Interface exchange processes in LaAlO$_3$/SrTiO$_3$ induced by oxygen vacancies

Abstract: Understanding the role of defects in oxide heterostructures is crucial for future materials control and functionalization. We hence study the impact of oxygen vacancies (OVs) at variable concentrations on orbital- and spin exchange in the LaAlO$3$/SrTiO$_3$ interface by first principles many-body theory and real-space model-Hamiltonian techniques. Intricate interplay between Hubbard $U$ and Hund's coupling $J{\rm H}$ for OV-induced correlated states is demonstrated. Orbital polarization towards an effective $e_g$ state with predominant local antiferromagnetic alignment on Ti sites near OVs is contrasted with $t_{2g}(xy)$ states with ferromagnetic tendencies in the defect-free regions. Different magnetic phases are identified, giving rise to distinct net-moment behavior at low and high OV concentrations. This provides a theoretical basis for prospective tailored magnetism by defect manipulation in oxide interfaces.