Impurity effect on the diagonal incommensurate spin correlations in La2-x Srx Cu O4

Neutron-scattering experiments were performed on Zn and Ni doped La1.95 Sr0.05 Cu O4 to study the impurity effect on the diagonal incommensurate spin correlations. Zn doping reduces the incommensurability and enhances the correlation length just slightly. On the other hand, Ni doping quickly destroys the incommensurability and restores Néel ordering, indicating a strong effect on hole localization. This suggests that Ni is doped as Ni3+ or that doped Ni2+ and a hole form a strongly bound state with the Zhang-Rice character. On the basis of the experimental results, the validity of the stripe and spiral models is discussed.