Y-89 NMR-STUDY OF ZN-INDUCED LOCAL MOMENTS AND PAIR-BREAKING IN Y(BA1-YLAY)(2)(CU1-XZNX)(4)O-8

(89)y NMR measurements have been carried out and modeled for underdope d Y(Ba1-yLay)(2)(Cu1-xZnx)(4)O-8 superconductors. We find that the dat a are well described by Zn inducing a local moment, leading to a spin- density oscillation and an additional Y-89 hyperfine field. We find an exchange energy increasing from similar to 50 to similar to 104 meV a s the hole concentration is increased and an induced local moment whic h declines from 1.35 to 1.06 mu B. Magnetic pair breaking can fully ac count for the decrease in T-c with Zn substitution for the La-free mat erials. With progressive underdoping, magnetic pair breaking is increa singly unable to account for the decline in T-c with Zn substitution s uggesting that Zn weakens the pairing interaction as in the spin-fluct uation pairing model.