Modulated Crystal Structure and Spin/Hole Arrangement in the Chain Compound Ca_xCuO₂ (x=0.8240)

抄録

The crystal structure of Ca_xCuO₂ (x=0.8240) has been studied by the Rietveld refinement of X-ray diffraction data using a modulated-structure analysis technique. Hole distribution was determined by bond-valence sum calculation using the obtained Cu-O inter-atomic distances. The results revealed that every third Cu site along a chain tends to be occupied by a hole. Furthermore, it was found that the Cu-O-Cu bond-angles for hole-unoccupied Cu sites are smaller than 90°. This suggests that the nearest-neighbor magnetic interaction J₁ is ferromagnetic and its magnitude is comparable to the next nearest-neighbor antiferromagnetic interaction J₂. Based on the obtained hole distribution and the signs of the magnetic interactions between spins, we proposed a possible spin/hole arrangement model in the chain, which includes a main sequence of …↑\bigcirc↓↓\bigcirc↑… in most parts of the chain.