Ab initio study of magnetism at the TiO2/LaAlO3 interface

In this article, we study the possible relation between the electronic and magnetic structures of the TiO2/LaAlO3 interface and the unexpected magnetism found in undoped TiO2 films grown on LaAlO3. 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 neighbor 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 local spin density approximation (LSDA) and LSDA + U approximations.