Static magnetism in superconducting stage-4 La2CuO4+y(y=0.12)

Zero-field (ZF) and transverse-field (TF) mu SR measurements have been performed on a superconducting La2CuO4+y crystal with y = 0.12 where excess oxygen is intercalated to form a stage-4 structure. Measurements are made on the same single-crystal sample studied in the neutron scattering measurements of Lee ct al. [Phys. Rev. B 60 (1999) 3643] who find that both superconductivity and static incommensurate magnetic modulation develop below T-c similar to T-N similar to 42 K. The amplitude of the muon precession signal observed in ZF-mu SR increases progressively below T-N and saturates at T --> 0 to the value which indicates that a static magnetic field from Cu moments exists in only a part of muon sites corresponding to a magnetic site fraction of V-M = 41%. The observed frequency similar to 3.5 MHz of the precession signal suggests the development of a large (at least 0.4 mu(B)) static Cu moment near the "magnetic" muon sites. Comparing the TF-mu SR results with computer simulations, we obtained V-M(T --> 0) = 42%. (C) 2000 Elsevier Science B.V. All rights reserved.