Preparation And Properties Of Lead-free Magnetoelectric Composite Films BCZT/CZFO

Magnetoelectric (ME) thin films, which simultaneously exhibit ferroelectricity and ferromagnetism, have very wide applications in the next-generation novel multifunctional devices (e.g., memories, spintronic devices and magnetoelectric coupling devices, etc.) owing to the fact that they can be readily compatible with microelectronic devices and can reduce the sizes of the devices. In this work, the ferroelectric thin films ((Ba0.85Ca0.15)(Zr0.1Ti0.9)03(BCZT)), ferromagnetic thin films (Co0.8Zn0.2Fe2O4(CZFO)) and magnetoelectric composite thin films (Co0.8Zn0.2Fe2O4 /(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3(CZFO/BCZT)) were prepared via sol-gel process.Firstly, the CZFO thin films were deposited on Si(001) substrate and Pt(111)/Ti/SiO2/Si substrate via a sol-gel process and the microstructure and magnetic properties were investigated in this work. The results indicate that the CZFO thin films, which were deposited on the above substrates and annealed at 650℃, are both identified to be well-crystallized single phase (inverse spinel structured CFO) and exhibit no preferred orientation. The CZFO thin film deposited on Pt(111)/Ti/SiO2/Si substrate, by contrast, exhibit a more compact microstructure. Raman spectra reveals that the stresses in the deposited thin films are all shown to be compressive. In contrast, the CZFO thin film deposited on Si(001) substrate exhibits much higher compressive stress, and whereas the CZFO thin film deposited on Pt(111)/Ti/SiO2/Si substrate exhibits lower coercive field (Hc).Subsequently, BCZT thin film without seed layer and BCZT thin films with TiO2 and LaNiO3 seed layers were prepared on Pt(111)Ti/SiO2/Si substrates by sol-gel process. It is found from XRD characterizations that the BCZT thin films with TiO2 seed layer and LaNiO3 seed layer exhibit (111) and (h00) preferred orientation respectively. By contrast, LaNiO3 seed layer improves the crystalline quality of the BCZT thin films more obviously, and more specifically, the surfaces of the films with LaNiO3 seed layer are shown to be more compact and smoother. Furthermore, the BCZT thin films with LaNiO3 seed layer exhibit higher dielectric permittivity and lower dielectric loss.In the end, lead-free multilayered (2-2 type)magnetoelectric composite thin films (BCZT/CZFO) with different thicknesses of CZFO film were prepared and the microstructure, magnetic properties, electrical properties and magnetoelectric coupling properties of the composite films were investigated. It is shown that the prepared composite thin films exhibit good crystalline qualities and clear interfaces, that is, there is no obvious stratification and mutual diffusion in the films. With increasing the thicknesses of CZFO films in the composite films, the coercive electric field (Ec), saturation magnetization (Ms), remanent magnetic field (Mr) and magnetoelectric voltage coefficient (aE) increase, whereas the coercive magnetic field (Hc) decreases correspondingly.