Evidence for Successive Doping-Induced Dimensionality Transitions in the Spin-Chain Compound Ca2+xY2-xCu5O10

We report the results of heat capacity, SQUID magnetometry, and x-ray diffraction studies of polycrystalline and magnetically aligned Ca 2+xY 2-xCu 5O (10), a quasi-1D compound. As holes are doped into the chains from x = 0-2, the data indicate a change from 3D long-range order to 1D chain behavior to cluster behavior. We quantitatively model the magnetic and thermal properties of heavily doped Ca 4Cu 5O (10) in terms of spin clusters. Anisotropic susceptibility data indicate a doping-independent easy axis of magnetization perpendicular to the planes containing the chains; also, a spin-flop transition is observed, providing a measure of the anisotropy field.