Strain-Induced Oxygen Vacancies and Ferromagnetic Order Near the Interface in CaMnO3 Thin Films

In this work we have studied the structural and magnetic properties of CaMnO
3
thin films grown over SrTiO
3
(100) substrates and
$\mathbf{BaTiO}_{\mathbf{3}}$
underlayers. These films are subject to a biaxial tensile strain due to a lattice mismatch of 4.8% or 7.2% between the CaMnO
3
and the respective underlayer. We have performed a systematic study of the manganese valence state throughout the thickness of the films and found correlations with their magnetic properties. Specifically, we have established that there is a concentration of Mn
⁺³
ions near the interface with the substrate that leads to an enhancement of a ferromagnetic order. We conclude that oxygen vacancies generate in this interface as a mechanism to release stress. According to the amount of oxygen vacancies, other magnetic phases may dominate the ground state.