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

Zero-field (ZF) and transverse-field (TF) μSR 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 et al. [Phys. Rev. B 60 (1999) 3643] who find that both superconductivity and static incommensurate magnetic modulation develop below Tc∼TN∼42K. The amplitude of the muon precession signal observed in ZF-μSR increases progressively below TN 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 VM=41%. The observed frequency ∼3.5 MHz of the precession signal suggests the development of a large (at least 0.4μB) static Cu moment near the “magnetic” muon sites. Comparing the TF-μSR results with computer simulations, we obtained VM(T→0)=42%.