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The results of the synthesis and characterization of the optimally doped(La)1.4(Sr1-yCay)1.6Mn2O7 solid solution with y=0, 0.25 and 0.5 are reported.By progressively replacing the Sr with the smaller Ca, while keeping fixed thehole-concentration due to the divalent dopant, the 'size effect' of the cationitself on the structural, transport and magnetic properties of the bilayeredmanganite has been analysed. Two different annealing treatments of the solidsolution, in pure oxygen and in pure argon, allowed also to study the effect ofthe oxygen content variation. Structure and electronic properties of thesamples have been investigated by means of X-ray powder diffraction and X-rayabsorption spectroscopy measurements. Magnetoresistivity and staticmagnetization measurements have been carried out to complete the samplescharacterization. Oxygen annealing of the solid solution, that showed a limitfor about y=0.5, induces an increase of the Mn average valence state and atransition of the crystal structure from tetragonal to orthorhombic while theargon annealing induces an oxygen under-stoichiometry and, in turn, a reductionof the Mn average valence state. Along with the Ca substitution, theJahn-Teller distortion of the MnO6 octahedra is reduced. This has been directlyconnected to a general enhancement of the transport properties induced by theCa-doping. For the same cation composition, oxygen over-stoichiometry leads tohigher metal-insulator transition temperatures and lower resistivity values.Curie temperatures (TC) reduce by increasing the Ca-doping. The lower TC forall the annealed samples with respect to the 'as prepared' ones are connectedto the strong influence on the magnetic interaction of the point defects due tothe oxygen content variation.Comment: 49 pages, 13 figure

physical review. b, condensed matter and materials physics

Oxygen content variation and cation doping dependence of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:mi>La</mml:mi><mml:msub><mml:mo>)</mml:mo><mml:mn>1.4</mml:mn></mml:msub><mml:mo>(</mml:mo><mml:msub><mml:mi>Sr</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>y</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Ca</mml:mi><mml:mi>y</mml:mi></mml:msub><mml:msub><mml:mo>)</mml:mo><mml:mn>1.6</mml:mn></mml:msub><mml:msub><…

Oxygen content variation and cation doping dependence of(La)1.4(Sr1−yCay)1.6<…