Ni-impurity effects on incommensurate spin correlations in the superconducting phase of La2-xSrxCuO4 near the spin-glass phase boundary

Neutron scattering experiments were carried out to explore Ni-impurity effects on static spin correlations in La2-xSrxCuO4 in the vicinity of the superconductor-insulator boundary where both parallel and diagonal spin-density modulations (SDMs) coexist at low temperature. Dilute Ni substitution completely destroys the bulk superconductivity and alters well-defined incommensurate peaks of Ni-free SDMs into a single broad peak at (pi, pi). As the Ni concentration (y) reaches similar to x, the magnetic diffuse scattering is transformed to an intense sharp Bragg peak, corresponding to a three-dimensional antiferromagnetic (AF) order in bulk. T-N of such Ni-induced AF order depends on x and appears to disappear at x similar to 0. 1. A simplified cross section for the Q spectra taking into account the orthorhombic domain structure reproduces the Ni-impurity effect on the static spin correlations well, which results in a decreasing incommensurability of both types of SDMs. These effects are approximately ascribed by a reduction in the number of mobile holes, or by the effective hole number x(eff) = x - y, similarly to the case of diagonal SDMs in insulating spin-glasses.