Dual control of magnetism in LaMnO<sub>3</sub>/BaTiO<sub>3</sub> superlattice by epitaxial strain and ferroelectric polarization

The controlling of magnetism of perovskite oxides is scientifically interesting and technically important for numerous functionalities in spintronic devices and next-generation magnetic memories. The experimenally prepared superlattices often contain strain, polarization, oxygen vacancy and other factors, which can affect their magnetic properties. The magnetism of superlattice materials, controlled by using both epitaxial strain and ferroelectric polarization, is not only close to the real state of the material, but also can induce rich physical properties. In this work, we demonstrate a strong magnetoelectric coupling that appears in the LaMnO₃/ BaTiO₃ superlattice. First-principles calculations reveal that the reversible transitions among ferromagnetism, ferrimagnetism and anti-ferromagnetism are achieved by precisely controlling the magnitude and spin-direction of the magnetic moments of the Mn ions. A maximal change can be achieved to be 100.1% of the net magnetization by switching the ferroelectric polarization, which is much higher than the previous value 93.9%. The half-metallicity is demonstrated in the MnO₂ layer, and accompanied by the spin polarization of the superlattice varying from 100% to 0. In addition, we realize the coexistence of ferroelectric polarization and metallicity, i.e. “ferroelectric metal”. Neither of the strong covalent Mn—O bond and La—O bond acts as an obstacle that prevents the ferroelectric polarization from penetrating the LMO layer. The Jahn-Teller effect, the tilt and rotation of oxygen octahedron, and the charge transfer of the superlattice are systemically analyzed. The variation of strain and re-orientation of polarization lead the electrons to transfer between the e_g and t_2g orbitals of Mn, which determines the magnetism of our system. Our purpose-designed LMO/BTO superlattice with robust intrinsic magnetoelectric coupling is a particularly interesting model system that can provide guidance for developing the spintronics for future applications.