Al NMR probe of local moments induced by an Al impurity in high-T-c cuprate La1.85Sr0.15CuO4

Al-27 and Cu-63 NMR measurements in 3% Al-doped La1.85Sr0.15CuO4 (LSCO) have revealed that the T dependences of the Knight shift, K-27(T), and the nuclear-spin-lattice relaxation rate, (27)(1/T-1), are dominated by local moments induced at neighboring Cu sites by the Al impurity. These experiments prove that spin fluctuation of induced moments is mainly due to the local spin-exchange coupling, J(sd), with conducting holes. This novel T dependence of (27)(1/T-1) has led to a reliable estimation of J(sd) = 0.055 eV, and the extraction of the T-c reduction rate, Delta T-c = 0.62 K/Al% based on the magnetic pair-breaking scheme, which is by more than I order of magnitude smaller than the experimental value of Delta T-c = 23 K/Al%.