Electronic and magnetic properties of the interface LaAlO$_3$/TiO$_2$-anatase from density functional theory

Ab initio calculations using the local spin density approximation and also including the Hubbard $U$ have been performed for three low energy configurations of the interface between LaAlO$_3$ and TiO$_2$-anatase. Two types of interfaces have been considered: LaO/TiO$_2$ and AlO$_2$/TiO, the latter with Ti-termination and therefore a missing oxygen. A slab-geometry calculation was carried out and all the atoms were allowed to relax in the direction normal to the interface. In all the cases considered, the interfacial Ti atom acquires a local magnetic moment and its formal valence is less than +4. When there are oxygen vacancies, this valence decreases abruptly inside the anatase slab while in the LaO/TiO$_2$ interface the changes are more gradual.

Ab initio study of magnetism at the TiO2/LaAlO3 interface

In this paper we study the possible relation between the electronic and magnetic structure of the TiO2/LaAlO3 interface and the unexpected magnetism found in undoped TiO2 films grown on LaAlO$_3$. We concentrate on the role played by structural relaxation and interfacial oxygen vacancies. LaAlO3 has a layered structure along the (001) direction with alternating LaO and AlO2 planes, with nominal charges of +1 and -1, respectively. As a consequence of that, an oxygen deficient TiO2 film with anatase structure will grow preferently on the AlO2 surface layer. We have therefore performed ab-initio calculations for superlattices with TiO2/AlO2 interfaces with interfacial oxygen vacancies. Our main results are that vacancies lead to a change in the valence state of neighbour Ti atoms but not necessarily to a magnetic solution and that the appearance of magnetism depends also on structural details, such as second neighbor positions. These results are obtained using both the LSDA and LSDA+U approximations.