Effect of oxygen stoichiometry on properties of La0.815Sr0.185MnO3+d

The effect of oxygen stoichiometry on properties of La0.815Sr0.185MnO3+d wa s studied for samples with oxygen content controlled by quenching from high temperatures (700-1400 degrees C) in air, cooling under low oxygen partial pressure, and annealing at high oxygen pressure. The oxygen content determ ined from thermogravimetric analysis was found to vary within a range of 3. 00-3.10. At room temperature the lattice parameters of the rhombohedral str ucture (R (3) over bar c) decrease linearly with increasing oxygen content. The rhombohedral-orthorhombic structural transition temperature decreases abruptly with increasing oxygen content while the Curie temperature increas es with increasing oxygen content, reaching a maximum at d similar to 0.04, and then decreases. The saturation magnetization decreases linearly with i ncreasing oxygen content indicating increasing Mn4+ concentration, i.e., ho le doping by cation vacancies. Finally the magnetoresistance effect decreas es with increasing d. (C) 2000 American Institute of Physics. [S0021-8979(0 0)26408-6].