Decisive role of oxygen vacancy in ferroelectric versus ferromagnetic Mn-doped BaTiO₃ thin films

Single-phase perovskite 5 at.% Mn-doped and undoped polycrystalline BaTiO₃ thin films have been grown under different oxygen partial pressures by pulsed laser deposition on platinum-coated sapphire substrates. Ferroelectricity is only observed for the Mn-doped and undoped BaTiO₃ thin films grown under relatively high oxygen partial pressure. Compared to undoped BaTiO₃, Mn-doped BaTiO₃ reveals a low leakage current, increased dielectric loss, and a decreased dielectric constant. Ferromagnetism is seen on Mn-doped BaTiO₃ thin films prepared under low oxygen partial pressure and is attributed to the formation of bound magnetic polarons (BMPs). This BMP formation is enhanced by oxygen vacancies. The present work confirms a theoretical work from C. Ederer and N. Spaldin on ferroelectric perovskites [Nature Mat. 3, 849 (2004)] which shows that the existence of ferroelectricity is incompatible with the existence of a spontaneous magnetization in Mn-doped BaTiO₃ thin films.