Origin of unexpected lattice expansion and ferromagnetism in epitaxial EuTiO_3–δ thin films

This paper uses laser energy fluence as a single variable parameter to investigate the underlying mechanisms that explain the striking physical properties in EuTiO_3–δ (ETO_3–δ) thin films. Out-of-plane lattice expansion reveals a linear dependence with laser energy fluence, which induces horizontal cracks near the film/substrate interface. Interestingly, however, by post-annealing the substrate in a hydrogen atmosphere, the planar defects formed during film growth are removed, which suggests that these defects are related to laser energy and are thus created during the deposition. Ferromagnetic order also demonstrates a strong relationship with lattice expansion, which reveals a modulation effect from vertical strain that compensates for the negative effects that result from mixed-valence Eu³⁺. Ultimately, our results demonstrate that energy-induced defects can be used for manipulating ferromagnetism in antiferromagnetic perovskite systems.