Effect of core size on the magnetoelectric properties of Cu0.8Co0.2Fe2O4@Ba0.8Sr0.2TiO3 ceramics

Cu0.8Co0.2Fe2O4@Ba0.8Sr0.2TiO3 ceramics (@ stands for core-shell structure) were prepared by the sol-gel method, and the effects of the core size (20 nm, 40 nm, 50 nm, and 70 nm) on the microstructure, electrical properties, magnetic properties, and magnetoelectric coupling were studied. X-ray diffraction patterns show that Cu0.8Co0.2Fe2O4@Ba0.8Sr0.2TiO3 ceramics have a biphasic structure and only a small amount of Ba3Fe32O51 impurity phase exists when the core size is 70 nm. Scanning electron microscopy shows that the surface of all samples is relatively uniform except for a few holes and agglomerations. Transmission electron microscopy revealed an obvious shell-core structure, but the cladding effect became worse as the core size increased. The dielectric constant increases and the dielectric loss decreases with increase of the core size. However, as the core size increases, the change in the dielectric constant of the ceramic samples decreases with application of an external magnetic field. As the core size increases, the ferroelectric properties of the samples are gradually improved, and the ferroelectric properties are relatively good when the core size is 70 nm. The saturation magnetization (Ms), remanent magnetization (Mr), and coercive force (Hc) of the ceramics decrease with increase of the core size. As the core size increases, the magnetic domain switches more easily. The sample with a core size of 70 nm has strong magnetism, and its magnetoelectric coupling coefficient is about 78.14 V/cm·Oe.