Charge Segregation, Cluster Spin-Glass and Superconductivity in La1.94Sr0.06CuO4

A {sup 63}Cu and {sup 139}La NMR/NQR study of superconducting (T{sub c}=8 K) La{sub 1.94} Sr{sub 0.06} CuO{sub 4} single crystal is reported. Coexistence of spin-glass and superconducting phases is found below {approximately}5 K from {sup 139}La NMR relaxation. {sup 63}Cu and {sup 139}La NMR spectra show that, upon cooling, CuO{sub 2} planes progressively separate into two magnetic phases, one of them having enhanced antiferromagnetic correlations. These results establish the antiferromagnetic-cluster nature of the spin glass. We discuss how this phase can be related to the microsegregation of mobile holes and to the possible pinning of charge stripes. {copyright} {ital 1999} {ital The American Physical Society }