  We present results of magnetic neutron diffraction experiments on the
co-doped super-oxygenated La(2-x)Sr(x)CuO(4+y) (LSCO+O) system with x=0.09. The
spin-density wave has been studied and we find long-range incommensurate
antiferromagnetic order below T_N coinciding with the superconducting ordering
temperature T_c=40 K. The incommensurability value is consistent with a
hole-doping of n_h~1/8, but in contrast to non-superoxygenated
La(2-x)Sr(x)CuO(4) with hole-doping close to n_h ~ 1/8 the magnetic order
parameter is not field-dependent. We attribute this to the magnetic order being
fully developed in LSCO+O as in the other striped lanthanum-cuprate systems.
