Ab initio study of the magnetoelectric effect and critical thickness for ferroelectricity in Co2FeSi/BaTiO3 multiferroic tunnel junctions

The interfacial magnetoelectric effect and the critical thickness for the ferroelectric in half-metallic ferromagnet/ferroelectric Co2FeSi/BaTiO3 multiferroic tunnel junctions are investigated using a first-principles density-functional theory. The magnetoelectric effect is derived from the difference of the magnetic moments on interfacial atoms, which are sensitive to the polarization of ferroelectric layers in multiferroic tunnel junctions. Besides this, the coupling is found to be dependent on the interfacial electronic hybridizations and to be affected by the choice of the atomic termination. In addition, the magnetoelectric coefficients calculated for the FeSi/TiO2 and Co-2/TiO2 interfaces of the junctions are different from each other. Meanwhile, the critical thickness of ferroelectric state was found to be about 1.7 nm in the Co-2/TiO2 interface but vanished in the FeSi/TiO2 interface. The half-metallic ferromagnetic/ferroelectric tunnel junctions may open a promising avenue for designing novel electronic and spintronic devices at nanoscale.