Excess Oxygen in Low Sr Doping La1-xSrxMnO3+DELTA Epitaxial Films

Thin films of La1-xSrxMnO3+ (x=0.05, 0.10, 0.14) on LaAlO3 substrate have been prepared by employing spin coating methods. The as-prepared films crystallized at 1223 K in 1 atm oxygen show a complete in-plane epitaxy and exhibit singlecrystal-like transport properties without intergrain spin-polarized scattering. In order to reduce excess oxygen, the asprepared films were further heat-treated in 1–20 Pa oxygen at 873 to 1073 K. The excess oxygen content in the films was evaluated by assuming linear dependence of entropy and enthalpy of defect formation against Sr content x in the Roosmalenʹs defect model. The measured lattice parameters on these oxygen-reduced films show good agreement with the values from the above defect model. Both the calculated and the experimental results show that Mn4+ proportion for the as-prepared films is almost independent of Sr doping level x, and in order to get films without excess oxygen, the films must be treated in 1 Pa oxygen at 1073 K. The magnetic and transport properties measured on these films show higher Tc than the published electric phase diagram from the single crystal samples. We assumed that the La site vacancy intrinsically incorporated in the singlecrystal samples during the growth process might be the cause of this difference.