Structural and magnetic study of LaBaCoCuO{sub 5+{delta}}

The structure and magnetic properties of the compound LaBaCuCoO{sub 5+{delta}} have been studied for the non-stoichiometric oxygen concentration {delta}{approx_equal}0.6. The structure is pseudo-cubic with a tripled perovskite unit cell. The crystal structure was determined by a combined Rietveld fit to neutron and synchrotron x-ray powder diffraction data in the orthorhombic Pmmm space group, with cell parameters a=3.9223(3) A, b=3.9360(3) A, c=11.7073(8) A, and V=180.74(2) A{sup 3} (room temperature). Antiferromagnetic ordering of Cu and Co magnetic moments is observed below 205(4) K. The magnetic structure with cell a{sub M}=2a, b{sub M}=2b, and c{sub M}=2c, could be described with the Shubnikov space group Fmmm{sup '}. The magnetic moments of both equivalent Cu/Co sites were determined at 50 and 170 K to be 0.83(3){mu}{sub B} and 0.58(3){mu}{sub B}, respectively, consistent with one unpaired electron per atom. The fit of the intensities to a simple mean field magnetic model appeared to be insufficient to account for the variation of moments at temperatures close to T{sub N} while a three dimensional Heisenberg model could improve the fit. Susceptibility measurements between 4 and 350 K also show irreversibility below 150 K. The local environments of Cu and Co were studied by extended x-ray absorption fine structure spectroscopy at both absorption edges. Cu atoms adopt an elongated octahedral or square-based pyramidal oxygen environment which suggests mainly the presence of Cu(II) in the structure. Co adopts different local environments, depending on the electronic and spin states.