Defect engineering of magnetic ground state in EuTiO₃ epitaxial thin films

Atomistic defect engineering through the pulsed laser epitaxy of perovskite transition metal oxides offers facile control of their emergent opto-electromagnetic and energy properties. Among the various perovskite oxides, EuTiO₃ exhibits a strong coupling between the lattice, electronic, and magnetic degrees of freedom, which is highly susceptible to atomistic defects. In this study, we investigated the magnetic phase of EuTiO₃ epitaxial thin films via systematic defect engineering. A magnetic phase transition from an antiferromagnet to a ferromagnet was observed when the unit cell volume of EuTiO₃ expanded due to the introduction of Eu–O vacancies. Optical spectroscopy and density functional theory calculations show that the change in the electronic structure as the ferromagnetic phase emerges can be attributed to the weakened Eu–Ti–Eu super-exchange interaction and the introduction of the ferromagnetic Eu–O–Eu interaction. Facile defect engineering in EuTiO₃ thin films facilitates understanding and tailoring of their magnetic ground state.