  We discuss the magnetization process slightly below the saturation field in
frustrated magnets. A condensation of bound magnons on the spin-polarized state
induces either a spin nematic phase or a state with phase separation. The
(effective) interaction between the bound magnon pairs not only is crucial to
the stability of the nematic phase, but also determines the slope of the
magnetization curve near saturation. We generally derive the expression of this
interaction by using the perturbative scattering theory. By applying the method
to coupled zigzag chains LiCuVO4, we find the positive pair-pair interaction
implying the stability of the spin nematic phase. We also point out that the
magnetization curve of LiCuVO4 is almost vertical (i.e. very large dM/dH) near
the saturation exhibiting one-dimensional feature despite non-negligible
interchain couplings.
