Synthesis and magnetic properties of the quasi-one-dimensional compound Ca_0.83(Cu_1-xCo_x)O₂

A new solid solution of the quasi-one-dimensional composite crystal, Ca_0.83(Cu_1-xCo_x)O₂(0≤x≤0.30), has been synthesized under 1 atm of O₂ at 830°C. The non-doped compound Ca_0.83CuO₂ consists of two interpenetrating monoclinic subsystems of the [Ca] atoms and the edge-shared square planar [CuO₂] chains. Upon increasing x, both the subsystems undergo a phase change from monoclinic to orthorhombic (M-O). The M-O change occurs at x∼0.04 for the [(Cu,Co)O₂] subsystem, while such a change occurs at x∼0.17 for the [Ca] subsystem. Magnetic susceptibility measurements show an evolution from a short-range ordered state near x=0 to a long-range antiferromagnetic state (T_N=10-15 K) for the samples with x≥0.15. The effective magnetic moment μ_eff is found to increase with increasing x from 2.1 μ_B for x=0.10 to 3.0 μ_B for x=0.30, suggesting that the solid solution can be regarded as Ca _0.83[Cu_0.66²⁺Cu_0.34-x ³⁺Co_x³⁺]O₂, in which a mixed state of Cu²⁺(S=1/2), Cu³⁺(S=0) and high-spin Co ³⁺(S=2) ions is realized.