Muon-spin-relaxation and magnetic-susceptibility studies of the effects of the magnetic impurity Ni on the Cu-spin dynamics and superconductivity in La_2-xSr_xCu_1-yNi_yO₄ with x=0.13

Effects of the magnetic impurity Ni on the Cu-spin dynamics and superconductivity have been studied in La_2-xSr_xCu _1-yNi_yO₄ with x=0.13 changing y finely up to 0.10. Compared with the case of the non-magnetic impurity Zn, it has been found from the muon-spin-relaxation measurements that a large amount of Ni is required to stabilize a magnetic order of Cu spins. However, the evolution toward the stabilization of the magnetic order with increasing impurity concentration is qualitatively similar to each other. The area of the non-superconducting and slowly fluctuating or static region of Cu spins around Ni has been found to be smaller than that around Zn, suggesting that the pinning of rather long-ranged dynamical spin correlation such as the so-called dynamical stripe by Ni is weaker than that by Zn. This may be the reason why Zn destroys the superconductivity in the hole-doped high-T_c cuprates more markedly than Ni.