Effects of the oxygen nonstoichiometry on the physical properties of La0.7Sr0.3MnO3-delta square delta manganites (0 <=delta <= 0.15)

We present the oxygen deficiency effects on the structural, magnetic, and e lectrical properties in La(0.7)Sr(0.3)MnO(3-delta)square(delta) solution wh ere square is a vacancy and 0 less than or equal to delta less than or equa l 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+ con tent is systematically increased due to the increase in the nonstoichiometr y delta. X-ray diffraction analysis shows a phase transition from a rhomboh edral 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 o r 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 me asurements as a function of temperature show a remarkable behavior for the La0.7Sr0.3MnO2.9 compound; it is ferromagnetic metallic for 115 less than o r equal to T less than or equal to 180 K and becomes ferromagnetic insulato r below 115 K, where a charge ordering seems to appear. The difference in t he hopping energies in our samples can be related to the existence of two c rystallographic structures, one orthorhombic and the other rhombohedral. (C ) 2000 Academic Press.