Neutron-scattering study of static antiferromagnetic correlations in ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{Cu}}_{1-y}{\mathrm{Zn}}_y{\mathrm{O}}_4$

Neutron-scattering measurements have been performed to search for possible elastic incommensurate magnetic peaks in superconducting ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ with $x=0.10,$ 0.12, and 0.15. The most dramatic effects are found for $x=0.12;$ in this case, the peak intensity first appears at the onset of superconductivity $T_c(=31\mathrm{}\hspace{0.5em}\mathrm{K}).\mathrm{}$ The resolution-limited peak width indicates that the static magnetic correlation length exceeds 200 Å isotropically in the ${\mathrm{CuO}}_2$ planes. Weak elastic peaks are also observed at low temperatures for $x=0.10\mathrm{}$ while for $x=0.15\mathrm{}$ any incommensurate elastic scattering is below the limit of detectability. Elastic peaks are observed in Zn-substituted nonsuperconducting ${\mathrm{La}}_{1.88}{\mathrm{Sr}}_{0.12}{\mathrm{Cu}}_{0.97}{\mathrm{Zn}}_{0.03}{0}_4.$ However, in this case, the Zn substitution degrades the magnetic order; the peak appears at lower temperature (17 K) and the correlation length is shorter (80 Å) than that in the Zn-free $x=0.12\mathrm{}$ sample.