Structural and magnetic study of LaBaCoCuO5+d

The structure and magnetic properties of the compound LaBaCuCoO5+d have been studied for the nonstoichiometric oxygen concentration d < 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= 3.9223s3d A, b = 3.9360s3d A,c = 11.7073s8d A, andV= 180.74s2d A 3 sroom temperatured. Antiferromagnetic ordering of Cu and Co magnetic moments is observed below 205s4d K. The magnetic structure with cell aM =2 a, bM =2 b, and cM =2 c, could be described with the Shubnikov space group Fmmm8. The magnetic moments of both equivalent Cu/ Co sites were determined at 50 and 170 K to be 0.83s3dmB and 0.58s3dmB, 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 TN 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 CusIId in the structure. Co adopts different local environments, depending on the electronic and spin states.