First-principles Investigation On Magnetoelectric Effect In Perovskite Oxides Interfaces

Perovskite oxides, is a natural calcium titanium oxide with ABO3structure. Several remarkable perovskite oxides superlattices are investigated using first-principles calculation to illustrate ferroelectric behavior at nanoscale as well as magnetoelectric effect within heterostructure interface.Using first-principles calculations, a systematic theoretical study on the nanoscale ferroelectricity of three-component superlattices (or tricolor superlattices, TCSs)ferroelectric films, SrTiO3-BaTiO3-CaTiO3(STO-BTO-CTO) is reported. We demonstrate that such structures have intrinsic asymmetric ferroelectricity, polarization in the typical two directions,"up" and "down", corresponding to the aptitude of polarization as well as the depth of potential energy profile. The theoretical results demonstrate that such intrinsic asymmetric ferroeletricity is the result of breaking compositional inversion symmetry. Futher investigation shows that there exists a certain relationship between the polarization directions and geometric stacking sequences of the superlattices,. Specifically, the lowest energy states always have polarizations direction, CTOâ†'BTOâ†'STO, while the sequence in the metastable states is STOâ†'BTOâ†'CTO. This intriguing properties may suggest a controllable way to fabricate ferroelectric tunnel junctions, which makes it possible to distinguish the two polarization direction with distinct energy state ("0"state and "1" state) by means of their geometric stackings, which is helpful to read storage information accurately. In order to further clarify if TCSs can be used to tunnel junctions, we also investigate ferroelectric stability of TCSs at nanoscale. We calculate TCS tunnel junctions with electrodes SrRuO3(SRO), and find that several TCS composite structures are ferroelectric, among which SRO/CBBS show larger ferroelectricity than SRO/CCBBSS and is more applicable to ferroelectric tunnel junctions. Furthermore, we also studied a ferroelectric-ferromagnetic multilayers, Fe/STO/Fe under compressive and expansive tensor stress. We found that such structure produces a magnetoelectric effect at the interface where induced Ti magnetic moment can be found because of the bonding effect between Ti, Fe and O atoms. Our study will provide a theoretical foundation for future fabrication of ferroelectric tunnel junctions and magnetic devices controlled by electric field.