  Neutron diffraction and 7Li-NMR have been applied to determine the
multiferroic system LiCu2O2, which has four chains (ribbon chains) of
edge-sharing CuO4 square planes in a unit cell. We have confirmed that there
are successive magnetic transitions at TN1=24.5 K and TN2=22.8 K. In the T
region between TN1 and TN2, the quasi one-dimensional spins (S=1/2) of Cu2+
ions within a chain have a collinear and sinusoidally modulated structure with
Cu-moments parallel to the c-axis and with the modulation vector along the
b-axis. At T < TN2, an ellipsoidal helical spin structure with the
incommensurate modulation has been found. Here, we present detailed parameters,
describing the modulation amplitudes, helical axis vectors as well as the
relative phases of the modulations of four ribbon chains, which can well
reproduce both the NMR and neutron results in the two magnetically ordered
phases. This finding of the rather precise magnetic structures enables us to
discuss the relationship between the magnetic structure and the multiferroic
nature of the present system in zero magnetic field, as presented in our
companion paper (paper I), and open a way how to understand the reported
electric polarization under the finite magnetic field.
