Magnetic Superstructures of Cupric Oxide CuO as Ordered Arrangements of One-Dimensional Antiferromagnetic Chains

In cupric oxide CuO, each Cu(2+) ion has 12 nearest-neighbor Cu(2+) ions grouped into six pairs related by inversion symmetry. The relative strengths of the Cu-O-Cu superexchange interactions in cupric oxide CuO were estimated by spin dimer analysis to confirm that the strongest superexchange interactions form one-dimensional antiferromagnetic chains along the [101] direction, and the remaining interactions are weak. We analyzed ordered arrangements of these one-dimensional antiferromagnetic chains to examine why the antiferromagnetic phase transition of CuO below 212.5 K adopts a (2a, b, 2c) superstructure. The local spin arrangement around each Cu(2+) ion is more balanced in the ordered spin structures leading to a (2a, b, 2c) supercell than in any other ordered spin structures.