  We report on a detailed neutron diffraction and $^1$H-NMR study on the
frustrated spin-1/2 chain material linarite, PbCuSO$_4$(OH)$_2$, where
competing ferromagnetic nearest neighbor and antiferromagnetic next-nearest
neighbor interactions lead to frustration. From the magnetic Bragg peak
intensity studied down to 60 mK, the magnetic moment per Cu atom is obtained
within the whole magnetic phase diagram for $H \parallel b$ axis. Further, we
establish the detailed configurations of the shift of the SDW propagation
vector in phase V with field and temperature. Finally, combining our neutron
diffraction results with those from a low-temperature/high-field NMR study we
find an even more complex phase diagram close to the quasi-saturation field
suggesting that bound two-magnon excitations are the lowest energy excitations
close to and in the quasi-saturation regime. Qualitatively and
semi-quantitatively, we relate such behavior to $XYZ$ exchange anisotropy and
contributions from the Dzyaloshinsky-Moriya interaction to affect the magnetic
properties of linarite.
