Search

The optimally doped [La.sub.1.4][Sr.sub.0.8][Ca.sub.0.8]Mn2O7 bilayered manganite was investigated by high resolution neutron diffraction and magnetometry. The results show the absence of long-range magnetic order in this optimally doped manganite when the A-site of the structure is doped with equal proportions of isovalent Ca and Sr which might be due to a size effect coupled to the cation size mismatch between Sr and Ca ions.

The structural, electrical and magnetic characterization of the La(sub 1-x)Na(sub x)Mn(sub 1-y)Ru(sub x)O(sub 3+delta) (LNMRO) system with x = 0.05 and 0.15 and y = 0.005, and 0.15, is reported along with an investigation of the role of the oxygen content on the related redox properties. The analysis shows that ruthenium addition improves electrical and magnetic properties of nonoptimally cation-doped manganites, causing an increase of the Tc value and the insurgence of mangetoresistance effect.

The local structure and electronic properties of Mn in Na doped lanthanum manganites is investigated by means of Mn-K edge XAFS, at various temperatures ranging from RT to 30 K. It was found that the Mn (IV) content of the samples as determined by the chemical shift of the Mn-K edge is slightly different with respect to that calculated on the basis of the quasi-chemical equilibria leading to doping on the La site and to oxygen nonstoicchiometry.

The determination of oxygen diffusion coefficients for optimally doped manganite thin films of La0.85Na0.15MnO3 (LNMO) deposited by means of RF-magnetron sputtering onto SrTiO3 (100) and (110) is reported. The study of the oxygen diffusion is carried out by means of isothermal electric resistivity measurements. The values found for the oxygen diffusion coefficients are around 10(super -14)cm(super 2)s(super -1).

La(sub 1-x)NaMnO(sub 3+delta) samples with well-defined cation molecularity and oxygen contents (x = 0.05, x = 0.13, and -0.04