Nature of the magnetic stripes in fully oxygenated La 2 CuO 4 + y

We present triple-axis neutron scattering studies of static and dynamic magnetic stripes in an optimally oxygen-doped cuprate superconductor, ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4+y}$, which exhibits a clean superconducting transition at ${T}_{c}=42\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Polarization analysis reveals that the magnetic stripe structure is equally represented along both of the tetragonal crystal axes and that the fluctuating stripes display significant weight for in-plane as well as out-of-plane spin components. Both static magnetic order as well as low-energy fluctuations are fully developed in zero applied magnetic field and the low-energy spin fluctuations at $\ensuremath{\hbar}\ensuremath{\omega}=0.3\text{--}10\phantom{\rule{0.28em}{0ex}}\mathrm{meV}$ intensify on cooling. We interpret this as an indication that superconductivity and low-energy spin fluctuations coexist microscopically in spatial regions which are separated from domains with static magnetic order.