Cation Radii and Oxygen Deficiency Effects on the Structural, Magnetic, and Electrical Properties in La1−xSrxMnO3−□ Manganites (x = 0.2-0.5 and  = 0.1)

The series of non-stochiometric strontium substituted lanthanium manganites La_1−xSr_xMnO_3−□_ ( = 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−xSr_xMnO_3−□_ were synthesised by a new method at atmospheric pressure. In this series of manganites, the Mn⁴⁺ 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.