Effect of vacuum annealing on oxygen stoichiometry and resistivity of sol-gel derived La0.7Sr0.3MnO3-delta films

We have studied the dependence of the resistivity and magnetoresistance (MR) of epitaxial (0 0 1) La0.7Sr0.3MnO3-delta/(0 0 1) LaAlO3 firms on controlled vacuum annealing. First, La0.7Sr0.3MnO3-delta films grown by sol-gel process were annealed at O-2 (1 atm. oxygen)/1170 K/1 h (we call this as-prepared films); subsequently, these as-prepared films were annealed in vacuum (similar to 10(-6) torr/2 h) at different temperatures, i.e. 720 K, 770 K, 820 K, 920 K, to systematically reduce the oxygen stoichiometry. The resistivity increases systematically with increasing annealing temperature in accord with oxygen content variation. The resistivity shows a metallic behavior (as-prepared films), metal-insulator transitions (films annealed at 720 K, 770 K) and an insulating behavior (firms annealed at 820 K, 920 K). Significant MR is observed predominantly near the resistivity peak for the metallic films and at low temperature for the insulating films. These observations demonstrate that the oxygen content, the resistivity and MR behavior of manganese oxides are precisely controllable via vacuum annealing. (C) 1997 Published by Elsevier Science Ltd.