loss tangent (tan δ) and AC conductivity (σAC) with frequency (100 Hz-2 MHz) and temperature (25 °C-550 °C) with increasing probing frequency (1 kHz-2 MHz) of the composites have been investigated. The peak observed in mixed composites and core-shell nanostructures in the low temperature range (130 °C-150 °C) are attributed to ferroelectric to paraelectric phase transition of BaTO3. The second peak observed at high temperature attributed to TC (Curie temperature) of the ferrite (CaFe2O4) phase. The core-shell composite did not show any magnificent improvement in dielectric properties than mixed composites. The presence of ordered FE and FM behavior at room temperature was confirmed by observation of P-E and M-H hysteresis loops; respectively and core-shell composite shows drastic improvement in ferroelectric, magnetic and magneto-electric properties than the mixed composites. In addition, the calculated linear ME coupling coefficient results reveal strong ME coupling effect and the maximum recorded value is ∼30.32 mV/cmOe for the core-shell composite. The larger value of ME coupling coefficient may arise from larger saturation magnetization and remnant magnetization of the core-shell composite.