Positive Magneto‐Electric Couplings in Epitaxial Multiferroic SrMnO$_3$ Thin Film

This study demonstrates the magneto-dielectric (MD) properties of high quality epitaxially strain multiferroic SrMnO$_3$ thin film on conducting Nb doped SrTiO$_3$ substrate. The study observes considerable high positive MD coupling near room temperature and across the anti-ferromagnetic transition temperature of SrMnO$_3$. 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 SrMnO$_3$ 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 Mn$^{4+}$, Mn$^{3+}$, and Mn$^{2+}$ in the grown films. Despite having mixed Mn states, SrMnO$_3$ thin films remain in the insulating phase. So, the insulating nature of SrMnO$_3$ 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 SrMnO$_3$ thin film by change in oxygen vacancy induced modification in crystal field.