Crystal and magnetic structure of NdBaCo2O5+δ: Spin states in a perovskite-derived, mixed-valent cobaltite

We report results of neutron powder diffraction studies on the crystallographic and magnetic structures of the compounds NdBaCo2O5+δ (δ=0.0, 0.5). Long-range antiferromagnetic order is found for the δ=0.0 compound, but no evidence of long-range charge-ordering is observed. The δ=0.5 compound shows poor long-range magnetic order, and the absence of such magnetic order is speculated to result from the particular ordered defect crystal structure of this material.