Low-firing behavior, microstructure, and electromagnetic properties of a ferroelectric-ferromagnetic composite material with multiple doping

A series of BaTiO3-Ni0.62Cu0.25Zn0.16Fe1.98O4 ferroelectric-ferromagnetic composites with Li2CO3-V2O5-Bi2O3 multiple doping were prepared by the solid-state reaction at 900 °C-1000 °C, and the low fired (<961 °C) samples can adapt to the low temperature cofired ceramic (LTCC) technology. The relative density of all sintered composites was higher than 96%, and particularly for the low fired composites, it was in the range of 97.1%-99.5%. The variation of magnetic properties with BaTiO3 content was investigated combining with microstructure and two types of magnetization (demagnetization) processes. A novel method for calculating the microstructure parameter δ∗/D of the multiple doping composite systems has been deduced so that the magnetic circuit model can be used to predict the magnetic properties of the composites, and the experimental results matched well with the fitting curve. The dielectric behavior of the composites has been investigated in non-dispersive region (106∼108 Hz) and dielectric dispersion region (108∼1010Hz). Through combing grain size effect and phase transition, the influence of sintering temperature and BaTiO3 content on permittivity ε′ and dielectric dispersion of the composites have been discussed. In the non-dispersive region, the maximum ε′ of composites (256.07) was obtained in the sample with 90 wt% BaTiO3 (sintered at 950 °C). In the dispersion region, among all composites, both the maximum relaxation frequency 1.24 GHz and maximum resonance frequency 1.16 GHz were obtained in low fired samples.