Study On Multiferroicity Of BaTiO₃/La_0.67Sr_0.33 MnO₃ Nanocomposite Films

Multiferroic materials are those in which two or more of the properties of ferroelectricity (antiferroelectricity), ferromagnetism (or antiferromagnetism, ferrimagnetism) and ferroelasticity coexist and coupled. This characteristic offers possibilities for manufacturing new multifunctional materials. In 1890s, by analyzing crystal symmetry, Pierre Curie predicted the possibility of an intrinsic magnetoelectric effect. The first successful observation of the magnetoelectric effect was realized in Cr₂O₃ by Astrov in the middle twentieth century, which indicated the emergence of the multiferroic material.Multiferroics are very sparse in nature. Besides, both the Curie temperature and the magnetoelectric coefficient of the nature multiferroics are low. Undeniable, these conditions are not conducive to practical applications. Recently, researchers make efforts to increase the magnetoelectric effect and Curie temperature through compositing the ferroelectric and ferromagnetic materials.Basing on our previous researches of the perovskite structures, we choose ABO₃ structural ferroelectric material (BaTiO₃) and ferromagnetic material (La_0.67Sr_0.33MnO₃) as targets through the pulsed laser deposition (PLD) technology preparing the multiferroic thin films and study the ferromagnetism and ferroelectrity. The main research contents are as follows.1. Preparation of the BaTiO₃ target and the characterization of the structure.BaTiO₃ powder were prepared by solid-state reaction, the measurements of X-ray diffraction indicate that the material is crystallizing in a tetragonal structure at room temperature. The prepared powder was pressed into target by extrusion die.2. Preparation of the BaTiO₃/La_0.67Sr_0.33MnO₃ bilayer thin films and the characterization of the structure, ferromagnetism and ferroelectricity.PLD technology was used for depositing BaTiO₃, La_0.67Sr_0.33MnO₃ and BaTiO₃/La_0.67Sr_0.33MnO₃ bilayer thin films on Si substrates. The BaTiO₃ target used in our paper are self-made and the La_0.67Sr_0.33MnO₃ target is purchased. All films are highly crystalline and the two phases of bilayer thin films keep their lattice structures respectively. The results of the measurements show that BaTiO₃/La_0.67Sr_0.33MnO₃ bilayer thin films have good ferromagnetism and ferroelectricity, the maximal remnant polarization and residual magnetization for the sample is 22.6μC/cm² and 2.33 emu/cm³. we observed the magnetoelectric coupling effect at the curie temperature of BaTiO3, the maximal magnetization hopping of LSMO isΔM_max = 1.55 emu/cm³.3. Preparation of the BaTiO₃/La_0.67Sr_0.33MnO₃ multi-layer films and the characterization of the structure, ferromagnetism and ferroelectricity.At the basis of preparation of the BaTiO₃/La_0.67Sr_0.33MnO₃ bilayer thin films, BaTiO₃/La_0.67Sr_0.33MnO₃ multi-layer films were prepared and the structure, magnetic, electric properties were compared. The magnetic-electric coupling effect is enhanced as the result of the increasing of the interfaces, and the maximal magnetization hopping of LSMO isΔM_max = 2.63 emu/cm3. However, interdiffusion between the two phases at interface can not be neglected. Too many layers will intensify this interdiffusion and increase leakage current, then deteriorate the ferroelectric property. Compare with the bilayer thin films, the multi-layer films have larger leakage current.