by Su Chul Yang
My research focuses on the lead-free magnetoelectric (ME) materials for potential applications as shown in Figure 1. The lead-free ME materials are categorized into three groups: (i) single-phase materials, (ii) 3-0 type particulate composites, and (iii) 2-2 type laminate composites. For high ME effect, we have been developing various lead-free materials based on BaTiO3 and (K0.5Na0.5)NbO3. Especially, self-biased ME effect induced by both magnetic interactions and bending effect have been studied for low-powered/high sensitive sensors and devices.In order to increase the ME effect, we have been developing various compositions for lead-free materials based on BaTiO3 and (K0.5Na0.5)NbO3. Our study on the lead-free (1-x)BaTiO3-xBiFeO3 single-phase ME materials were conducted by varying compositions and the composites were found to exhibit high ME coefficient at room temperature in off-resonance conditions. The 3-0 particulate lead-free (1 - x) [0.948 K0.5Na0.5NbO3 – 0.052 LiSbO3] – x Ni0.8Zn0.2Fe2O4 (KNNLS-NZF) ME composites were synthesized by sintering with rigid inclusion and were found to exhibit dense island-matrix structure with relative density of > 95% and high ME coefficient of 20 mV/cm Oe at 1 kHz. Figure 3 shows the schematic diagram for island-matrix structures by sintering with rigid inclusion and the SEM images in Figure 4 show the island-matrix structure for KNNLS-NZF composites. Recently, we report self-biased ME effect in three-phase lead-free ME laminates by both magnetic interactions and bending effect. The ME laminates were prepared using one-phase piezoelectric and two-phase magnetostrictive materials and the self-biased ME effect, which is a remnant ME coefficient at zero magnetic bias, was found to be experimentally demonstrated. Figure 5 shows the ME hysteresis in three phase lead-free ME unimorph and bimorph laminates and the hysteresis can be used for attractive applications such as low-powered/high sensitive sensors and electrically turned memory devices.