STUDY OF THE MAGNETIC PHASE-DIAGRAM OF Y1-XCAXBA2CU3O6

We have studied the magnetic phase diagram for the bilayer compound Y1 -xCaxBa2Cu3O6 in the regime of low doping (hole concentration within a CuO2 plane, p(sh) < 0.1). For p(sh) < 0.03, the data demonstrate the freezing of the spin degrees of freedom associated with the doped hole s into a spin-glass-like state which is superimposed on the preexistin g long range order of the Cu2+ spins. Only a single spin-glass like tr ansition at a temperature T-g is observed for samples in the hole conc entration range 0.03 < p(sh) < 0.1. While the threshold for the occurr ence of superconductivity is almost the same (p(sh) > 0.06) for the Y1 -xCaxBa2Cu3O6 and the La2-xSrxCuO4 systems, the magnetic correlations that coexist with superconductivity are considerably stronger in the b ilayer Y1-xCaxBa2Cu3O6 system as indicated by significantly increased transition temperatures T-g.