Effect of magnetic impurities on superconductivity and spin correlation of La2-xSrxCuO4

In order to investigate the effect of magnetic impurities systematically, the superconducting phase diagram is investigated by using a concentration-graded single crystal of La2-xSrxCu0.97Ni0.03O4 with x between 0.10 and 0.20. The anomalous suppression of Tc seen in the impurity-free system at around x=0.12, disappears upon 3% Ni-substitution and the bulk superconductivity is drastically depressed as well as Tc below x∼0.12. In contrast to non-magnetic Zn-substitution no static spin correlation is observable in the 2% Ni-substituted La1.85Sr0.15Cu0.98Ni0.02O4 (Tc=28 K). On the other hand, well-defined incommensurate magnetic peaks appear down to ω=0.4 meV. The correlation length evaluated from the inelastic peak-width is ∼50 Angst, which is comparable to that of 1.2% Zn-substituted La1.86Sr0.14Cu0.988Zn0.012O4 (∼70 Angst)