Positive Magneto-Electric Couplings in Epitaxial Multiferroic SrMnO3 Thin Film

This study demonstrates the magneto-dielectric (MD) properties of high quality epitaxially strain multiferroic SrMnO₃ thin film on conducting Nb doped SrTiO₃ substrate. The study observes considerable high positive MD coupling near room temperature and across the anti-ferromagnetic transition temperature of SrMnO₃. The dielectric maxima of the grown film is above room temperature, which confirms the room temperature ferroelectric nature of the grown film. From out-of-plan polarization and PUND (Positive Up Negative Down) measurements in the presence of magnetic field, it is confirmed that the polarization value of grown SrMnO₃ thin film increases with an increase in magnetic field. In this study, the oxygen off-stoichiometry concentration is also varied by varying oxygen partial pressure during deposition and is able to create Mn⁴⁺, Mn³⁺, and Mn²⁺ in the grown films. Despite having mixed Mn states, SrMnO₃ thin films remain in the insulating phase. So, the insulating nature of SrMnO₃ thin film is robust with respect to oxygen off-stoichiometry and vacancy/substrate induced strain mediated change in the crystal field. The study has also demonstrated the variation of MD in SrMnO3 thin film by change in oxygen vacancy induced modification in crystal field.