Atomic and electronic structure of La₂CoMnO₆ on SrTiO₃ and LaAlO₃ substrates from first principles

Adhesion energies, atomic structures, electronic states, and bonding nature of the La₂CoMnO₆(001)/SrTiO₃(001) and La ₂CoMnO₆(001)/LaAlO₃(001) interfaces are systematically investigated from first principles by taking into account strain effect, electron correlation effect, and polarity continuity. A total of sixteen candidate geometries are considered for each interface, and the fundamental impact of strain on interfacial atomic structures is found to be minor, but its electronic impact is significant. For the La₂CoMnO ₆/SrTiO₃ interface where La₂CoMnO₆ suffers tensile strain, the 3d states of Co and Mn overlap Fermi level, demonstrating a metallic nature for this interface. Electrons are found to be injected into the Ti of SrTiO₃ at this interface and spread layers away from interface, inducing an ordering of the in-plane d_xy orbital. On the other hand, the compression strained La₂CoMnO ₆/LaAlO₃ interface takes on a half-metallic nature with a large degree of hybridization of interfacial Mn 3d with O 2p at Fermi level. We also find an ordering of the out-of-plane d_z² orbital for the interfacial and sub-interfacial Mn atoms and an ordering of the p _z orbital for the O neighboring Mn. By applying several analytic methods, we have thoroughly characterized the electronic structure and have determined the interfacial bonding to be covalent for the La ₂CoMnO₆/SrTiO₃ interface, yet mixed covalent and ionic for the La₂CoMnO₆/LaAlO₃ interface.