Effect of annealing on Curie temperature and phase transition in La0.55Sr0.08Mn0.37O3 epitaxial films grown on SrTiO3 (100) substrates by reactive radio frequency magnetron sputtering

• Mn-poor LSMO changed from monoclinic/orthorhombic to rhombohedral by oxygen supply.
• Mn-poor LSMO was increased TC by changed crystal symmetry, and it showed TC above RT.
• Annealed in air effectively supplied O2 more than O2 gas during sputtering
• EBSD is useful to evaluate crystal symmetry of complex oxide film from the substrate.

Mn-poor LaSrMnO3 (LSMO) epitaxial films were grown on SrTiO3 (100) substrates by radio frequency magnetron sputtering in an argon and oxygen gas mix, and then the samples were annealed in air at various temperatures (Ta). 2 theta-chi X-ray diffraction mapping, nano-beam diffraction analysis through transmission electron microscopy, and electron back scatter diffraction through scanning electron microscopy revealed that the crystal symmetry of the LSMO films changed from monoclinic/orthorhombic to rhombohedral on annealing in air. Curie temperature (TC) of the LSMO films was found to increase with increasing Ta, and become higher than the room temperature at Ta ≥ 861 °C, indicating that the cause of these changes was the filling of oxygen and the transition of the crystal symmetry into rhombohedral.