SUPERCONDUCTING AND MAGNETIC PHASE BOUNDARIES IN BI2SR2CA1-XMXCU2O8, WITH M = Y, GD, AND PR

The temperature dependences of the electrical resistivity, magnetic susceptibility, and specific heat have been measured in Bi2Sr2Ca1-xMxCu2O8, where M = Y, Gd, and Pr, for concentrations 0 less-than-or-equal-to x less-than-or-equal-to 1.0 and temperatures 1.6 K less-than-or-equal-to T less-than-or-equal-to 300 K. All three dopants substitute a ion for divalent Ca and cause a depression of T(c) observable in the resistivity and susceptibility. Both Pr and Gd retain their free-ion magnetic moment and appear to cause little, if any, magnetic pair breaking. Instead, the dominant suppression mechanism in all three cases is driven by the filling of the Cu 3d hole by the extra electron and the breaking of the Cu 3d-O 2p hybridization. Consequent localization of Cu 3d holes causes an observable antiferromagnetic ordering of Cu ions within the planes in the case of Y. The evidence for Cu ordering for Gd and Pr is obscured by the large Curie contribution to the magnetic susceptibility due to the rare-earth ions.