Effect of Magnetic Phase on Structural and Multiferroic Properties of Ni1−xZnxFe2O4/BaTiO3 Composite Ceramics.

Ni_1−xZn_xFe₂O₄/BaTiO₃ (x = 0.3, 0.4, 0.5, 0.6, and 0.7) magnetoelectric composite ceramics have been prepared by combining the coprecipitation and sol–gel methods, and their structural and multiferroic properties studied and compared. The results indicate that the synthesized composites present biphase and composite structure, with no evident impurities observed. The lattice of the Ni_1−xZn_xFe₂O₄ crystal structure is distorted owing to the incorporation of Zn²⁺ ions. The samples present irregular microstructure and abnormal grain growth, which can be attributed to the heterogeneous distribution of the ferroelectric and magnetic phases during preparation. The chemical composition of the larger grains is Ni_1−xZn_xFe₂O₄, while that of the smaller grains is proven to be BaTiO₃. The dielectric constant of the ceramics first increases then decreases as the Zn²⁺ ion content is increased, which is related to the irregular microstructure of the ceramics. Both the frequency dependence of the dielectric loss and the temperature dependence of the dielectric constant present two relaxation peaks for all samples. The dielectric loss peaks are attributed to the slow polarization process, such as turning-direction and space-charge polarization, while the dielectric constant peaks can be ascribed to the ferroelectric phase transition of BaTiO₃ and relaxation polarization of the composites. The abnormal magnetization behaviors can be induced by the A–B superexchange interaction caused by the addition of nonmagnetic Zn²⁺ ions. [ABSTRACT FROM AUTHOR]