Muon spin relaxation and magnetic susceptibility studies of the effects of nonmagnetic impurities on the Cu spin dynamics and superconductivity in La _2-xSr_xCu_1-yZn_yO₄ around x=0.115

Zero-field muon-spin-relaxation (μSR) and magnetic-susceptibility measurements have been carried out in La_2-xSr_xCu _1-yZn_yO₄ with x=0.10, 0.115, and 0.13 changing the Zn concentration y finely up to 0.10, with the aim to clarify effects of the nonmagnetic impurity Zn on the Cu-spin dynamics and superconductivity. The μSR measurements have revealed that, in each x, a magnetic order of Cu spins is observed at y∼0.0075, while it disappears and Cu spins turn into a fast fluctuating state for y>0.03. From the magnetic-susceptibility measurements, on the other hand, it has been found that the volume fraction of the superconducting state rapidly decreases through the slight doping of Zn and that its y dependence corresponds to the y dependence of the volume fraction of the fast fluctuating region of Cu spins estimated from the μSR results. Both the rapid decrease of the volume fraction of the superconducting state and the formation of the magnetic order through the slight doping of Zn can be interpreted in terms of the development of the so-called "Swiss cheese" model. That is, it is concluded that Cu spins in a nonsuperconducting region around Zn exhibit slowingdown of the fluctuations or form an incoherent or coherent static magnetic order. Moreover, the formation of a nonsuperconducting region around Zn is considered to be due to the pinning of the dynamical spin correlation or dynamical stripe correlations.