Single-crystal growth and dependences on the hole concentration and magnetic field of the magnetic ground state in the edge-sharing CuO${}_2$ chain system Ca${}_{2+x}$Y${}_{2-x}$Cu${}_5$O${}_{10}$

Abstract

We have succeeded in growing large-size single-crystals of Ca${}_{2+x}$Y${}_{2-x}$Cu${}_5$O${}_{10}$ with $0\le x\le 1.67$ and measured the magnetic susceptibility, specific heat and magnetization curve, in order to study the magnetic ground state in the edge-sharing CuO${}_2$ chain as a function of hole concentration and magnetic field. In $0\le x\le 1.3$, 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 $\sim$ 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 Ca${}_{1-x}$CuO${}_2$ has been found in Ca${}_{2+x}$Y${}_{2-x}$Cu${}_5$O${}_{10}$.

13 pages, 12 figures, 1 table