Effect of sintering temperature on magnetoelectric coupling in 0.2Ni0.9Zn0.1 Fe2O4-0.8Ba0.9Sr0.1 TiO3 composite ceramics

Magnetoelectric composites have attracted much attention due to their intriguing physical properties and potential applications. They might have strong magnetoelectric coupling effect above room temperature, but it mainly depends on the sintering schedule. In this paper, 0.2Ni(0.9)Zn(0.1)Fe(2)O(4)-0.8Ba(0.9)Sr(0.1)TiO(3) (NZFO-BSTO) composite ceramics were prepared by conventional solid sintering method. Effects of the sintering temperature (1050, 1100, 1150 and 1200 degrees C) on the microstructure, dielectric and multiferroic properties were investigated in detail. XRD results confirm that the prepared ceramics show bi-phase structure, which can be indexed as NZFO and BSTO. No obvious impurity phase was observed when the sintering temperature is less than 1200 degrees C, indicating that there is no apparent chemical reaction occuring at the magnetic and ferroelectric interface. All of the samples show relatively dense and uniform structure. The mean grain size of the composites increases from 220 to 650 nm when the sintering temperature increases from 1050 degrees C to 1200 degrees C. The sample ST-1100 has the best frequency stability of dielectric constant, while it presents the smallest dielectric loss. All specimens present two dielectric peaks, the first one is attributed to the diffuse phase transition of BSTO, while another one generated at higher temperature corresponds to the relaxation polarization. The sample ST-1100 shows excellent ferroelectric properties, the value of remnant polarization is about 5.1 mu C/cm(2) and the coercive electric field value is similar to 20 kV/cm. The ceramics ST-1050 and ST-1200 show larger leakage current. All samples show paramagnetic behaviour with small remnant magnetization (similar to 0.3 emu/g) and coercive magnetic field (similar to 30 Oe). The sample ST-1100 has maximum magnetoelectric coupling coefficient of 9.6 mV/cm.Oe when the magnetic field is near 1100 Oe.