Single-crystal growth and dependences on the hole concentration and magnetic field of the magnetic ground state in the edge-sharing CuO₂ chain system Ca₂₊ₓY₂₋ₓCu₅O₁₀

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We have succeeded in growing large-size single-crystals of Ca₂₊ₓY₂₋ₓCu₅O₁₀ with 0 ≤ x ≤ 1.67 and measured the magnetic susceptibility, specific heat and magnetization curve, in order to study the magnetic ground state in the edge-sharing CuO₂ chain as a function of hole concentration and magnetic field. In 0 ≤ x ≤ 1.3, it has been found that an antiferromagnetically ordered phase with the magnetic easy axis along the b-axis is stabilized and that a spin-flop transition occurs by the application of magnetic fields parallel to the b-axis. The antiferromagnetic transition temperature decreases with increasing x and disappears around x = 1.4. Alternatively, a spin-glass phase appears around x = 1.5. At x = 1.67 where the hole concentration is 1/3 per Cu, it appears that a spin-gap state is formed owing to the formation of spin-singlet pairs. No sign of the coexistence of an antiferromagnetically ordered state and a spin-gap one suggested in Ca₁₋ₓCuO₂ has been found in Ca₂₊ₓY₂₋ₓCu₅O₁₀.