Oxygen content variation and cation doping dependence of (La){sub 1.4}(Sr{sub 1-y}Ca{sub y}){sub 1.6}Mn{sub 2}O{sub 7{+-}}{sub {delta}} (y=0,0.25,0.5) bilayered manganites
- Dipartimento di Chimica Fisica 'M. Rolla', INSTM, IENI/CNR Unita di Pavia of Universita di Pavia, V. le Taramelli 16, I-27100 Pavia (Italy)
- CNISM, Unita di Pavia and Dipartimento di Fisica 'A. Volta', Universita di Pavia, Via Bassi 6, I-27100 Pavia (Italy)
The results of the synthesis and characterization of the optimally doped (La){sub 1.4}(Sr{sub 1-y}Ca{sub y}){sub 1.6}Mn{sub 2}O{sub 7{+-}}{sub {delta}} solid solution with y=0, 0.25, and 0.5 are reported. By progressively replacing the Sr with the smaller Ca, while keeping fixed the hole concentration due to the divalent dopant, the 'size effect' of the cation itself on the structural, transport, and magnetic properties of the bilayered manganite has been analyzed. Two different annealing treatments of the solid solution, in pure oxygen and in pure argon, allowed us to also study the effect of the oxygen content variation. Structure and electronic properties of the samples have been investigated by means of x-ray powder diffraction and x-ray absorption spectroscopy measurements. Magnetoresistivity and static magnetization measurements have been carried out to complete the samples characterization. Oxygen annealing of the solid solution, which showed a limit for y{approx}0.5, induces an increase of the Mn average valence state and a transition of the crystal structure from tetragonal to orthorhombic while the argon annealing induces an oxygen understoichiometry and, in turn, a reduction of the Mn average valence state. Along with the Ca substitution, the Jahn-Teller distortion of the MnO{sub 6} octahedra is reduced. This has been directly connected to a general enhancement of the transport properties induced by the Ca doping. For the same cation composition, oxygen overstoichiometry leads to higher metal-insulator transition temperatures and lower resistivity values. Curie temperatures (T{sub C}) are reduced by increasing the Ca doping. The lower T{sub C} for all the annealed samples with respect to the as-prepared ones are connected to the strong influence on the magnetic interactions of the point defects due to the {delta}-variation.
- OSTI ID:
- 20853490
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 74, Issue 6; Other Information: DOI: 10.1103/PhysRevB.74.064104; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION SPECTROSCOPY
ANNEALING
ARGON
CALCIUM COMPOUNDS
CATIONS
CONCENTRATION RATIO
CURIE POINT
DOPED MATERIALS
HOLES
JAHN-TELLER EFFECT
LANTHANUM COMPOUNDS
MAGNETIC PROPERTIES
MAGNETIZATION
MAGNETORESISTANCE
MANGANATES
ORTHORHOMBIC LATTICES
OXYGEN
PHASE TRANSFORMATIONS
POINT DEFECTS
SOLID SOLUTIONS
STRONTIUM COMPOUNDS
VALENCE
VARIATIONS
X-RAY DIFFRACTION
X-RAY SPECTRA
X-RAY SPECTROSCOPY