Effects of molar ratio on dielectric, ferroelectric and magnetic properties of Ni0.5Zn0.5Fe2O4-BaTiO3 composite ceramics

Ni0.5Zn0.5Fe2O4-BaTiO3 (NZFO-BTO) magnetoelectric composite ceramics with different molar ratios (m(NZFO):(n(BTO) = 1:1.5, 1.5:1 and 2:1, defined as N1B1.5, N(1.)5B(1) and N2B1, respectively) were prepared successfully by using a joint hydrothermal method and sol-gel technique and sintering at 1000 degrees C. Meanwhile, the dielectric, ferroelectric and magnetic properties of the composites were investigated. The presence of bi-phase structure in the composites was verified with X-ray diffraction analyses. The scanning electron microscopy images and energy dispersion spectrum results confirmed that the bulk-like grains (2 to 5 mu m) and spherelike grains (similar to 0.5 mu m) could be attributed to NZFO and BTO, respectively. The dielectric constant and loss increased with increasing NZFO/BTO molar ratio because the carrier concentration of NZFO is higher than that of BTO. Thus, the dielectric constant of the N2B1 ceramics is more than 7800 at low frequency of 100 Hz and room temperature, while only less than 2000 for the N1B1.5 composite. Two peaks can be observed in the temperature dependence of the dielectric constant curves. One is near 120 degrees C, which corresponds to the Curie temperature of BTO, while the other peak occurs at about 320 degrees C, corresponding to the relaxation polarization. The remanent polarization increases with increasing the content of ferroelectric BTO. The maximum value at 1 kHz was observed for the N1B1.5 sample and it is larger than 4.5 mu C/cm(2), while the minimal value was obtained for the N2B1 composite and is only 1.2 mu C/cm(2). Magnetic properties were also measured and it was observed that magnetization increases with increasing the molar ratio. The largest saturation magnetization has the N2B1 composite (similar to 51.74 emu/g) due to the larger concentration of NZFO phase. However, the sample N1B1.5 shows the largest coercive field due to the highest interface interaction. This study provides guidelines for the fabrication of NZFO-BTO magnetoelectric composite ceramics.