Here, we report the structure evolution, magnetic and ferroelectric properties in Co-doped 4- and 3-layered intergrowth Aurivillius compounds Bi4NdTi3Fe1-xCoxO15-Bi3NdTi2Fe1-xCoxO12-δ. The compounds suffer a structure evolution from the parent 4-layered phase (Bi4NdTi3FeO15) to 3-layered phase (Bi3NdTi2CoO12-δ) with increasing cobalt doping level from 0 to 1. Meanwhile the remanent magnetization and polarization show opposite variation tendencies against the doping level, and the sample with x = 0.3 has the largest remanent magnetization and the smallest polarization. It is believed that the Co concentration dependent magnetic properties are related to the population of the Fe3+ -O-Co3+ bonds, while the suppressed ferroelectric polarization is due to the enhanced leakage current caused by the increasing Co concentration. Furthermore, the samples (x = 0.1–0.7) with ferromagnetism show magnetoelectric coupling effects at room temperature. The results indicate that it is an effective method to create new multiferroic materials through modifying natural superlattices.

To reduce trailing noises mixed in ultrasonic echoes during ultrasonic wave propagation in a buffer rod, the influence of the rod’s boundary shape and dimension on the signal-to-noise ratio (SNR) was analyzed using a simulation method. Novel buffer rods with complex structures and shapes based on a cylinder or cone reference surface were proposed. The novel rods were found to be more effective in obtaining signals with high SNR than the cylinder or cone rods currently in use. Simulation results showed that the rod proposed in this paper exhibited better performance in a given installation space compared with the cylinder or cone rods.