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

## TL;DR

This study uses ab initio calculations to explain the stability of oxygen vacancies in LaCoO3 films on SrTiO3, revealing a ferromagnetic insulating phase driven by vacancy formation and ionic interactions.

## Contribution

It demonstrates that oxygen vacancies stabilize ferromagnetic insulating behavior in LaCoO3 films, explained through a simple ionic model based on ab initio results.

## Key findings

- Oxygen vacancies of about 6% are thermodynamically stable.
- Vacancies form chains perpendicular to the (001) surface.
- Vacancies induce ferromagnetic coupling among Co2+ ions.

## Abstract

This paper shows that the oxygen vacancies observed experimentally in thin films of LaCoO3 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 Co2+ ions surrounding the vacancies that couple ferromagnetically. The remaining Co3+ cations in an octahedral environment are non magnetic. The gap leading to a ferromagnetic insulating phase occurs naturally and we provide a simple ionic picture to explain the resulting electronic structure.