On magnetic ordering in heavily sodium substituted hole doped lanthanum manganites

Mixed valence manganite system with monovalent sodium substituted lanthanum manganites form the basis of the present work. Lanthanum manganites belonging to the series La_1-xNa_xMnO₃ with x=0.5-0.9 were synthesized using modified citrate gel method. Variation of lattice parameters and unit cell volume with Na concentration were analyzed and the magnetization measurements indicated ferromagnetic ordering in all samples at room temperature. Low temperature magnetization behavior indicated that all samples exhibit antiferromagnetism along with ferromagnetism and it has also been observed that antiferromagnetic ordering dominates ferromagnetic ordering as concentration is increased. Evidence for such a magnetic inhomogeneity in these samples has been confirmed from the variation in Mn³⁺/Mn⁴⁺ ion ratio from X-ray Photoelectron Spectroscopy and from the absorption peak studies using Ferromagnetic Resonance Spectroscopy.