Cation radii and oxygen deficiency effects on the structural, magnetic, and electrical properties in La_(1-x)Sr_xMnO_(3-δ)□_δ manganites (x = 0.2-0.5 and δ = 0.1)

摘要

The series of non-stochiometric strontium substituted lanthanium manganites La_(1-x)Sr_xMnO_(3-δ)□_δ (δ=0.1, x=0.2-0.5) has been studied and show the effect of oxygen deficiency on the structural transition, magnetic and electrical properties of these compounds. Polycrystalline samples La_(1-x)Sr_xMnO_(3-δ)□_δ were synthesised by a new method at atmospheric pressure. In this series of manganites, the Mn~(4+) content is systematically decreased due to increase in the non-stoichiometry. X-ray diffraction analysis shows a phase transition from orthorhombic to rhombohedral systems for 0.2 ≤ x ≤ 0.5. The material is ferromagnetic for 0.3 ≤ x ≤0.5 and antiferromagnetic for x =0.2. The Curie temperature T_C increases with increasing x. The resistivity as a function of temperature shows that samples with x=0.3 and ferromagnetic metal between T_(CF) and T_P becomes ferromagnetic insulators below T_(CF) where charge-ordering seems to appear.