Effects of the oxygen nonstoichiometry on the physical properties of La0.7Sr0.3MnO3-δ□δ manganites (0≤δ≤0.15)

We present the oxygen deficiency effects on the structural, magnetic, and electrical properties in La(0.7)Sr(0.3)MnO(3-delta)square(delta) solution where square is a vacancy and 0 less than or equal to delta less than or equal to 0.15. Polycrystalline samples La(0.7)Sr(0.3)MnO(3-delta)square(delta) were synthesized by a new method. In this series of manganites the Mn3+ content is systematically increased due to the increase in the nonstoichiometry delta. X-ray diffraction analysis shows a phase transition from a rhombohedral to an orthorhombic system at 0.075 less than or equal to 6 less than or equal to 0.1. The material is ferromagnetic for 0 less than or equal to delta less than or equal to 0.1 and antiferromagnetic for 0.125 less than or equal to delta less than or equal to 0.15. The Curie temperature T-C and saturation magnetization M-s decrease with increasing delta. Resistivity measurements as a function of temperature show a remarkable behavior for the La0.7Sr0.3MnO2.9 compound; it is ferromagnetic metallic for 115 less than or equal to T less than or equal to 180 K and becomes ferromagnetic insulator below 115 K, where a charge ordering seems to appear. The difference in the hopping energies in our samples can be related to the existence of two crystallographic structures, one orthorhombic and the other rhombohedral. (C) 2000 Academic Press.