Understanding defect-mediated cubic to hexagonal topotactic phase evolution in SrMnO3 thin films and associated magnetic and electronic properties

Abstract

The coupling between the oxygen stoichiometry and strain-induced lattice distortions has huge bearings on the electronic and magnetic properties of $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3}$ (SMO). In this paper we have observed oxygen stoichiometry-mediated epitaxial tetragonal to nonepitaxial-oriented hexagonal topotactic phase transition of $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3}$ thin film on $\mathrm{SrTi}{\mathrm{O}}_{3}$ (100) substrate. The oxygen stoichiometric hexagonal SMO films are oriented in nature, while the oxygen-deficient epitaxially strained $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ films are tetragonal in nature. It is observed that oxygen vacancy is obligatory to hold on the epitaxial strain in $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ thin film, while oxygenated stoichiometric cubic $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3}$ thin films are observed to be strain free. The structural phase and stoichiometry are found to govern the nature and mechanism of magnetic interactions in these films. The emergence of unusual weak ferromagnetism in oxygen stoichiometric hexagonal SMO films established a root towards the local structural distortion as confirmed through the Raman spectroscopy and extended x-ray absorption fine structure measurements. This work proves for us the idea that the oxygen deficiency is not the necessary effect of strain; rather, it is the cause of strain for topotactic SMO film.