Ab initio study of magnetism at the TiO2/LaAlO3 interface

TL;DR

This study uses ab initio calculations to explore how structural relaxation and oxygen vacancies at the TiO2/LaAlO3 interface influence electronic and magnetic properties, shedding light on the origin of unexpected magnetism in undoped TiO2 films.

Contribution

It provides a detailed ab initio analysis of the effects of oxygen vacancies and structural relaxation on magnetism at the TiO2/LaAlO3 interface, highlighting factors that induce magnetic behavior.

Findings

Oxygen vacancies alter Ti valence states but do not always induce magnetism.

Magnetism depends on structural details like second neighbor positions.

Both LSDA and LSDA+U methods confirm these effects.

Abstract

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.