Ferromagnetic and insulating behavior of LaCoO3 films grown on a (001) SrTiO3 substrate: A simple ionic picture explained ab initio

This paper shows that the oxygen vacancies observed experimentally in thin films of ${\mathrm{LaCoO}}₃$ subject to tensile strain are thermodynamically stable according to ab initio calculations. By using DFT calculations, we show that oxygen vacancies on the order of 6% forming chains perpendicular to the (001) direction are more stable than the stoichiometric solution. These lead to magnetic ${\mathrm{Co}}²⁺$ ions surrounding the vacancies that couple ferromagnetically. The remaining ${\mathrm{Co}}³⁺$ cations in an octahedral environment are nonmagnetic. The gap leading to a ferromagnetic insulating phase occurs naturally and we provide a simple ionic picture to explain the resulting electronic structure.